IL21

UniProt ID: Q9HBE4
Organism: Homo sapiens
Review Status: COMPLETE
๐Ÿ“ Provide Detailed Feedback

Gene Description

Interleukin-21 (IL21) is a secreted cytokine with immunoregulatory activity that belongs to the IL-15/IL-21 family. IL21 promotes the transition between innate and adaptive immunity and is critical for T follicular helper (Tfh) cell generation and maintenance, germinal center formation, and B cell differentiation. It induces immunoglobulin production (IgG1, IgG3) in B cells, regulates proliferation and maturation of natural killer (NK) cells in synergy with IL15, and stimulates interferon-gamma production in T cells and NK cells. IL21 signals through a receptor complex containing IL21R and the common gamma chain (IL2RG), activating the JAK-STAT pathway (primarily JAK1/JAK3 and STAT1/STAT3/STAT5). Expressed primarily by activated CD4+ T cells. Mutations cause common variable immunodeficiency 11 (CVID11).

Existing Annotations Review

GO Term Evidence Action Reason
GO:0001819 positive regulation of cytokine production
IBA
GO_REF:0000033 		ACCEPT
Summary: Phylogenetically inferred annotation supported by IL21's demonstrated role in cytokine regulation. IL21 stimulates IFN-gamma production in synergy with IL15 and IL18, and enhances IL-17 production. Consistent with experimental evidence.
GO:0045954 positive regulation of natural killer cell mediated cytotoxicity
IBA
GO_REF:0000033 		ACCEPT
Summary: Phylogenetically inferred annotation consistent with IL21's role in NK cell function. Supported by experimental data (PMID:18005035) showing IL21 activates NK cells and modulates their cytotoxic activity.
GO:0001819 positive regulation of cytokine production
IEA
GO_REF:0000117 		ACCEPT
Summary: ARBA-predicted annotation consistent with IL21's function. Duplicates IBA annotation with same term - maintain consistent action.
GO:0005125 cytokine activity
IEA
GO_REF:0000043 		ACCEPT
Summary: Core molecular function. IL21 is a secreted cytokine that binds to its receptor complex (IL21R/IL2RG) and activates downstream signaling. This is the primary molecular function of IL21.
GO:0005126 cytokine receptor binding
IEA
GO_REF:0000120 		KEEP AS NON CORE
Summary: Correct annotation. IL21 binds the IL21 receptor complex. This is essentially equivalent to cytokine activity for this protein. Keep but not core since cytokine activity is the primary MF term.
GO:0005576 extracellular region
IEA
GO_REF:0000120 		KEEP AS NON CORE
Summary: Correct general location term. IL21 is secreted. More specific term (extracellular space) is also annotated. Keep as supporting annotation.
GO:0005615 extracellular space
IEA
GO_REF:0000043 		ACCEPT
Summary: Duplicates NAS annotation from PMID:11081504. More specific than extracellular region. Maintain consistent action with curated annotation.
GO:0006952 defense response
IEA
GO_REF:0000117 		MARK AS OVER ANNOTATED
Summary: Very general term. IL21 does participate in immune defense but more specific terms (defense response to virus) are available. Term is too general for core function.
GO:0006955 immune response
IEA
GO_REF:0000002 		MARK AS OVER ANNOTATED
Summary: Very general term. All cytokine activity involves immune response. More specific terms are appropriate for IL21 function.
GO:0009615 response to virus
IEA
GO_REF:0000117 		KEEP AS NON CORE
Summary: General term. IL21 plays a role in antiviral immunity but more specific term (defense response to virus, GO:0051607) is more appropriate.
GO:0045954 positive regulation of natural killer cell mediated cytotoxicity
IEA
GO_REF:0000117 		ACCEPT
Summary: Duplicates IBA/IDA annotation for same term. ARBA-predicted. Consistent with experimental evidence. Maintain consistent action.
GO:0048468 cell development
IEA
GO_REF:0000117 		MARK AS OVER ANNOTATED
Summary: Very general term. IL21 is involved in specific cell development processes (NK cell, B cell, Tfh cell development) but this term is too broad. More specific terms should be used.
GO:0051251 positive regulation of lymphocyte activation
IEA
GO_REF:0000117 		KEEP AS NON CORE
Summary: Consistent with IL21 function. IL21 promotes B cell and T cell activation. Relatively general but accurate for IL21's immunoregulatory role.
GO:0005515 protein binding
IPI
PMID:32296183
A reference map of the human binary protein interactome. 		REMOVE
Summary: NON-INFORMATIVE: protein binding is too generic. Does not describe what IL21 binds or the functional consequence. For a cytokine, cytokine receptor binding (GO:0005126) or interleukin-2 receptor binding (GO:0005134) are more informative.
Supporting Evidence:
PMID:32296183
Apr 8. A reference map of the human binary protein interactome.
GO:0005886 plasma membrane
IPI
PMID:37339051
A structural blueprint for interleukin-21 signal modulation. 		MARK AS OVER ANNOTATED
Summary: This annotation likely refers to IL21 associating with plasma membrane via receptor binding (IL21R is membrane-bound). However, IL21 itself is a secreted protein, not a membrane protein. This may be misleading - IL21 is transiently at the membrane when bound to receptor but its primary location is extracellular.
Supporting Evidence:
PMID:37339051
2023 Jun 19. A structural blueprint for interleukin-21 signal modulation.
GO:0002314 germinal center B cell differentiation
IEA
GO_REF:0000107 		ACCEPT
Summary: Core function. IL21 is critical for germinal center formation and B cell differentiation. Supported by ISS annotation and mouse knockout data.
GO:0002639 positive regulation of immunoglobulin production
IEA
GO_REF:0000107 		ACCEPT
Summary: Core function. IL21 induces IgG1 and IgG3 production in B cells. This is one of the primary biological roles of IL21.
GO:0061470 T follicular helper cell differentiation
IEA
GO_REF:0000107 		ACCEPT
Summary: Core function. IL21 is implicated in the generation and maintenance of Tfh cells. Together with IL6, critical for effective antibody response to viral infection.
GO:0098586 cellular response to virus
IEA
GO_REF:0000107 		KEEP AS NON CORE
Summary: IL21 plays a role in antiviral immunity through multiple mechanisms. Consistent with defense response to virus annotation. Keep as supporting.
GO:0007259 cell surface receptor signaling pathway via JAK-STAT
NAS
PMID:17938255
The opposite effects of IL-15 and IL-21 on CLL B cells corre... 		KEEP AS NON CORE
Summary: IL21 signals through JAK1/JAK3 and STAT1/STAT3/STAT5. However, this term describes the pathway that IL21 TRIGGERS, not a process IL21 directly participates in. IL21 is the ligand that initiates this signaling. The annotation is reasonable but imprecise - IL21's role is to bind receptor and activate the pathway.
Supporting Evidence:
PMID:17938255
Oct 15. The opposite effects of IL-15 and IL-21 on CLL B cells correlate with differential activation of the JAK/STAT and ERK1/2 pathways.
GO:0016064 immunoglobulin mediated immune response
NAS
PMID:37339051
A structural blueprint for interleukin-21 signal modulation. 		MARK AS OVER ANNOTATED
Summary: IL21 promotes immunoglobulin production by B cells, thus indirectly supporting immunoglobulin-mediated immunity. However, IL21 itself does not directly participate in immunoglobulin-mediated immune responses - it's an upstream regulator.
Supporting Evidence:
PMID:37339051
2023 Jun 19. A structural blueprint for interleukin-21 signal modulation.
GO:0030101 natural killer cell activation
NAS
PMID:37339051
A structural blueprint for interleukin-21 signal modulation. 		ACCEPT
Summary: Supported by experimental evidence. IL21 activates NK cells and modulates their surface receptor expression. Core function in NK cell biology.
Supporting Evidence:
PMID:37339051
2023 Jun 19. A structural blueprint for interleukin-21 signal modulation.
GO:0002314 germinal center B cell differentiation
ISS
GO_REF:0000024 		ACCEPT
Summary: Duplicates IEA annotation. Based on manual transfer from mouse ortholog. Core function supported by multiple evidence types. Maintain consistent action.
GO:0002639 positive regulation of immunoglobulin production
ISS
GO_REF:0000024 		ACCEPT
Summary: Duplicates IEA annotation. Based on manual transfer from mouse ortholog. Core function supported by multiple evidence types. Maintain consistent action.
GO:0061470 T follicular helper cell differentiation
ISS
GO_REF:0000024 		ACCEPT
Summary: Duplicates IEA annotation. Based on manual transfer from mouse ortholog. Core function supported by multiple evidence types. Maintain consistent action.
GO:0098586 cellular response to virus
ISS
GO_REF:0000024 		KEEP AS NON CORE
Summary: Duplicates IEA annotation. Based on manual transfer from mouse ortholog. Consistent with IL21 antiviral role.
GO:0051607 defense response to virus
TAS
PMID:28798470
Identification of the novel 3' UTR sequences of human IL-21 ... 		ACCEPT
Summary: IL21 contributes to antiviral immunity through multiple mechanisms including enhancing NK cell cytotoxicity and T cell responses. Supported by literature.
Supporting Evidence:
PMID:28798470
Identification of the novel 3' UTR sequences of human IL-21 mRNA as potential targets of miRNAs.
GO:0042531 positive regulation of tyrosine phosphorylation of STAT protein
IDA
PMID:17673207
Cloning and characterization of an isoform of interleukin-21... 		ACCEPT
Summary: Correct annotation. IL21 activates JAK1/JAK3 which then phosphorylate STAT proteins. IL21 POSITIVELY REGULATES this process but does not catalyze it directly. This is the correct term to use.
Supporting Evidence:
PMID:17673207
Epub 2007 Jul 25. Cloning and characterization of an isoform of interleukin-21.
GO:0005576 extracellular region
TAS
Reactome:R-HSA-9005980 		KEEP AS NON CORE
Summary: Reactome pathway reference for IL21 binding to IL21R. Confirms secreted nature of IL21. Duplicate with other extracellular region annotations.
GO:0005576 extracellular region
TAS
Reactome:R-HSA-9006844 		KEEP AS NON CORE
Summary: Reactome pathway reference. Duplicate annotation.
GO:0005576 extracellular region
TAS
Reactome:R-HSA-9006850 		KEEP AS NON CORE
Summary: Reactome pathway reference. Duplicate annotation.
GO:0005576 extracellular region
TAS
Reactome:R-HSA-9006870 		KEEP AS NON CORE
Summary: Reactome pathway reference. Duplicate annotation.
GO:0005576 extracellular region
TAS
Reactome:R-HSA-9006873 		KEEP AS NON CORE
Summary: Reactome pathway reference. Duplicate annotation.
GO:0008284 positive regulation of cell population proliferation
IDA
PMID:17673207
Cloning and characterization of an isoform of interleukin-21... 		KEEP AS NON CORE
Summary: General term. IL21 promotes proliferation of specific cell types (B cells, T cells, NK cells). More specific terms are available. Keep as supporting annotation.
Supporting Evidence:
PMID:17673207
Epub 2007 Jul 25. Cloning and characterization of an isoform of interleukin-21.
GO:0030890 positive regulation of B cell proliferation
IDA
PMID:17673207
Cloning and characterization of an isoform of interleukin-21... 		ACCEPT
Summary: Specific and correct annotation. IL21 promotes B cell proliferation as part of its role in humoral immunity. Core function.
Supporting Evidence:
PMID:17673207
Epub 2007 Jul 25. Cloning and characterization of an isoform of interleukin-21.
GO:0042102 positive regulation of T cell proliferation
IDA
PMID:17673207
Cloning and characterization of an isoform of interleukin-21... 		ACCEPT
Summary: Correct annotation. IL21 promotes T cell proliferation. Core function in adaptive immunity.
Supporting Evidence:
PMID:17673207
Epub 2007 Jul 25. Cloning and characterization of an isoform of interleukin-21.
GO:0007260 tyrosine phosphorylation of STAT protein
IDA
PMID:12244150
IL-21 up-regulates the expression of genes associated with i... 		MODIFY
Summary: OVER-ANNOTATION: IL21 is a cytokine that INDUCES STAT phosphorylation via the JAK-STAT signaling pathway, but does NOT catalyze the phosphorylation reaction itself. PMID:12244150 states IL-21 "induced STAT3 activation" - the cytokine triggers downstream JAK kinases (JAK1/JAK3) to phosphorylate STAT proteins. IL21 has no kinase activity. The appropriate term is GO:0042531 "positive regulation of tyrosine phosphorylation of STAT protein" which correctly describes the regulatory role. Note IL21 already has the correct annotation at GO:0042531 (IDA, PMID:17673207).
Supporting Evidence:
PMID:12244150
IL-21 up-regulates the expression of genes associated with innate immunity and Th1 response.
GO:0045954 positive regulation of natural killer cell mediated cytotoxicity
IDA
PMID:18005035
Interleukin-21 activates human natural killer cells and modu... 		ACCEPT
Summary: Correct annotation with experimental evidence. IL21 activates NK cells and modulates their cytotoxic activity. Core function.
Supporting Evidence:
PMID:18005035
Epub 2007 Nov 14. Interleukin-21 activates human natural killer cells and modulates their surface receptor expression.
GO:0001819 positive regulation of cytokine production
IDA
PMID:19322899
Il-21 enhances NK cell activation and cytolytic activity and... 		ACCEPT
Summary: Correct annotation. IL21 enhances cytokine production including IL-17 and IFN-gamma. Core immunoregulatory function.
Supporting Evidence:
PMID:19322899
Il-21 enhances NK cell activation and cytolytic activity and induces Th17 cell differentiation in inflammatory bowel disease.
GO:0032740 positive regulation of interleukin-17 production
IDA
PMID:16482511
Divergent effects of IL-12 and IL-23 on the production of IL... 		ACCEPT
Summary: Specific and correct annotation. IL21 promotes IL-17 production by Th17 cells. Supported by experimental evidence. Core function in Th17 biology.
Supporting Evidence:
PMID:16482511
Divergent effects of IL-12 and IL-23 on the production of IL-17 by human T cells.
GO:0034105 positive regulation of tissue remodeling
IC
PMID:16482511
Divergent effects of IL-12 and IL-23 on the production of IL... 		KEEP AS NON CORE
Summary: Inferred from context. IL21 promotes IL-17 production, which is associated with tissue remodeling in inflammatory conditions. Indirect effect, not core function.
Supporting Evidence:
PMID:16482511
Divergent effects of IL-12 and IL-23 on the production of IL-17 by human T cells.
GO:0050729 positive regulation of inflammatory response
IC
PMID:16482511
Divergent effects of IL-12 and IL-23 on the production of IL... 		KEEP AS NON CORE
Summary: Inferred from context. IL21 through IL-17 induction can promote inflammation. Context-dependent effect rather than core function.
Supporting Evidence:
PMID:16482511
Divergent effects of IL-12 and IL-23 on the production of IL-17 by human T cells.
GO:0005126 cytokine receptor binding
TAS
PMID:15546387
Biology of IL-21 and the IL-21 receptor. 		KEEP AS NON CORE
Summary: Review article citing IL21 receptor biology. IL21 binds the IL21R/IL2RG receptor complex. Equivalent to cytokine activity for functional purposes.
Supporting Evidence:
PMID:15546387
Biology of IL-21 and the IL-21 receptor.
GO:0005134 interleukin-2 receptor binding
IPI
PMID:12504082
Human IL-21 and IL-4 bind to partially overlapping epitopes ... 		KEEP AS NON CORE
Summary: IL21 binds the common gamma chain (IL2RG), which is shared with IL-2 receptor. PMID:12504082 shows IL21 and IL4 bind overlapping epitopes on gamma chain. This is mechanistically correct but could be misleading - IL21 does not bind the complete IL-2 receptor, only the shared gamma chain component.
Supporting Evidence:
PMID:12504082
Human IL-21 and IL-4 bind to partially overlapping epitopes of common gamma-chain.
GO:0005615 extracellular space
NAS
PMID:11081504
Interleukin 21 and its receptor are involved in NK cell expa... 		ACCEPT
Summary: Core localization. IL21 is a secreted cytokine located in the extracellular space where it binds to cell surface receptors. Primary reference for IL21 discovery.
Supporting Evidence:
PMID:11081504
Interleukin 21 and its receptor are involved in NK cell expansion and regulation of lymphocyte function.
GO:0032729 positive regulation of type II interferon production
NAS
PMID:15765404
Interleukin-21 enhances T-helper cell type I signaling and i... 		ACCEPT
Summary: IL21 enhances IFN-gamma production. IFN-gamma is a type II interferon. Correct annotation supported by synergy with IL15 and IL18 in IFN-gamma induction.
Supporting Evidence:
PMID:15765404
Interleukin-21 enhances T-helper cell type I signaling and interferon-gamma production in Crohn's disease.
GO:0042102 positive regulation of T cell proliferation
IDA
PMID:15207081
[Cloning and expression of human interleukin-21 cDNA in E.co... 		ACCEPT
Summary: Duplicate annotation with same term from PMID:17673207. Both show IL21 promotes T cell proliferation. Maintain consistent action.
Supporting Evidence:
PMID:15207081
AIM: To clone full length cDNA of human interleukin-21 (IL-21) and express it in E.coli.
GO:0048469 cell maturation
IDA
PMID:14635054
IL-21 induces both rapid maturation of human CD34+ cell prec... 		KEEP AS NON CORE
Summary: IL21 induces maturation of CD34+ precursors towards NK cells. Specific to NK cell development. Keep as supporting annotation.
Supporting Evidence:
PMID:14635054
IL-21 induces both rapid maturation of human CD34+ cell precursors towards NK cells and acquisition of surface killer Ig-like receptors.
GO:0007165 signal transduction
NAS
PMID:11081504
Interleukin 21 and its receptor are involved in NK cell expa... 		MARK AS OVER ANNOTATED
Summary: Very general term. All cytokines trigger signal transduction. Too broad to be informative for IL21 specifically. More specific pathway terms (JAK-STAT signaling) are more appropriate.
Supporting Evidence:
PMID:11081504
Interleukin 21 and its receptor are involved in NK cell expansion and regulation of lymphocyte function.

Core Functions

IL21 functions as a secreted cytokine, binding to the IL21R/IL2RG receptor complex on target cells (B cells, T cells, NK cells) to activate the JAK1/JAK3-STAT1/STAT3/STAT5 signaling pathway.

Molecular Function:
cytokine activity
Directly Involved In:
germinal center B cell differentiation positive regulation of immunoglobulin production T follicular helper cell differentiation positive regulation of B cell proliferation positive regulation of T cell proliferation positive regulation of natural killer cell mediated cytotoxicity
Cellular Locations:
extracellular space

References

GO_REF:0000002
Gene Ontology annotation through association of InterPro records with GO terms
GO_REF:0000024
Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity
GO_REF:0000033
Annotation inferences using phylogenetic trees
GO_REF:0000043
Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
GO_REF:0000107
Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara
GO_REF:0000117
Electronic Gene Ontology annotations created by ARBA machine learning models
GO_REF:0000120
Combined Automated Annotation using Multiple IEA Methods
PMID:11081504
Interleukin 21 and its receptor are involved in NK cell expansion and regulation of lymphocyte function.
  • IL21 discovered as a cytokine that promotes NK cell expansion and regulates lymphocyte function
PMID:12244150
IL-21 up-regulates the expression of genes associated with innate immunity and Th1 response.
  • IL-21 induced STAT3 activation in human T cells and NK cells
PMID:12504082
Human IL-21 and IL-4 bind to partially overlapping epitopes of common gamma-chain.
  • IL21 binds the common gamma chain shared with IL-2 receptor
PMID:14635054
IL-21 induces both rapid maturation of human CD34+ cell precursors towards NK cells and acquisition of surface killer Ig-like receptors.
  • IL21 induces maturation of CD34+ hematopoietic precursors into NK cells
PMID:15207081
[Cloning and expression of human interleukin-21 cDNA in E.coli].
PMID:15546387
Biology of IL-21 and the IL-21 receptor.
  • Review of IL21 biology and receptor signaling
PMID:15765404
Interleukin-21 enhances T-helper cell type I signaling and interferon-gamma production in Crohn's disease.
  • IL21 enhances IFN-gamma (type II interferon) production
PMID:16482511
Divergent effects of IL-12 and IL-23 on the production of IL-17 by human T cells.
  • IL21 promotes IL-17 production by T cells
PMID:17673207
Cloning and characterization of an isoform of interleukin-21.
  • IL21 promotes T and B cell proliferation and activates STAT phosphorylation
PMID:17938255
The opposite effects of IL-15 and IL-21 on CLL B cells correlate with differential activation of the JAK/STAT and ERK1/2 pathways.
  • IL21 activates the JAK-STAT pathway in B cells
PMID:18005035
Interleukin-21 activates human natural killer cells and modulates their surface receptor expression.
  • IL21 activates NK cells and enhances their cytotoxic activity
PMID:19322899
Il-21 enhances NK cell activation and cytolytic activity and induces Th17 cell differentiation in inflammatory bowel disease.
  • IL21 enhances NK cell cytolytic activity and promotes Th17 differentiation
PMID:28798470
Identification of the novel 3' UTR sequences of human IL-21 mRNA as potential targets of miRNAs.
PMID:32296183
A reference map of the human binary protein interactome.
PMID:37339051
A structural blueprint for interleukin-21 signal modulation.
  • Structural analysis of IL21-receptor interactions
Reactome:R-HSA-9005980
IL21 binds IL21R:JAK1
Reactome:R-HSA-9006844
IL21:IL21R:JAK1 binds IL2RG:JAK3
Reactome:R-HSA-9006850
IL21 receptor JAK phosphorylation
Reactome:R-HSA-9006870
IL21 receptor STAT phosphorylation
Reactome:R-HSA-9006873
IL21 receptor STAT binding

๐Ÿ“š Additional Documentation

Deep Research Falcon

(IL21-deep-research-falcon.md)

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gene_id: IL21
gene_symbol: IL21
uniprot_accession: Q9HBE4
protein_description: 'RecName: Full=Interleukin-21 {ECO:0000305}; Short=IL-21; AltName:
Full=Za11; Flags: Precursor;'
gene_info: Name=IL21 {ECO:0000312|HGNC:HGNC:6005};
organism_full: Homo sapiens (Human).
protein_family: Belongs to the IL-15/IL-21 family. .
protein_domains: 4_helix_cytokine-like_core. (IPR009079); IL-15/IL-21_fam. (IPR003443);
IL15 (PF02372)
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Question

Gene Research for Functional Annotation

โš ๏ธ CRITICAL: Gene/Protein Identification Context

BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.

Target Gene/Protein Identity (from UniProt):

  • UniProt Accession: Q9HBE4
  • Protein Description: RecName: Full=Interleukin-21 {ECO:0000305}; Short=IL-21; AltName: Full=Za11; Flags: Precursor;
  • Gene Information: Name=IL21 {ECO:0000312|HGNC:HGNC:6005};
  • Organism (full): Homo sapiens (Human).
  • Protein Family: Belongs to the IL-15/IL-21 family. .
  • Key Domains: 4_helix_cytokine-like_core. (IPR009079); IL-15/IL-21_fam. (IPR003443); IL15 (PF02372)

MANDATORY VERIFICATION STEPS:

  1. Check if the gene symbol "IL21" matches the protein description above
  2. Verify the organism is correct: Homo sapiens (Human).
  3. Check if protein family/domains align with what you find in literature
  4. If you find literature for a DIFFERENT gene with the same or similar symbol, STOP

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'IL21' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information

Research Target:

Please provide a comprehensive research report on the gene IL21 (gene ID: IL21, UniProt: Q9HBE4) in human.

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Output

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on:
1. Key concepts and definitions with current understanding
2. Recent developments and latest research (prioritize 2023-2024 sources)
3. Current applications and real-world implementations
4. Expert opinions and analysis from authoritative sources
5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available.
Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Gene Research for Functional Annotation

โš ๏ธ CRITICAL: Gene/Protein Identification Context

BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.

Target Gene/Protein Identity (from UniProt):

  • UniProt Accession: Q9HBE4
  • Protein Description: RecName: Full=Interleukin-21 {ECO:0000305}; Short=IL-21; AltName: Full=Za11; Flags: Precursor;
  • Gene Information: Name=IL21 {ECO:0000312|HGNC:HGNC:6005};
  • Organism (full): Homo sapiens (Human).
  • Protein Family: Belongs to the IL-15/IL-21 family. .
  • Key Domains: 4_helix_cytokine-like_core. (IPR009079); IL-15/IL-21_fam. (IPR003443); IL15 (PF02372)

MANDATORY VERIFICATION STEPS:

  1. Check if the gene symbol "IL21" matches the protein description above
  2. Verify the organism is correct: Homo sapiens (Human).
  3. Check if protein family/domains align with what you find in literature
  4. If you find literature for a DIFFERENT gene with the same or similar symbol, STOP

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'IL21' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information

Research Target:

Please provide a comprehensive research report on the gene IL21 (gene ID: IL21, UniProt: Q9HBE4) in human.

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Plan and verification
- Target verification: The UniProt entry Q9HBE4 corresponds to human interleukin-21 (IL-21), encoded by the human IL21 gene, a secreted type I cytokine in the common gamma chain (ฮณc) cytokine family with a four-helix bundle fold; it signals through IL-21R paired with the common ฮณ chain (IL2RG). This matches the provided identity, organism (Homo sapiens), and family/domain context. (spolski2014interleukin21adoubleedged pages 1-2, koh2024il17andil21 pages 2-4, zeng2007themolecularbasis pages 1-3)

1) Key concepts and definitions (current understanding)
- Identity and family: IL-21 is a pleiotropic type I cytokine of the common ฮณc cytokine family (with IL-2, IL-4, IL-7, IL-9, IL-15, IL-21) characterized structurally by a four-helix bundle fold. It is produced predominantly by CD4+ T-cell subsets, notably follicular helper T cells (Tfh) and Th17 cells, and also by NKT cells; CD8+ T cells can produce IL-21 in some contexts. (Spolski & Leonard 2014, Nat Rev Drug Discov; Koh et al. 2024, Immune Network; Isvoranu & Chiritoiu-Butnaru 2024, Front Immunol). URLs: https://doi.org/10.1038/nrd4296 (2014-04); https://doi.org/10.4110/in.2024.24.e2 (2024-01); https://doi.org/10.3389/fimmu.2024.1369743 (2024-04). (spolski2014interleukin21adoubleedged pages 1-2, koh2024il17andil21 pages 2-4, isvoranu2024therapeuticpotentialof pages 1-2)
- Receptor and signaling: IL-21 signals via a heterodimeric receptor composed of IL-21R and the common ฮณ chain (CD132), activating JAK1/JAK3 to predominantly induce STAT3 and STAT1 phosphorylation (with weaker STAT5), and also engages MAPK and PI3K/AKT pathways. Negative feedback via SOCS1/3 and transcriptional programs requiring IRF4, BATFโ€“JUN, and STAT3 are prominent. (Koh 2024; Spolski & Leonard 2014; Zeng et al. 2007, Blood). URLs: https://doi.org/10.4110/in.2024.24.e2 (2024-01); https://doi.org/10.1038/nrd4296 (2014-04); https://doi.org/10.1182/blood-2006-10-054973 (2007-05). (koh2024il17andil21 pages 6-7, spolski2014interleukin21adoubleedged pages 1-2, zeng2007themolecularbasis pages 1-3)
- Cellular localization: IL-21 is secreted and acts in a paracrine/autocrine manner on lymphoid and myeloid cells expressing IL-21R. (Spolski & Leonard 2014; Koh 2024). URL: https://doi.org/10.1038/nrd4296; https://doi.org/10.4110/in.2024.24.e2. (spolski2014interleukin21adoubleedged pages 1-2, koh2024il17andil21 pages 2-4)

2) Mechanistic functions and pathways (cell-type specific)
- B cells: IL-21 is pivotal for germinal center (GC) responses. It promotes isotype class switching (notably IgG subclasses), plasma cell differentiation, and long-lived antibody responses via STAT3- and IRF4-dependent induction of BLIMP-1/PRDM1; IL-21R deficiency impairs expansion of antigen-specific memory B cells and plasma cells and skews Ig isotypes (e.g., reduced IgG with elevated IgE in IL-4โ€“rich contexts). IL-21 can also induce B-cell apoptosis depending on context. URLs: https://doi.org/10.4110/in.2024.24.e2; https://doi.org/10.1038/nrd4296. (koh2024il17andil21 pages 7-9, spolski2014interleukin21adoubleedged pages 1-2)
- CD4+ T cells and T helper programming: IL-21 serves as an autocrine factor for Th17 differentiation (with TGF-ฮฒ), supports Tfh lineage programs, and can promote Th1 features in human cells under some conditions (e.g., increased STAT4/T-bet and IFN-ฮณ in Crohnโ€™s lamina propria). It modulates Treg/tr1 biology: Il21 deficiency can increase Treg numbers, whereas IL-21 can also promote IL-10โ€“producing Tr1 cells depending on milieu. URL: https://doi.org/10.4110/in.2024.24.e2. (koh2024il17andil21 pages 6-7, koh2024il17andil21 pages 7-9)
- CD8+ T cells: IL-21 synergizes with IL-7/IL-15 (and IL-2) to drive CD8+ proliferation, cytotoxic differentiation, IFN-ฮณ production, and memory-like persistence, enhancing antitumor responses. URLs: https://doi.org/10.4110/in.2024.24.e2; https://doi.org/10.1182/blood-2006-10-054973. (koh2024il17andil21 pages 7-9, zeng2007themolecularbasis pages 1-3)
- NK cells: IL-21 activates human NK cells, boosting cytotoxicity (including synergy with IL-15/IL-18) and reinvigorating exhausted NK cells in tumors, although context-dependent inhibitory effects are reported. URLs: https://doi.org/10.4110/in.2024.24.e2. (koh2024il17andil21 pages 7-9, koh2024il17andil21 pages 19-20)
- Dendritic cells and myeloid cells: IL-21 can negatively regulate conventional dendritic cell (cDC) maturation and induce apoptosis via STAT3/BIM; it modulates monocyte/macrophage functions. URLs: https://doi.org/10.4110/in.2024.24.e2; https://doi.org/10.1038/nrd4296. (koh2024il17andil21 pages 7-9, spolski2014interleukin21adoubleedged pages 1-2)
- Intracellular signaling detail: Mutation analyses of IL-21R cytoplasmic tyrosines show Y510 is sufficient for STAT1/3 activation and full proliferative signaling; MAPK and PI3K contribute to IL-21โ€“mediated proliferation and are pharmacologically inhibitable. URL: https://doi.org/10.1182/blood-2006-10-054973. (zeng2007themolecularbasis pages 1-3)

3) Recent developments and latest research (emphasis 2023โ€“2024)
- Updated immunobiology reviews: 2024 reviews synthesize IL-21โ€™s dual (โ€œdouble-edgedโ€) roles, integrating STAT3 vs STAT1 balance, IRF4/BATF cooperation, and cell-typeโ€“specific outcomes across B cells, Tfh/Th17, CD8, NK, and DCs, with translational implications. URL: https://doi.org/10.4110/in.2024.24.e2 (2024-01). (koh2024il17andil21 pages 19-20, koh2024il17andil21 pages 6-7)
- Cancer immunotherapy positioning: 2024 review highlights IL-21 as an immunostimulatory cytokine with promising antitumor activity alone or in rational combinations (mAbs, checkpoint inhibitors, oncolytic virotherapy, adoptive cell therapies), with generally manageable toxicity in early trials. URL: https://doi.org/10.3389/fimmu.2024.1369743 (2024-04). (isvoranu2024therapeuticpotentialof pages 1-2)
- Mechanistic oncology updates: IL-21 can reshape tumor-infiltrating lymphocytes (e.g., expansion of favorable CD8+ subsets) and act via NK-mediated mechanisms, underscoring context-dependent pro- versus antitumor effects. URL: https://doi.org/10.4110/in.2024.24.e2 (2024-01). (koh2024il17andil21 pages 22-23)

4) Disease associations and mechanisms (selected, with recent sources)
- Autoimmunity and inflammation: Elevated IL-21 or IL-21R signaling is associated with inflammatory bowel disease (e.g., Crohnโ€™s), SLE (autoreactive CD11chi T-bet+ B cells), and psoriasis; neutralization or pathway modulation affects Th1/Th17 polarization and inflammatory mediators in human tissues and models. URL: https://doi.org/10.4110/in.2024.24.e2 (2024-01). (koh2024il17andil21 pages 22-23)
- Infection and mucosal immunity: IL-21 participates in mucosal Th1 responses (e.g., coeliac disease, IBD) and antiviral antibody responses in infection and vaccination contexts, supporting Tfh and GC reactions. URL: https://doi.org/10.4110/in.2024.24.e2 (2024-01). (koh2024il17andil21 pages 19-20, koh2024il17andil21 pages 22-23)
- Oncology: IL-21 supports antitumor CD8 and NK activity, can induce apoptosis and enhance ADCC in B-cell malignancies (e.g., CLL), but may have protumor roles depending on microenvironmental STAT utilization and cellular targets. URLs: https://doi.org/10.4110/in.2024.24.e2 (2024-01); https://doi.org/10.3389/fimmu.2024.1369743 (2024-04). (koh2024il17andil21 pages 22-23, isvoranu2024therapeuticpotentialof pages 1-2)

5) Current applications and implementations
- Recombinant IL-21 in oncology: Early clinical studies have evaluated recombinant IL-21 as monotherapy or in combination with antibodies and checkpoint inhibitors, with reported antitumor activity and generally tolerable safety in phase I/II settings, per 2024 review synthesis. URL: https://doi.org/10.3389/fimmu.2024.1369743 (2024-04). (isvoranu2024therapeuticpotentialof pages 1-2)
- Pathway antagonism in autoimmunity: Development of therapeutic antagonists targeting IL-21 or IL-21R has been pursued for RA, SLE, and Crohnโ€™s disease; earlier clinical evaluations are summarized in foundational reviews. URL: https://doi.org/10.1038/nrd4296 (2014-04). (spolski2014interleukin21adoubleedged pages 1-2)
- JAK pathway inhibition: Because IL-21 signals through JAK1/JAK3โ†’STAT3/STAT1, approved JAK inhibitors can modulate IL-21โ€“driven biology indirectly; this is mechanistically grounded in the canonical pathway description. URLs: https://doi.org/10.4110/in.2024.24.e2; https://doi.org/10.1182/blood-2006-10-054973. (koh2024il17andil21 pages 6-7, zeng2007themolecularbasis pages 1-3)
- Cellular therapies and combinations: Reviews highlight IL-21โ€™s integration into adoptive cell strategies (e.g., for supporting CD8/NK function) and in combination regimens including oncolytic virotherapy; these are active translational areas with ongoing early-phase testing. URL: https://doi.org/10.3389/fimmu.2024.1369743 (2024-04). (isvoranu2024therapeuticpotentialof pages 1-2)

6) Expert opinions and analysis from authoritative sources
- Consensus across high-quality reviews emphasizes IL-21 as a central Tfh- and Th17-derived cytokine orchestrating humoral immunity and cytotoxic effector programming, with outcomes determined by cellular context and STAT3/STAT1 balance. Therapeutically, IL-21 can be leveraged to boost antitumor immunity, while antagonism may be beneficial in autoimmunity. URLs: https://doi.org/10.1038/nrd4296; https://doi.org/10.4110/in.2024.24.e2; https://doi.org/10.3389/fimmu.2024.1369743. (spolski2014interleukin21adoubleedged pages 1-2, koh2024il17andil21 pages 19-20, isvoranu2024therapeuticpotentialof pages 1-2)

7) Relevant statistics and quantitative data
- Specific recent (2023โ€“2024) trial effect sizes and patient-level statistics could not be extracted from the accessible source excerpts. However, early oncology trials summarized in 2024 review literature report antitumor activity with generally minimal or manageable adverse events for recombinant IL-21 alone or in combinations. Additional quantitative details would require direct access to individual trial reports. URL: https://doi.org/10.3389/fimmu.2024.1369743 (2024-04). (isvoranu2024therapeuticpotentialof pages 1-2)

8) Summary functional annotation (precise role and localization)
- Molecule type: Secreted cytokine (four-helix bundle) of the ฮณc family. Receptor: IL-21R/ฮณc heterodimer. Primary signaling: JAK1/JAK3โ†’STAT3>STAT1 (ยฑSTAT5), with MAPK and PI3K/AKT contributions; SOCS1/3 negative feedback; IRF4, BATFโ€“JUN, and STAT3 transcriptional modules. Producers: Tfh, Th17, NKT (and contextually CD8+ T cells). Targets: B, T, NK, DCs, and other hematopoietic cells expressing IL-21R. Cellular location of action: Extracellular (secreted), acting on immune cell surfaces bearing IL-21R. Primary functions: Orchestrates GC B-cell help (class switching, plasma-cell differentiation), sustains and programs CD8 and NK cytotoxicity, shapes Th subset balance, and modulates DC maturation. Pathway role: Central node in adaptive immunity with context-dependent roles in infection, autoimmunity, and cancer. URLs: https://doi.org/10.1038/nrd4296; https://doi.org/10.4110/in.2024.24.e2; https://doi.org/10.3389/fimmu.2024.1369743; https://doi.org/10.1182/blood-2006-10-054973. (spolski2014interleukin21adoubleedged pages 1-2, koh2024il17andil21 pages 6-7, isvoranu2024therapeuticpotentialof pages 1-2, zeng2007themolecularbasis pages 1-3)

Notes on evidence scope and limitations
- Where 2023โ€“2024 primary studies (e.g., checkpoint inhibitor thyroiditis, single-cell plasma-cell dynamics, engineered IL-21 therapeutics) are highly relevant, detailed quantitative outcomes were not retrievable from the excerpts available to this analysis. The mechanistic and translational summaries here are therefore grounded primarily in a 2024 immunobiology review and a 2024 oncology-focused review, complemented by a seminal mechanistic study and a comprehensive 2014 review. Further specificity (trial IDs, dosing, response rates) would require direct citation of the individual primary trials or more detailed review sections. (koh2024il17andil21 pages 19-20, isvoranu2024therapeuticpotentialof pages 1-2, spolski2014interleukin21adoubleedged pages 1-2, zeng2007themolecularbasis pages 1-3)

References

  1. (spolski2014interleukin21adoubleedged pages 1-2): Rosanne Spolski and Warren J. Leonard. Interleukin-21: a double-edged sword with therapeutic potential. Nature Reviews Drug Discovery, 13:379-395, Apr 2014. URL: https://doi.org/10.1038/nrd4296, doi:10.1038/nrd4296. This article has 658 citations and is from a highest quality peer-reviewed journal.

  2. (koh2024il17andil21 pages 2-4): Choong-Hyun Koh, Byung-Seok Kim, Chang-Yuil Kang, Yeonseok Chung, and Hyungseok Seo. Il-17 and il-21: their immunobiology and therapeutic potentials. Immune Network, Jan 2024. URL: https://doi.org/10.4110/in.2024.24.e2, doi:10.4110/in.2024.24.e2. This article has 36 citations.

  3. (zeng2007themolecularbasis pages 1-3): Rong Zeng, Rosanne Spolski, Esther Casas, Wei Zhu, David E. Levy, and Warren J. Leonard. The molecular basis of il-21-mediated proliferation. Blood, 109 10:4135-42, May 2007. URL: https://doi.org/10.1182/blood-2006-10-054973, doi:10.1182/blood-2006-10-054973. This article has 403 citations and is from a highest quality peer-reviewed journal.

  4. (isvoranu2024therapeuticpotentialof pages 1-2): Gheorghita Isvoranu and Marioara Chiritoiu-Butnaru. Therapeutic potential of interleukin-21 in cancer. Frontiers in Immunology, Apr 2024. URL: https://doi.org/10.3389/fimmu.2024.1369743, doi:10.3389/fimmu.2024.1369743. This article has 23 citations and is from a peer-reviewed journal.

  5. (koh2024il17andil21 pages 6-7): Choong-Hyun Koh, Byung-Seok Kim, Chang-Yuil Kang, Yeonseok Chung, and Hyungseok Seo. Il-17 and il-21: their immunobiology and therapeutic potentials. Immune Network, Jan 2024. URL: https://doi.org/10.4110/in.2024.24.e2, doi:10.4110/in.2024.24.e2. This article has 36 citations.

  6. (koh2024il17andil21 pages 7-9): Choong-Hyun Koh, Byung-Seok Kim, Chang-Yuil Kang, Yeonseok Chung, and Hyungseok Seo. Il-17 and il-21: their immunobiology and therapeutic potentials. Immune Network, Jan 2024. URL: https://doi.org/10.4110/in.2024.24.e2, doi:10.4110/in.2024.24.e2. This article has 36 citations.

  7. (koh2024il17andil21 pages 19-20): Choong-Hyun Koh, Byung-Seok Kim, Chang-Yuil Kang, Yeonseok Chung, and Hyungseok Seo. Il-17 and il-21: their immunobiology and therapeutic potentials. Immune Network, Jan 2024. URL: https://doi.org/10.4110/in.2024.24.e2, doi:10.4110/in.2024.24.e2. This article has 36 citations.

  8. (koh2024il17andil21 pages 22-23): Choong-Hyun Koh, Byung-Seok Kim, Chang-Yuil Kang, Yeonseok Chung, and Hyungseok Seo. Il-17 and il-21: their immunobiology and therapeutic potentials. Immune Network, Jan 2024. URL: https://doi.org/10.4110/in.2024.24.e2, doi:10.4110/in.2024.24.e2. This article has 36 citations.

Citations

  1. zeng2007themolecularbasis pages 1-3
  2. isvoranu2024therapeuticpotentialof pages 1-2
  3. https://doi.org/10.1038/nrd4296
  4. https://doi.org/10.4110/in.2024.24.e2
  5. https://doi.org/10.3389/fimmu.2024.1369743
  6. https://doi.org/10.1182/blood-2006-10-054973
  7. https://doi.org/10.1038/nrd4296;
  8. https://doi.org/10.4110/in.2024.24.e2.
  9. https://doi.org/10.4110/in.2024.24.e2;
  10. https://doi.org/10.1038/nrd4296.
  11. https://doi.org/10.1182/blood-2006-10-054973.
  12. https://doi.org/10.3389/fimmu.2024.1369743.
  13. https://doi.org/10.3389/fimmu.2024.1369743;
  14. https://doi.org/10.1038/nrd4296,
  15. https://doi.org/10.4110/in.2024.24.e2,
  16. https://doi.org/10.1182/blood-2006-10-054973,
  17. https://doi.org/10.3389/fimmu.2024.1369743,

๐Ÿ“„ View Raw YAML

 
id: Q9HBE4
gene_symbol: IL21
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  Interleukin-21 (IL21) is a secreted cytokine with immunoregulatory activity that
  belongs
  to the IL-15/IL-21 family. IL21 promotes the transition between innate and adaptive
  immunity
  and is critical for T follicular helper (Tfh) cell generation and maintenance, germinal
  center
  formation, and B cell differentiation. It induces immunoglobulin production (IgG1,
  IgG3) in
  B cells, regulates proliferation and maturation of natural killer (NK) cells in
  synergy with
  IL15, and stimulates interferon-gamma production in T cells and NK cells. IL21 signals
  through
  a receptor complex containing IL21R and the common gamma chain (IL2RG), activating
  the JAK-STAT
  pathway (primarily JAK1/JAK3 and STAT1/STAT3/STAT5). Expressed primarily by activated
  CD4+
  T cells. Mutations cause common variable immunodeficiency 11 (CVID11).
existing_annotations:
# IBA annotations - phylogenetic inference
  - term:
      id: GO:0001819
      label: positive regulation of cytokine production
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: >-
        Phylogenetically inferred annotation supported by IL21's demonstrated role
        in cytokine
        regulation. IL21 stimulates IFN-gamma production in synergy with IL15 and
        IL18, and enhances
        IL-17 production. Consistent with experimental evidence.
      action: ACCEPT
  - term:
      id: GO:0045954
      label: positive regulation of natural killer cell mediated cytotoxicity
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: >-
        Phylogenetically inferred annotation consistent with IL21's role in NK cell
        function.
        Supported by experimental data (PMID:18005035) showing IL21 activates NK cells
        and
        modulates their cytotoxic activity.
      action: ACCEPT
# IEA annotations - automated methods
  - term:
      id: GO:0001819
      label: positive regulation of cytokine production
    evidence_type: IEA
    original_reference_id: GO_REF:0000117
    review:
      summary: >-
        ARBA-predicted annotation consistent with IL21's function. Duplicates IBA
        annotation
        with same term - maintain consistent action.
      action: ACCEPT
  - term:
      id: GO:0005125
      label: cytokine activity
    evidence_type: IEA
    original_reference_id: GO_REF:0000043
    review:
      summary: >-
        Core molecular function. IL21 is a secreted cytokine that binds to its receptor
        complex (IL21R/IL2RG) and activates downstream signaling. This is the primary
        molecular function of IL21.
      action: ACCEPT
  - term:
      id: GO:0005126
      label: cytokine receptor binding
    evidence_type: IEA
    original_reference_id: GO_REF:0000120
    review:
      summary: >-
        Correct annotation. IL21 binds the IL21 receptor complex. This is essentially
        equivalent to cytokine activity for this protein. Keep but not core since
        cytokine activity is the primary MF term.
      action: KEEP_AS_NON_CORE
  - term:
      id: GO:0005576
      label: extracellular region
    evidence_type: IEA
    original_reference_id: GO_REF:0000120
    review:
      summary: >-
        Correct general location term. IL21 is secreted. More specific term (extracellular
        space) is also annotated. Keep as supporting annotation.
      action: KEEP_AS_NON_CORE
  - term:
      id: GO:0005615
      label: extracellular space
    evidence_type: IEA
    original_reference_id: GO_REF:0000043
    review:
      summary: >-
        Duplicates NAS annotation from PMID:11081504. More specific than extracellular
        region.
        Maintain consistent action with curated annotation.
      action: ACCEPT
  - term:
      id: GO:0006952
      label: defense response
    evidence_type: IEA
    original_reference_id: GO_REF:0000117
    review:
      summary: >-
        Very general term. IL21 does participate in immune defense but more specific
        terms
        (defense response to virus) are available. Term is too general for core function.
      action: MARK_AS_OVER_ANNOTATED
  - term:
      id: GO:0006955
      label: immune response
    evidence_type: IEA
    original_reference_id: GO_REF:0000002
    review:
      summary: >-
        Very general term. All cytokine activity involves immune response. More specific
        terms are appropriate for IL21 function.
      action: MARK_AS_OVER_ANNOTATED
  - term:
      id: GO:0009615
      label: response to virus
    evidence_type: IEA
    original_reference_id: GO_REF:0000117
    review:
      summary: >-
        General term. IL21 plays a role in antiviral immunity but more specific term
        (defense response to virus, GO:0051607) is more appropriate.
      action: KEEP_AS_NON_CORE
  - term:
      id: GO:0045954
      label: positive regulation of natural killer cell mediated cytotoxicity
    evidence_type: IEA
    original_reference_id: GO_REF:0000117
    review:
      summary: >-
        Duplicates IBA/IDA annotation for same term. ARBA-predicted. Consistent with
        experimental evidence. Maintain consistent action.
      action: ACCEPT
  - term:
      id: GO:0048468
      label: cell development
    evidence_type: IEA
    original_reference_id: GO_REF:0000117
    review:
      summary: >-
        Very general term. IL21 is involved in specific cell development processes
        (NK cell, B cell, Tfh cell development) but this term is too broad. More
        specific terms should be used.
      action: MARK_AS_OVER_ANNOTATED
  - term:
      id: GO:0051251
      label: positive regulation of lymphocyte activation
    evidence_type: IEA
    original_reference_id: GO_REF:0000117
    review:
      summary: >-
        Consistent with IL21 function. IL21 promotes B cell and T cell activation.
        Relatively general but accurate for IL21's immunoregulatory role.
      action: KEEP_AS_NON_CORE
# IPI annotations - physical interaction evidence
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:32296183
    review:
      summary: >-
        NON-INFORMATIVE: protein binding is too generic. Does not describe what
        IL21 binds or the functional consequence. For a cytokine, cytokine receptor
        binding (GO:0005126) or interleukin-2 receptor binding (GO:0005134) are
        more informative.
      action: REMOVE
      supported_by:
        - reference_id: PMID:32296183
          supporting_text: Apr 8. A reference map of the human binary protein 
            interactome.
  - term:
      id: GO:0005886
      label: plasma membrane
    evidence_type: IPI
    original_reference_id: PMID:37339051
    review:
      summary: >-
        This annotation likely refers to IL21 associating with plasma membrane via
        receptor binding (IL21R is membrane-bound). However, IL21 itself is a secreted
        protein, not a membrane protein. This may be misleading - IL21 is transiently
        at the membrane when bound to receptor but its primary location is extracellular.
      action: MARK_AS_OVER_ANNOTATED
# IEA annotations from Ensembl Compara orthologs (GO_REF:0000107)
      supported_by:
        - reference_id: PMID:37339051
          supporting_text: 2023 Jun 19. A structural blueprint for 
            interleukin-21 signal modulation.
  - term:
      id: GO:0002314
      label: germinal center B cell differentiation
    evidence_type: IEA
    original_reference_id: GO_REF:0000107
    review:
      summary: >-
        Core function. IL21 is critical for germinal center formation and B cell
        differentiation. Supported by ISS annotation and mouse knockout data.
      action: ACCEPT
  - term:
      id: GO:0002639
      label: positive regulation of immunoglobulin production
    evidence_type: IEA
    original_reference_id: GO_REF:0000107
    review:
      summary: >-
        Core function. IL21 induces IgG1 and IgG3 production in B cells. This is
        one of the primary biological roles of IL21.
      action: ACCEPT
  - term:
      id: GO:0061470
      label: T follicular helper cell differentiation
    evidence_type: IEA
    original_reference_id: GO_REF:0000107
    review:
      summary: >-
        Core function. IL21 is implicated in the generation and maintenance of Tfh
        cells.
        Together with IL6, critical for effective antibody response to viral infection.
      action: ACCEPT
  - term:
      id: GO:0098586
      label: cellular response to virus
    evidence_type: IEA
    original_reference_id: GO_REF:0000107
    review:
      summary: >-
        IL21 plays a role in antiviral immunity through multiple mechanisms.
        Consistent with defense response to virus annotation. Keep as supporting.
      action: KEEP_AS_NON_CORE
# NAS annotations - non-traceable author statements
  - term:
      id: GO:0007259
      label: cell surface receptor signaling pathway via JAK-STAT
    evidence_type: NAS
    original_reference_id: PMID:17938255
    review:
      summary: >-
        IL21 signals through JAK1/JAK3 and STAT1/STAT3/STAT5. However, this term describes
        the pathway that IL21 TRIGGERS, not a process IL21 directly participates in.
        IL21 is the ligand that initiates this signaling. The annotation is reasonable
        but imprecise - IL21's role is to bind receptor and activate the pathway.
      action: KEEP_AS_NON_CORE
      supported_by:
        - reference_id: PMID:17938255
          supporting_text: Oct 15. The opposite effects of IL-15 and IL-21 on 
            CLL B cells correlate with differential activation of the JAK/STAT 
            and ERK1/2 pathways.
  - term:
      id: GO:0016064
      label: immunoglobulin mediated immune response
    evidence_type: NAS
    original_reference_id: PMID:37339051
    review:
      summary: >-
        IL21 promotes immunoglobulin production by B cells, thus indirectly supporting
        immunoglobulin-mediated immunity. However, IL21 itself does not directly participate
        in immunoglobulin-mediated immune responses - it's an upstream regulator.
      action: MARK_AS_OVER_ANNOTATED
      supported_by:
        - reference_id: PMID:37339051
          supporting_text: 2023 Jun 19. A structural blueprint for 
            interleukin-21 signal modulation.
  - term:
      id: GO:0030101
      label: natural killer cell activation
    evidence_type: NAS
    original_reference_id: PMID:37339051
    review:
      summary: >-
        Supported by experimental evidence. IL21 activates NK cells and modulates
        their surface receptor expression. Core function in NK cell biology.
      action: ACCEPT
# ISS annotations - sequence similarity
      supported_by:
        - reference_id: PMID:37339051
          supporting_text: 2023 Jun 19. A structural blueprint for 
            interleukin-21 signal modulation.
  - term:
      id: GO:0002314
      label: germinal center B cell differentiation
    evidence_type: ISS
    original_reference_id: GO_REF:0000024
    review:
      summary: >-
        Duplicates IEA annotation. Based on manual transfer from mouse ortholog.
        Core function supported by multiple evidence types. Maintain consistent action.
      action: ACCEPT
  - term:
      id: GO:0002639
      label: positive regulation of immunoglobulin production
    evidence_type: ISS
    original_reference_id: GO_REF:0000024
    review:
      summary: >-
        Duplicates IEA annotation. Based on manual transfer from mouse ortholog.
        Core function supported by multiple evidence types. Maintain consistent action.
      action: ACCEPT
  - term:
      id: GO:0061470
      label: T follicular helper cell differentiation
    evidence_type: ISS
    original_reference_id: GO_REF:0000024
    review:
      summary: >-
        Duplicates IEA annotation. Based on manual transfer from mouse ortholog.
        Core function supported by multiple evidence types. Maintain consistent action.
      action: ACCEPT
  - term:
      id: GO:0098586
      label: cellular response to virus
    evidence_type: ISS
    original_reference_id: GO_REF:0000024
    review:
      summary: >-
        Duplicates IEA annotation. Based on manual transfer from mouse ortholog.
        Consistent with IL21 antiviral role.
      action: KEEP_AS_NON_CORE
# TAS annotations - traceable author statements
  - term:
      id: GO:0051607
      label: defense response to virus
    evidence_type: TAS
    original_reference_id: PMID:28798470
    review:
      summary: >-
        IL21 contributes to antiviral immunity through multiple mechanisms including
        enhancing NK cell cytotoxicity and T cell responses. Supported by literature.
      action: ACCEPT
# IDA annotations - direct experimental assay
      supported_by:
        - reference_id: PMID:28798470
          supporting_text: Identification of the novel 3' UTR sequences of human
            IL-21 mRNA as potential targets of miRNAs.
  - term:
      id: GO:0042531
      label: positive regulation of tyrosine phosphorylation of STAT protein
    evidence_type: IDA
    original_reference_id: PMID:17673207
    review:
      summary: >-
        Correct annotation. IL21 activates JAK1/JAK3 which then phosphorylate STAT
        proteins.
        IL21 POSITIVELY REGULATES this process but does not catalyze it directly.
        This is the correct term to use.
      action: ACCEPT
# Reactome TAS annotations - extracellular region
      supported_by:
        - reference_id: PMID:17673207
          supporting_text: Epub 2007 Jul 25. Cloning and characterization of an 
            isoform of interleukin-21.
  - term:
      id: GO:0005576
      label: extracellular region
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-9005980
    review:
      summary: >-
        Reactome pathway reference for IL21 binding to IL21R. Confirms secreted
        nature of IL21. Duplicate with other extracellular region annotations.
      action: KEEP_AS_NON_CORE
  - term:
      id: GO:0005576
      label: extracellular region
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-9006844
    review:
      summary: >-
        Reactome pathway reference. Duplicate annotation.
      action: KEEP_AS_NON_CORE
  - term:
      id: GO:0005576
      label: extracellular region
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-9006850
    review:
      summary: >-
        Reactome pathway reference. Duplicate annotation.
      action: KEEP_AS_NON_CORE
  - term:
      id: GO:0005576
      label: extracellular region
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-9006870
    review:
      summary: >-
        Reactome pathway reference. Duplicate annotation.
      action: KEEP_AS_NON_CORE
  - term:
      id: GO:0005576
      label: extracellular region
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-9006873
    review:
      summary: >-
        Reactome pathway reference. Duplicate annotation.
      action: KEEP_AS_NON_CORE
# More IDA annotations
  - term:
      id: GO:0008284
      label: positive regulation of cell population proliferation
    evidence_type: IDA
    original_reference_id: PMID:17673207
    review:
      summary: >-
        General term. IL21 promotes proliferation of specific cell types (B cells,
        T cells,
        NK cells). More specific terms are available. Keep as supporting annotation.
      action: KEEP_AS_NON_CORE
      supported_by:
        - reference_id: PMID:17673207
          supporting_text: Epub 2007 Jul 25. Cloning and characterization of an 
            isoform of interleukin-21.
  - term:
      id: GO:0030890
      label: positive regulation of B cell proliferation
    evidence_type: IDA
    original_reference_id: PMID:17673207
    review:
      summary: >-
        Specific and correct annotation. IL21 promotes B cell proliferation as part
        of its role in humoral immunity. Core function.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:17673207
          supporting_text: Epub 2007 Jul 25. Cloning and characterization of an 
            isoform of interleukin-21.
  - term:
      id: GO:0042102
      label: positive regulation of T cell proliferation
    evidence_type: IDA
    original_reference_id: PMID:17673207
    review:
      summary: >-
        Correct annotation. IL21 promotes T cell proliferation. Core function in
        adaptive immunity.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:17673207
          supporting_text: Epub 2007 Jul 25. Cloning and characterization of an 
            isoform of interleukin-21.
  - term:
      id: GO:0007260
      label: tyrosine phosphorylation of STAT protein
    evidence_type: IDA
    original_reference_id: PMID:12244150
    review:
      summary: >-
        OVER-ANNOTATION: IL21 is a cytokine that INDUCES STAT phosphorylation via
        the
        JAK-STAT signaling pathway, but does NOT catalyze the phosphorylation reaction
        itself. PMID:12244150 states IL-21 "induced STAT3 activation" - the cytokine
        triggers downstream JAK kinases (JAK1/JAK3) to phosphorylate STAT proteins.
        IL21 has no kinase activity. The appropriate term is GO:0042531 "positive
        regulation of tyrosine phosphorylation of STAT protein" which correctly describes
        the regulatory role. Note IL21 already has the correct annotation at GO:0042531
        (IDA, PMID:17673207).
      action: MODIFY
      proposed_replacement_terms:
        - id: GO:0042531
          label: positive regulation of tyrosine phosphorylation of STAT protein
      supported_by:
        - reference_id: PMID:12244150
          supporting_text: IL-21 up-regulates the expression of genes associated
            with innate immunity and Th1 response.
  - term:
      id: GO:0045954
      label: positive regulation of natural killer cell mediated cytotoxicity
    evidence_type: IDA
    original_reference_id: PMID:18005035
    review:
      summary: >-
        Correct annotation with experimental evidence. IL21 activates NK cells and
        modulates their cytotoxic activity. Core function.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:18005035
          supporting_text: Epub 2007 Nov 14. Interleukin-21 activates human 
            natural killer cells and modulates their surface receptor 
            expression.
  - term:
      id: GO:0001819
      label: positive regulation of cytokine production
    evidence_type: IDA
    original_reference_id: PMID:19322899
    review:
      summary: >-
        Correct annotation. IL21 enhances cytokine production including IL-17 and
        IFN-gamma. Core immunoregulatory function.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:19322899
          supporting_text: Il-21 enhances NK cell activation and cytolytic 
            activity and induces Th17 cell differentiation in inflammatory bowel
            disease.
  - term:
      id: GO:0032740
      label: positive regulation of interleukin-17 production
    evidence_type: IDA
    original_reference_id: PMID:16482511
    review:
      summary: >-
        Specific and correct annotation. IL21 promotes IL-17 production by Th17 cells.
        Supported by experimental evidence. Core function in Th17 biology.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:16482511
          supporting_text: Divergent effects of IL-12 and IL-23 on the 
            production of IL-17 by human T cells.
  - term:
      id: GO:0034105
      label: positive regulation of tissue remodeling
    evidence_type: IC
    original_reference_id: PMID:16482511
    review:
      summary: >-
        Inferred from context. IL21 promotes IL-17 production, which is associated
        with
        tissue remodeling in inflammatory conditions. Indirect effect, not core function.
      action: KEEP_AS_NON_CORE
      supported_by:
        - reference_id: PMID:16482511
          supporting_text: Divergent effects of IL-12 and IL-23 on the 
            production of IL-17 by human T cells.
  - term:
      id: GO:0050729
      label: positive regulation of inflammatory response
    evidence_type: IC
    original_reference_id: PMID:16482511
    review:
      summary: >-
        Inferred from context. IL21 through IL-17 induction can promote inflammation.
        Context-dependent effect rather than core function.
      action: KEEP_AS_NON_CORE
      supported_by:
        - reference_id: PMID:16482511
          supporting_text: Divergent effects of IL-12 and IL-23 on the 
            production of IL-17 by human T cells.
  - term:
      id: GO:0005126
      label: cytokine receptor binding
    evidence_type: TAS
    original_reference_id: PMID:15546387
    review:
      summary: >-
        Review article citing IL21 receptor biology. IL21 binds the IL21R/IL2RG
        receptor complex. Equivalent to cytokine activity for functional purposes.
      action: KEEP_AS_NON_CORE
      supported_by:
        - reference_id: PMID:15546387
          supporting_text: Biology of IL-21 and the IL-21 receptor.
  - term:
      id: GO:0005134
      label: interleukin-2 receptor binding
    evidence_type: IPI
    original_reference_id: PMID:12504082
    review:
      summary: >-
        IL21 binds the common gamma chain (IL2RG), which is shared with IL-2 receptor.
        PMID:12504082 shows IL21 and IL4 bind overlapping epitopes on gamma chain.
        This is mechanistically correct but could be misleading - IL21 does not bind
        the complete IL-2 receptor, only the shared gamma chain component.
      action: KEEP_AS_NON_CORE
      supported_by:
        - reference_id: PMID:12504082
          supporting_text: Human IL-21 and IL-4 bind to partially overlapping 
            epitopes of common gamma-chain.
  - term:
      id: GO:0005615
      label: extracellular space
    evidence_type: NAS
    original_reference_id: PMID:11081504
    review:
      summary: >-
        Core localization. IL21 is a secreted cytokine located in the extracellular
        space
        where it binds to cell surface receptors. Primary reference for IL21 discovery.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:11081504
          supporting_text: Interleukin 21 and its receptor are involved in NK 
            cell expansion and regulation of lymphocyte function.
  - term:
      id: GO:0032729
      label: positive regulation of type II interferon production
    evidence_type: NAS
    original_reference_id: PMID:15765404
    review:
      summary: >-
        IL21 enhances IFN-gamma production. IFN-gamma is a type II interferon. Correct
        annotation supported by synergy with IL15 and IL18 in IFN-gamma induction.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:15765404
          supporting_text: Interleukin-21 enhances T-helper cell type I 
            signaling and interferon-gamma production in Crohn's disease.
  - term:
      id: GO:0042102
      label: positive regulation of T cell proliferation
    evidence_type: IDA
    original_reference_id: PMID:15207081
    review:
      summary: >-
        Duplicate annotation with same term from PMID:17673207. Both show IL21
        promotes T cell proliferation. Maintain consistent action.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:15207081
          supporting_text: 'AIM: To clone full length cDNA of human interleukin-21
            (IL-21) and express it in E.coli.'
  - term:
      id: GO:0048469
      label: cell maturation
    evidence_type: IDA
    original_reference_id: PMID:14635054
    review:
      summary: >-
        IL21 induces maturation of CD34+ precursors towards NK cells. Specific to
        NK cell development. Keep as supporting annotation.
      action: KEEP_AS_NON_CORE
      supported_by:
        - reference_id: PMID:14635054
          supporting_text: IL-21 induces both rapid maturation of human CD34+ 
            cell precursors towards NK cells and acquisition of surface killer 
            Ig-like receptors.
  - term:
      id: GO:0007165
      label: signal transduction
    evidence_type: NAS
    original_reference_id: PMID:11081504
    review:
      summary: >-
        Very general term. All cytokines trigger signal transduction. Too broad
        to be informative for IL21 specifically. More specific pathway terms
        (JAK-STAT signaling) are more appropriate.
      action: MARK_AS_OVER_ANNOTATED
      supported_by:
        - reference_id: PMID:11081504
          supporting_text: Interleukin 21 and its receptor are involved in NK
            cell expansion and regulation of lymphocyte function.
references:
  - id: GO_REF:0000002
    title: Gene Ontology annotation through association of InterPro records with
      GO terms
    findings: []
  - id: GO_REF:0000024
    title: Manual transfer of experimentally-verified manual GO annotation data 
      to orthologs by curator judgment of sequence similarity
    findings: []
  - id: GO_REF:0000033
    title: Annotation inferences using phylogenetic trees
    findings: []
  - id: GO_REF:0000043
    title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword 
      mapping
    findings: []
  - id: GO_REF:0000107
    title: Automatic transfer of experimentally verified manual GO annotation 
      data to orthologs using Ensembl Compara
    findings: []
  - id: GO_REF:0000117
    title: Electronic Gene Ontology annotations created by ARBA machine learning
      models
    findings: []
  - id: GO_REF:0000120
    title: Combined Automated Annotation using Multiple IEA Methods
    findings: []
  - id: PMID:11081504
    title: Interleukin 21 and its receptor are involved in NK cell expansion and
      regulation of lymphocyte function.
    findings:
      - statement: IL21 discovered as a cytokine that promotes NK cell expansion
          and regulates lymphocyte function
  - id: PMID:12244150
    title: IL-21 up-regulates the expression of genes associated with innate 
      immunity and Th1 response.
    findings:
      - statement: IL-21 induced STAT3 activation in human T cells and NK cells
  - id: PMID:12504082
    title: Human IL-21 and IL-4 bind to partially overlapping epitopes of common
      gamma-chain.
    findings:
      - statement: IL21 binds the common gamma chain shared with IL-2 receptor
  - id: PMID:14635054
    title: IL-21 induces both rapid maturation of human CD34+ cell precursors 
      towards NK cells and acquisition of surface killer Ig-like receptors.
    findings:
      - statement: IL21 induces maturation of CD34+ hematopoietic precursors 
          into NK cells
  - id: PMID:15207081
    title: '[Cloning and expression of human interleukin-21 cDNA in E.coli].'
    findings: []
  - id: PMID:15546387
    title: Biology of IL-21 and the IL-21 receptor.
    findings:
      - statement: Review of IL21 biology and receptor signaling
  - id: PMID:15765404
    title: Interleukin-21 enhances T-helper cell type I signaling and 
      interferon-gamma production in Crohn's disease.
    findings:
      - statement: IL21 enhances IFN-gamma (type II interferon) production
  - id: PMID:16482511
    title: Divergent effects of IL-12 and IL-23 on the production of IL-17 by 
      human T cells.
    findings:
      - statement: IL21 promotes IL-17 production by T cells
  - id: PMID:17673207
    title: Cloning and characterization of an isoform of interleukin-21.
    findings:
      - statement: IL21 promotes T and B cell proliferation and activates STAT 
          phosphorylation
  - id: PMID:17938255
    title: The opposite effects of IL-15 and IL-21 on CLL B cells correlate with
      differential activation of the JAK/STAT and ERK1/2 pathways.
    findings:
      - statement: IL21 activates the JAK-STAT pathway in B cells
  - id: PMID:18005035
    title: Interleukin-21 activates human natural killer cells and modulates 
      their surface receptor expression.
    findings:
      - statement: IL21 activates NK cells and enhances their cytotoxic activity
  - id: PMID:19322899
    title: Il-21 enhances NK cell activation and cytolytic activity and induces 
      Th17 cell differentiation in inflammatory bowel disease.
    findings:
      - statement: IL21 enhances NK cell cytolytic activity and promotes Th17 
          differentiation
  - id: PMID:28798470
    title: Identification of the novel 3' UTR sequences of human IL-21 mRNA as 
      potential targets of miRNAs.
    findings: []
  - id: PMID:32296183
    title: A reference map of the human binary protein interactome.
    findings: []
  - id: PMID:37339051
    title: A structural blueprint for interleukin-21 signal modulation.
    findings:
      - statement: Structural analysis of IL21-receptor interactions
  - id: Reactome:R-HSA-9005980
    title: IL21 binds IL21R:JAK1
    findings: []
  - id: Reactome:R-HSA-9006844
    title: IL21:IL21R:JAK1 binds IL2RG:JAK3
    findings: []
  - id: Reactome:R-HSA-9006850
    title: IL21 receptor JAK phosphorylation
    findings: []
  - id: Reactome:R-HSA-9006870
    title: IL21 receptor STAT phosphorylation
    findings: []
  - id: Reactome:R-HSA-9006873
    title: IL21 receptor STAT binding
    findings: []
core_functions:
  - molecular_function:
      id: GO:0005125
      label: cytokine activity
    description: >-
      IL21 functions as a secreted cytokine, binding to the IL21R/IL2RG receptor complex
      on target cells (B cells, T cells, NK cells) to activate the JAK1/JAK3-STAT1/STAT3/STAT5
      signaling pathway.
    directly_involved_in:
      - id: GO:0002314
        label: germinal center B cell differentiation
      - id: GO:0002639
        label: positive regulation of immunoglobulin production
      - id: GO:0061470
        label: T follicular helper cell differentiation
      - id: GO:0030890
        label: positive regulation of B cell proliferation
      - id: GO:0042102
        label: positive regulation of T cell proliferation
      - id: GO:0045954
        label: positive regulation of natural killer cell mediated cytotoxicity
    locations:
      - id: GO:0005615
        label: extracellular space