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

Human leukocyte antigen (HLA) class I and class II molecules are highly polymorphic glycoproteins encoded by the major histocompatibility complex (MHC) on chromosome 6. HLA class I molecules, composed of a heavy α chain and β2-microglobulin, are expressed on nearly all nucleated cells and primarily present intracellular (endogenous) peptides to CD8+ cytotoxic T cells, enabling immune surveillance of infected or malignant cells[1][4][5][7]. HLA class II molecules, made of α and β chains, are mainly found on antigen-presenting cells (dendritic cells, macrophages, B cells), and present extracellular (exogenous) peptide antigens to CD4+ helper T cells, crucial for initiating the adaptive immune response[1][3][4][7]. Both classes display a peptide-binding groove with specificity for peptide length and sequence, underpinning their diversity and central role in distinguishing self from non-self[1][4][5][7]. HLA molecules are the principal determinants of histocompatibility in transplantation and major genetic factors in autoimmune disease susceptibility, cancer immune escape, infectious disease resistance or vulnerability, and drug hypersensitivity. Therapies targeting or modulating HLA functions are foundational in transplantation medicine, cancer immunotherapy, and the treatment of autoimmunity[1][3][7].

Other names

Major histocompatibility complex class I moleculeMajor histocompatibility complex class II moleculeHLA-I and HLA-II moleculesHLA-A, HLA-B, HLA-C (class I main forms)HLA-DR, HLA-DP, HLA-DQ (class II main forms)MHC class I and MHC class II (general/non-human terminology)

Modulation of peptide antigen presentation; Blocking HLA-T-cell interactions; Modifying T-cell activation through antigen presentation pathways; Disrupting costimulatory signaling necessary for full immune activation; Inducing immune tolerance (in transplantation or autoimmune therapy contexts)