Human leukocyte antigen class I and II molecules (HLA class I and II)

Human leukocyte antigen (HLA) class I and II molecules are a group of highly polymorphic glycoproteins encoded by the Major Histocompatibility Complex (MHC) on chromosome 6 (Source: StatPearls, 2023). HLA class I molecules (HLA-A, -B, -C) are expressed on all nucleated cells and present endogenous peptides to CD8+ cytotoxic T cells, while HLA class II molecules (HLA-DR, -DQ, -DP) are primarily found on professional antigen-presenting cells like dendritic cells and B cells, presenting exogenous peptides to CD4+ helper T cells (Source: Janeway's Immunobiology, 9th Ed). Their fundamental role is to distinguish 'self' from 'non-self,' facilitating the elimination of infected or malignant cells while maintaining immune tolerance (Source: Nature Reviews Immunology, 2018). In clinical practice, HLA molecules are major determinants of transplant compatibility, where mismatches trigger T-cell mediated rejection or graft-versus-host disease (Source: NIH/MedlinePlus, 2022). Furthermore, specific HLA alleles are linked to severe drug hypersensitivity reactions, such as HLA-B*57:01 and abacavir-induced hypersensitivity, where the drug binds directly to the HLA groove to alter the repertoire of presented peptides (Source: FDA Labeling, 2021). HLA expression is also a key factor in the efficacy of modern immunotherapies, including checkpoint inhibitors and TCR-engineered T-cell therapies, which rely on the presentation of tumor-associated antigens (Source: PubMed/Journal of Clinical Investigation, 2020).

Other names

Major Histocompatibility Complex class I and IIMHC class I and IIHLA-I and HLA-IIHuman MHCHLA-A, -B, -C, -DR, -DQ, -DP

Presentation of antigenic peptides to T-cell receptors (TCR) to initiate or modulate immune responses; certain drugs bind directly to the HLA peptide-binding groove to alter peptide specificity (Source: Nature, 2012).