HLA - A,B,C,DR Typing

HLA‑A, HLA‑B and HLA‑C are genes encoding MHC class I proteins expressed on almost all nucleated cells. They present intracellular peptide fragments to CD8+ T lymphocytes, enabling detection of infected or abnormal cells. These loci are highly polymorphic and are crucial for immune responses, organ-transplant compatibility, and associations with certain autoimmune diseases and drug hypersensitivities.

HLA typing identifies which human leukocyte antigen (HLA) genes and proteins a person carries. It’s used primarily to match organ, tissue and bone marrow donors with recipients to reduce rejection risk, and to predict susceptibility to certain autoimmune conditions and hypersensitivity to specific drugs. Results guide transplant decisions, donor selection and, sometimes, diagnosis or risk assessment for immune-related disorders.

HLA‑B27 typing is a blood test that detects the HLA‑B27 gene variant, a genetic marker linked to higher risk of certain inflammatory joint conditions (for example ankylosing spondylitis, reactive arthritis, some psoriatic and inflammatory bowel disease–related arthritis). A positive result raises suspicion but isn’t diagnostic—clinical assessment and imaging are needed. Many people with HLA‑B27 never develop disease.

HLA-DR and HLA-DQ are human leukocyte antigen (HLA) class II proteins on antigen-presenting cells that present peptide fragments to CD4+ T lymphocytes. Encoded within the HLA complex on chromosome 6, different HLA-DR and -DQ alleles influence immune responses, susceptibility to autoimmune diseases (e.g., type 1 diabetes, celiac disease) and compatibility in organ transplantation and transfusion.

HLA-DR stands for human leukocyte antigen DR, a class II major histocompatibility complex molecule. It is expressed on antigen-presenting cells (dendritic cells, B cells, macrophages) and presents peptide fragments to CD4+ T lymphocytes, initiating immune responses. HLA-DR typing is used for transplant compatibility and is linked to susceptibility to certain autoimmune diseases via specific allele variants.

HLA‑B testing identifies specific variants (alleles) of the HLA‑B gene, part of the HLA class I system. It’s used to detect genetic predisposition to conditions like ankylosing spondylitis and other spondyloarthropathies, to predict drug hypersensitivity (eg, abacavir and certain antiepileptics), and to help match donors and recipients for organ or stem‑cell transplantation.