The biological function and significance of CD74 in immune diseases.

CD74 (MHC class II invariant chain, Ii) is a non-polymorphic type II transmembrane glycoprotein. It is clear that, in addition to be an MHC class II chaperone, CD74 has a diversity of biological functions in physiological and pathological situations. CD74 also participates in other non-MHC II protein trafficking, such as angiotensin II type I receptor. In addition, CD74 is a cell membrane high-affinity receptor for macrophage migration inhibitory factor (MIF), D-dopachrome tautomerase (D-DT/MIF-2) and bacterial proteins. CD74 also regulates T-cell and B-cell developments, dendritic cell (DC) motility, macrophage inflammation, and thymic selection. The activation of receptor complex CD74/CD44 may lead to multiple intracellular signal pathways, such as the activation of the extracellular signal regulated kinase (ERK) 1 and 2, the PI3K-Akt signal transduction cascade, NFκB, and the AMP-activated protein kinase (AMPK) pathway. CD74 plays important roles in many inflammatory diseases, such as liver fibrosis, type I diabetes, systemic lupus erythematosus, and Alzheimer disease. In this study, we will focus on the immunological functions of CD74 molecules and its roles in immune-relevant disorders.