HLA- (CLASS II ) TYPING

HLA Class II are cell-surface proteins on professional antigen-presenting cells (dendritic cells, macrophages, B cells) that present peptides derived from extracellular proteins to CD4+ helper T cells. Composed of polymorphic alpha and beta chains encoded by HLA-DR, -DQ and -DP genes, they are essential for adaptive immune activation, vaccine responses, transplant matching and influence autoimmune disease risk.

Class II HLA antigens are polymorphic cell-surface glycoproteins (HLA-DR, -DP, -DQ) expressed mainly on antigen-presenting cells (dendritic cells, macrophages, B cells). They consist of alpha and beta chains and present extracellularly derived peptide fragments to CD4+ helper T cells, initiating adaptive immune responses. Class II molecules are crucial for pathogen defense, immune regulation, transplant compatibility, and autoimmune disease risk.

HLA Type I (HLA-A, -B, -C) are on almost all nucleated cells, present endogenous peptides to CD8+ cytotoxic T cells, and influence natural killer cell activity. HLA Type II (HLA-DR, -DP, -DQ) are on antigen-presenting cells (dendritic cells, macrophages, B cells), present exogenous peptides to CD4+ helper T cells, and drive adaptive immune activation and antibody responses.

HLA class II supertypes are the three main groups: HLA-DR, HLA-DQ, and HLA-DP. These heterodimeric molecules present extracellularly derived peptides to CD4+ T lymphocytes, orchestrating helper T-cell responses and antibody production. Polymorphic alpha and beta chains within each supertype determine peptide-binding specificities and influence individual immune responsiveness.

HLA‑DR2 (serotype covering DRB1*15/*16) is associated with several immune-mediated disorders. Strong links include multiple sclerosis and narcolepsy with cataplexy; other reported associations are systemic lupus erythematosus and Goodpasture’s (anti‑GBM) disease. These associations reflect altered antigen presentation and increased autoimmune susceptibility rather than direct causation; individual risk depends on many genetic and environmental factors.

HLA typing identifies a person’s human leukocyte antigen genes and specific alleles including class I (A, B, C) and class II (DR, DQ, DP). It assesses tissue compatibility for organ and stem‑cell transplantation, helps match donors, evaluates genetic susceptibility to some autoimmune conditions, and predicts certain drug hypersensitivity reactions. Results guide transplant decisions and clinical risk assessment.