HLA-B is a gene that provides instructions for making a protein involved in the immune system. This protein is part of the human leukocyte antigen (HLA) complex, which helps the body recognize and respond to foreign substances, such as viruses and bacteria. HLA-B specifically presents pieces of these foreign substances on the surface of cells, allowing immune cells to identify and attack them. Variations in the HLA-B gene can influence an individual's susceptibility to certain diseases, including autoimmune disorders and infections. Additionally, HLA-B typing is important in organ transplantation, as matching donor and recipient HLA types can reduce the risk of transplant rejection.