Inter-alpha-trypsin inhibitor heavy chain (ITIH)

Inter-alpha-trypsin inhibitor (IAI) heavy chains (ITIH) are a family of plasma proteins, including ITIH1 through ITIH5, that are essential for the structural integrity of the extracellular matrix (ECM) and the regulation of systemic inflammation (UniProt, 2023). These proteins are unique in their ability to form covalent bonds with hyaluronan (HA) through a trans-esterification reaction, resulting in heavy chain-hyaluronan (HC-HA) complexes that stabilize tissues and modulate leukocyte adhesion (Lord et al., 2020, J. Biol. Chem.). In clinical settings, IAI heavy chains serve as critical negative acute-phase proteins; their levels drop precipitously during severe sepsis and systemic inflammatory response syndrome (SIRS), which is strongly associated with poor patient outcomes (Lim et al., 2003, J. Infect. Dis.). Therapeutic strategies involving IAI-enriched concentrates aim to replenish these levels to inhibit excessive protease activity and restore ECM homeostasis (Opal et al., 2007, Crit. Care Med.). Furthermore, specific heavy chains like ITIH5 function as tumor suppressors, and their epigenetic silencing is a recognized biomarker for progression and metastasis in breast and colon cancers (Rose et al., 2010, Am. J. Pathol.). Drugs like Ulinastatin, which contains the light chain component of the IAI complex, are already utilized to treat acute inflammatory conditions by leveraging these protease-inhibitory properties (Pugia et al., 2007, Adv. Clin. Chem.).

Other names

Inter-alpha-inhibitor heavy chainIAI heavy chainITIH1ITIH2ITIH3ITIH4ITIH5Serum-derived hyaluronan-associated proteinSHAP

Covalent binding to hyaluronan to stabilize the extracellular matrix and inhibition of systemic inflammatory proteases such as elastase and cathepsin G.