HLA-A 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-A specifically presents pieces of these foreign substances on the surface of cells, allowing immune cells to identify and attack them. The HLA complex is crucial for tissue compatibility in organ transplants, as it helps determine whether the immune system will accept or reject a transplanted organ. Variations in the HLA-A gene can influence an individual's susceptibility to certain diseases and their response to treatments.