Major Histocompatibility Complex Class II Protein (MHC II)

Major histocompatibility complex class II (MHC II) proteins are membrane-bound glycoproteins essential for the adaptive immune response. They present peptide antigens derived from extracellular proteins to CD4+ T lymphocytes, thereby initiating and regulating immune responses against pathogens and foreign antigens. MHC II molecules are heterodimers composed of an α (alpha) chain and a β (beta) chain. They are constitutively expressed on professional antigen-presenting cells (APCs): dendritic cells, macrophages/monocytes, B cells, and also found on thymic epithelial cells. Expression can be induced on other cell types by interferon gamma (IFNγ). MHC class II molecules play a central role in orchestrating adaptive immunity through their unique ability to sample extracellular environments and present processed antigens specifically recognized by helper T lymphocytes—a process fundamental both during infection control and vaccine-induced protection.

Other names

MHC class IIMHC-IIHuman Leukocyte Antigen Class IIHLA Class II