사용자:Kimhs5400/작업실

Because MHC genes must defend against a great diversity of microbes in the environment, with a great diversity of proteins, the MHC genes themselves must be diverse. The MHC is the most gene-dense region of the mammalian genome. MHC genes vary greatly from individual to individual, that is, MHC alleles have polymorphisms (diversity). This polymorphism is adaptive in evolution because it increases the likelihood that at least some individuals of a population will survive an epidemic.

There are two general classes of MHC molecules: Class I and Class II. Class I MHC molecules are found on almost all cells and present proteins to cytotoxic T cells. Class II MHC molecules are found on certain immune cells themselves, chiefly macrophages and B cells, also known as antigen-presenting cells (APCs). These APCs ingest microbes, destroy them, and digest them into fragments. The Class II MHC molecules on the APCs present the fragments to helper T cells, which stimulate an immune reaction from other cells.