| Aspect | Key points | Quantitative/statistical details | Primary source (include DOI URL + year) |
|---|---|---|---|
| ITIH2/HC2 identity in the IαI family | Human ITIH2 encodes heavy chain 2 (HC2) of the inter-α-trypsin inhibitor (IαI) family; hepatocyte-derived serum complexes contain bikunin plus heavy chains, and HC1/HC2 are the major heavy chains in classical human IαI. HC2 is linked to bikunin through a chondroitin sulfate chain and is not the protease-inhibitory moiety; that activity resides in bikunin. (pqac-00000012, pqac-00000014) | IαI complexes are ~225 kDa and circulate in blood at ~0.15–0.5 mg/mL; serum concentration also reported as ~0.5 mg/mL in reproductive/ECM literature. (pqac-00000012, pqac-00000017) | Zhang et al., 2024, https://doi.org/10.3389/fmed.2024.1432224; Xu et al., 2024, https://doi.org/10.3390/cancers16101907; Nagyova et al., 2024, https://doi.org/10.2478/enr-2024-0020 |
| HC2 transfer to hyaluronan via TSG-6 | HC2 is transferred from IαI to hyaluronan (HA) by TSG-6/TNFAIP6 through sequential ester-exchange/transesterification reactions involving a covalent HC2•TSG-6 intermediate, generating HC•HA (SHAP-HA) complexes that stabilize HA-rich extracellular matrices. Calcium ions assist this process; TSG-6 can act as the catalytic transferase. (pqac-00000012, pqac-00000014, pqac-00000016) | Minimum HA acceptor length for HC transfer is an octasaccharide; chemically modified HA tetra- and hexa-saccharides can also become substrates in some settings. Expected HC1 and HC2 transfer can be approximately equal depending on which HC•TSG-6 intermediate forms. (pqac-00000016) | Day, 2024, https://doi.org/10.1002/pgr2.70007; Zhang et al., 2024, https://doi.org/10.3389/fmed.2024.1432224; Xu et al., 2024, https://doi.org/10.3390/cancers16101907 |
| Localization | ITIH2/HC2 is produced mainly in liver, secreted into plasma as part of IαI, then functions extracellularly after transfer onto locally synthesized HA in tissues/ECM. HC2-containing HC•HA complexes are found in extracellular matrices and can be remodeled post-synthetically by proteolysis. (pqac-00000012, pqac-00000015, pqac-00000017) | Blood concentration of IαI family proteins: ~0.15–0.5 mg/mL or ~0.5 mg/mL depending on source/review context. HC2 can be proteolytically removed from HC•HA by ADAMTS5 and MMP7 in arthritis synovial fluid. (pqac-00000012, pqac-00000015, pqac-00000017) | Zhang et al., 2024, https://doi.org/10.3389/fmed.2024.1432224; Day, 2024, https://doi.org/10.1002/pgr2.70007; Nagyova et al., 2024, https://doi.org/10.2478/enr-2024-0020 |
| ECM structural role | The best-established function of HC2 is structural: covalent HA modification/crosslinking that stabilizes extracellular matrix architecture, affects HA organization, and can modulate cell adhesion/rolling through effects on CD44-containing matrices. (pqac-00000012, pqac-00000014, pqac-00000016) | No direct catalytic turnover number reported in provided sources; mechanistic quantitative detail available is HA octasaccharide minimum substrate size for HC transfer. (pqac-00000016) | Day, 2024, https://doi.org/10.1002/pgr2.70007; Zhang et al., 2024, https://doi.org/10.3389/fmed.2024.1432224; Xu et al., 2024, https://doi.org/10.3390/cancers16101907 |
| Physiological context: ovulation/cumulus expansion | In preovulatory follicles, serum-derived HC2 (with HC1/HC3) becomes covalently attached to cumulus-cell HA, helping build the expanded HA-rich oocyte-cumulus extracellular matrix required for ovulation and fertilization. This matrix also involves TNFAIP6/TSG-6, PTX3, versican, and bikunin. (pqac-00000007, pqac-00000008, pqac-00000017, pqac-00000018) | Mouse OCC proteomics produced >24,000 mass spectra and identified 711 proteins; ITIH1, ITIH2, ITIH3, PTX3, TNFAIP6, VCAN, and VTN were among the seven especially abundant expansion-related components. At least 34 bikunin target genes were identified in earlier reproductive studies. (pqac-00000008, pqac-00000017) | Nagyova et al., 2024, https://doi.org/10.2478/enr-2024-0020 |
| Figure-supported mechanism | A recent schematic depicts liver synthesis of IαI, circulation to the follicle, and covalent binding of heavy chains to HA in vivo; the in vitro panel shows serum dependence for retaining/stabilizing the HA matrix around the oocyte-cumulus complex. (pqac-00000018) | Qualitative schematic support; no additional numeric statistic in figure extraction. (pqac-00000018) | Nagyova et al., 2024, https://doi.org/10.2478/enr-2024-0020 |
| Human reproductive biomarker/proteomics finding (2024) | In human follicular fluid from IVF/ICSI patients, ITIH2 was among proteins upregulated in follicles yielding higher-quality day-3 embryos, consistent with a role in HA-rich cumulus/follicular matrix biology. (pqac-00000009) | Study analyzed 22 follicular-fluid samples from 19 women; 558 proteins identified; 50 differentially expressed proteins total (32 upregulated, 18 downregulated) using >1.20-fold or <0.67-fold and P<0.05 thresholds. ITIH2 was reported as upregulated in the high-quality embryo group. (pqac-00000009) | Ji et al., 2024, https://doi.org/10.1007/s43032-023-01293-x |
| Human pregnancy biomarker finding (LOPE) | Maternal plasma proteomics found ITIH2 perturbed specifically in late-onset preeclampsia (LOPE), not early-onset preeclampsia in validation, supporting disease-context-specific regulation. (pqac-00000010) | Validation logFC for ITIH2 in LOPE vs healthy pregnancy: 0.37228745; FDR in discovery table: 0.03; validation p=0.005. (pqac-00000010) | Chen et al., 2022, https://doi.org/10.1038/s41598-022-20658-x |
| Human thrombo-inflammation association | Plasma/platelet multi-omics in gestational hypertension and preeclampsia implicated ITIH2 (with ITIH3) as likely mediators of thrombo-inflammation rather than simple background markers. (pqac-00000013) | Clinical context statistic: preeclampsia complicates up to 8% of pregnancies; diagnostic thresholds noted as >140/90 mmHg and proteinuria ≥300 mg/24 h. Specific ITIH2 fold-change was not given in the excerpt. (pqac-00000013) | de Almeida et al., 2022, https://doi.org/10.3390/cells11081256 |
| Disease/biomarker review summary for ITIH2 | Review-level synthesis reports multiple human disease associations for ITIH2, including reduced serum levels in pediatric multiple sclerosis, pancreatic cancer diagnosis, diabetic retinopathy-associated vitreous changes, and osteoarticular tuberculosis diagnosis; these are associations, not proof of primary molecular function. (pqac-00000011) | Pancreatic cancer vs chronic pancreatitis AUC=0.947; osteoarticular tuberculosis AUC=0.7167 (95% CI 0.5846–0.8487). Breast-cancer estrogen receptor association reported as p=0.001 elsewhere in the review. (pqac-00000011, pqac-00000005) | Zhang et al., 2024, https://doi.org/10.3389/fmed.2024.1432224 |
| Cancer-related functional interpretation | ITIH2 is described as increasing intercellular adhesion, suppressing proliferation, and limiting glioblastoma invasion, potentially via reduced PI3K/AKT signaling; this aligns with an ECM-stabilizing/tumor-suppressive interpretation rather than enzyme activity. (pqac-00000011, pqac-00000005) | Review cites breast-cancer correlation with estrogen receptor expression at p=0.001; no direct effect size for PI3K/AKT reduction provided in excerpt. (pqac-00000011, pqac-00000005) | Zhang et al., 2024, https://doi.org/10.3389/fmed.2024.1432224 |


*Table: This table summarizes the core molecular role of human ITIH2/HC2 in the inter-alpha-inhibitor system, its extracellular localization and HA-transfer mechanism, and recent clinical/proteomic findings with quantitative details where available. It is useful as a compact evidence map linking biochemical function to physiological and disease contexts.*