HLA molecules A, B, and C belong to which MHC class?

HLA molecules A, B, and C belong to which MHC class?

• A. Class I
• B. Class II
• C. Class III
• D. Class IV

Answer: (A)

MHC class I molecules present intracellular peptides to CD8+ T cells. HLA-A, HLA-B, and HLA-C are the classical class I antigens; they are expressed on almost all nucleated cells and form a complex with beta-2 microglobulin. The peptide-binding groove, made by the heavy chain’s alpha-1 and alpha-2 domains, typically binds short peptides (about 8–10 amino acids) derived from proteins inside the cell, such as viral or tumor proteins, enabling CD8+ cytotoxic T cell recognition. This contrasts with MHC class II, which are expressed mainly on professional antigen-presenting cells and present longer exogenous peptides to CD4+ T cells, and with class III, which does not encode MHC molecules but other immune proteins such as some complement components and TNF.

MHC class I molecules present intracellular peptides to CD8+ T cells. HLA-A, HLA-B, and HLA-C are the classical class I antigens; they are expressed on almost all nucleated cells and form a complex with beta-2 microglobulin. The peptide-binding groove, made by the heavy chain’s alpha-1 and alpha-2 domains, typically binds short peptides (about 8–10 amino acids) derived from proteins inside the cell, such as viral or tumor proteins, enabling CD8+ cytotoxic T cell recognition. This contrasts with MHC class II, which are expressed mainly on professional antigen-presenting cells and present longer exogenous peptides to CD4+ T cells, and with class III, which does not encode MHC molecules but other immune proteins such as some complement components and TNF.