Major histocompatibility complex class II I-Ab (I-Ab)

Major histocompatibility complex class II I-Ab (MHC class II I-Ab) is a heterodimeric cell surface glycoprotein that plays a pivotal role in the adaptive immune system of mice, particularly those of the H-2b haplotype like the C57BL/6 strain (UniProt P01921, P04224). It is composed of an alpha chain (H2-Aa) and a beta chain (H2-Ab1) which together form a groove for binding and presenting exogenous peptide antigens to CD4+ T helper cells (NIH Gene ID 14961). This presentation is a critical step in the activation of T cells and the subsequent orchestration of the immune response against extracellular pathogens. In biomedical research, I-Ab is a major target for studying the mechanisms of antigen presentation and is central to mouse models of human diseases, such as experimental autoimmune encephalomyelitis (EAE) for multiple sclerosis, where it presents self-antigens like myelin oligodendrocyte glycoprotein (MOG). While primarily a research target, it is targeted by various research-grade monoclonal antibodies and is the focus of experimental peptide-based vaccines and immunotherapies designed to modulate T cell activity.

Other names

H2-Ab1H2-AaI-A^bAbetaIa-2H-2AbI-AbetaMHC class II I-A beta chainHistocompatibility 2, class II antigen A, beta 1

Presentation of exogenous peptides to T cell receptors (TCRs) to initiate adaptive immune responses; blockade of the peptide-binding groove by therapeutic antibodies or competitive peptides; induction of surface expression by pro-inflammatory cytokines like interferon-gamma.