Diagnosis: Histocompatibility: HLA Molecules
• Human leukocyte antigens (HLAs) are the most polymorphic genes in the human genome.
• HLA genes are co-dominantly expressed in each individual.
• HLA proteins bind peptides derived from self and foreign protein antigens. HLA–peptide complexes are exposed on the cell surface of antigen presenting cells (APCs) and interact with the T-cell receptor of cytotoxic or helper T cells.
• HLA class I proteins bind 9– to 12–amino acid long peptides from mostly intracellular proteins and interact with the T-cell receptor of CD8+ cytotoxic T cells.
• HLA class II proteins bind 12– to 16–amino acid long peptides from mostly extracellular and membrane proteins and interact with the T-cell receptor of CD4+ helper T cells.
• Recognition of foreign peptides presented in the context of self-HLA results in activation of T cells.
