ABSTRACT
The major histocompatibility complex (MHC) encodes a large number of molecules which are key participants in the function of the immune system. Included in the human MHC, known as human leukocyte antigen (HLA), are two classes of HLA molecules which are highly polymorphic, and which provide genetic restriction for T lymphocyte responses: HLA class I and HLA class II. Several of the HLA class II molecules are highly associated with, and likely to have a major role in, susceptibility to autoimmune diseases. However, the molecular mechanisms involved are still unclear. In this chapter we address the structure of the HLA molecules and the mechanisms for presenting antigens to the immune system, as well as the correlation of specific HLA alleles with autoimmune diseases.
