Major Histocompatibility Complex class II (MHC II) and associated antigen processing machinery (MHC II)

Major Histocompatibility Complex class II (MHC II) molecules are essential cell surface glycoproteins primarily expressed on professional antigen-presenting cells (APCs) such as dendritic cells, B cells, and macrophages (StatPearls, 2023). Their primary biological function is to present processed exogenous peptides to CD4+ T helper cells, thereby orchestrating the adaptive immune response (UniProt, 2024). The associated antigen processing machinery includes the invariant chain (CD74), which prevents premature peptide binding, and HLA-DM, which catalyzes the exchange of the CLIP peptide for high-affinity antigenic fragments (PubMed, PMID: 22407918). In disease states, aberrant MHC II expression is a hallmark of autoimmune conditions like rheumatoid arthritis and multiple sclerosis, while its downregulation in tumors facilitates immune evasion (Nature Reviews Immunology, 2018). Therapeutic interventions targeting this pathway include peptide mimetics like Glatiramer acetate that compete for the binding groove, and inhibitors of processing enzymes like Cathepsin S (DrugBank, DB00644).

Other names

HLA class IIHuman Leukocyte Antigen class IIMHC-IIHLA-DRHLA-DQHLA-DPCD74Invariant chainHLA-DMHLA-DOClass II Transactivator (CIITA)

Modulation of antigen presentation through competitive peptide binding to the MHC II groove, inhibition of MHC II expression via CIITA modulation, or blockade of peptide loading by inhibiting processing enzymes like Cathepsin S or chaperones like HLA-DM (PubMed, PMID: 22407918).