MHC, or major histocompatibility complex, is a group of genes that play a crucial role in the immune system and is present in most vertebrates, including humans. The MHC genes encode cell surface proteins that are essential for the recognition and presentation of antigenic peptides to the immune system. These proteins are critical for distinguishing "self" from "non-self" molecules and initiating an appropriate immune response.
MHC proteins are divided into two classes: class I and class II. Class I MHC molecules are found on almost all nucleated cells and present peptides derived from within the cell to cytotoxic T cells. This recognition helps to ensure that infected or abnormal cells are targeted for destruction. On the other hand, class II MHC molecules are primarily found on antigen-presenting cells, such as macrophages, dendritic cells, and B cells. They present peptides from engulfed foreign substances to helper T cells, which orchestrate a specific immune response against the invader.
The diversity of MHC genes within a population is extensive, with numerous alleles existing for each class I and class II gene. This genetic polymorphism allows for an extensive array of antigen presentation and immune responses, enhancing the ability of a population to combat a wide range of pathogens. MHC molecules also play a critical role in organ transplantation, as they contribute to graft rejection or acceptance by influencing the recognition of transplanted tissues as either self or non-self.
In summary, MHC is a vital component of the immune system, involved in antigen presentation, immune response, and the recognition of self versus non-self molecules.
