Human leukocyte antigen class I molecule, Human leukocyte antigen class II molecule, and T cell receptor (HLA class I, HLA class II, TCR)

Human leukocyte antigen (HLA) class I and II molecules are cell-surface glycoproteins, encoded by the major histocompatibility complex (MHC), that present peptide antigens to T cell receptors (TCRs) on T lymphocytes[1][6]. HLA class I molecules present endogenously derived peptides (typically 8-10 amino acids) to CD8+ cytotoxic T lymphocytes and are expressed on nearly all nucleated cells, while HLA class II molecules present exogenous peptides (typically longer, >11 amino acids) to CD4+ helper T lymphocytes and are mainly expressed on antigen-presenting cells such as dendritic cells, macrophages, and B cells[1][5][6]. The T cell receptor is a highly variable, disulfide-linked heterodimer (usually alpha/beta), which recognizes the combination of peptide and MHC molecule (peptide/MHC complex), initiating T cell activation and the adaptive immune response[3][2][4][7]. Genetic diversity in HLA alleles underpins individual variation in disease susceptibility, immune responses, and transplant compatibility[1][6]. Dysfunction or therapeutic modulation of these pathways is implicated in cancer, infection, autoimmune disease, and transplant rejection. Because this query combines two target families (HLA molecules and T cell receptors), it describes a multi-molecular immune recognition axis rather than a singular discrete target. Standard practice is to list these molecules individually (e.g., "Human leukocyte antigen class I molecule" or "T cell receptor"); combining them may complicate downstream structured data use.

Other names

HLA-IHLA-IIMajor histocompatibility complex class IMajor histocompatibility complex class IIMHC class IMHC class IITCRT-cell antigen receptor

Blocking antigen presentation to modulate immune response; Inhibiting T cell activation by blocking TCR or associated signaling; Modulating T cell recognition or alloreactivity in transplantation; Inducing immune tolerance (for autoimmune disease settings)