MHCantigéns

MHCantigéns, often referred to as Major Histocompatibility Complex antigens, are proteins found on the surface of cells in vertebrates. They play a crucial role in the adaptive immune system by presenting peptide fragments to T cells. These peptide fragments can originate from either the body's own proteins or from foreign invaders like bacteria and viruses. The MHC complex is highly polymorphic, meaning there are many different versions of these genes within a population. This genetic diversity is essential for the survival of a species, as it increases the likelihood that at least some individuals will be able to present a wide range of foreign antigens to their immune systems.

There are two main classes of MHC molecules. Class I MHC molecules are found on almost all nucleated cells and present intracellular antigens, such as viral proteins, to cytotoxic T lymphocytes (CTLs). CTLs then recognize and eliminate infected cells. Class II MHC molecules are primarily found on antigen-presenting cells (APCs) like macrophages, dendritic cells, and B cells. They present extracellular antigens, which have been taken up by the APC, to helper T lymphocytes. Helper T cells then orchestrate the immune response by activating other immune cells. The recognition of MHC-peptide complexes by T cells is a fundamental process in distinguishing self from non-self, thereby initiating an appropriate immune response and preventing autoimmune reactions.