HLA-As are a family of proteins that are important for cell surface expression of many different types of antigens. Some of the cells that contain HLA-As are those that are responsible for producing many different types of antibodies and the cells responsible for producing antibodies play a key role in immune responses. Antibodies that fight infections can identify a wide range of different invaders because they bind to very different types of molecules on the surfaces of the bacteria and viruses that invade the body. Once antibodies bind to the invader, they can cause the destruction of that virus or bacterium.
People who lack HLA-A and HLA-B have very poor cellular immunity. If you have a defective HLA-A or -B gene, your HLA-A body’s ability to produce enough antibodies is greatly reduced. The problem usually affects the lymph nodes that drain the area of the infection and therefore, patients experience recurrent infections.
Because of the many different types of HLA-As and the variety of their functions, there are many different kinds of genetic defects in the HLA region of the genome. HLA deficiencies are common in certain groups of patients. For example, patients with X-linked agammaglobulinemia lack B cells. They have HLA-A and HLA-B deficiencies.