Know Your Immunity Genes : HLA

Know Your Immunity Genes: HLA

The Human Leukocyte Antigen (HLA) system is one of the most important — and most complex — components of the human immune system. HLA genes encode proteins that sit on the surface of cells and help the immune system distinguish “self” from “non-self” — identifying and destroying pathogens, cancer cells, and other foreign invaders.

What Is the HLA System?

The HLA system is encoded by a cluster of genes on chromosome 6 called the Major Histocompatibility Complex (MHC). HLA proteins present fragments of proteins (antigens) to T cells, which then mount an immune response. There are two main classes:

• HLA Class I (HLA-A, HLA-B, HLA-C) — present antigens to cytotoxic T cells (CD8+). Found on the surface of almost all nucleated cells

• HLA Class II (HLA-DR, HLA-DQ, HLA-DP) — present antigens to helper T cells (CD4+). Found on the surface of immune cells (dendritic cells, macrophages, B cells)

Why HLA Matters for COVID-19

HLA variants influence how effectively the immune system recognises and responds to SARS-CoV-2. Certain HLA types are associated with stronger immune responses to coronavirus, while others are associated with increased susceptibility to severe disease. HLA typing is also critical for organ transplantation, blood transfusion, and bone marrow donation — mismatched HLA types can trigger rejection.

HLA and Autoimmune Disease

Many autoimmune diseases are strongly associated with specific HLA types. For example, HLA-B27 is associated with ankylosing spondylitis; HLA-DQ2 and HLA-DQ8 are associated with coeliac disease; HLA-DR4 is associated with rheumatoid arthritis. Understanding your HLA type can help identify your risk for these conditions.