Histocompatibility antigens class II, also known as human leukocyte antigens (HLAs) class II, are a group of proteins present on the surface of cells that play a crucial role in the immune response within vertebrates, particularly humans. These antigens are encoded by the genes of the major histocompatibility complex (MHC) located on chromosome 6 in humans.
Histocompatibility antigens class II proteins are primarily expressed on the surface of antigen-presenting cells (APCs) such as macrophages, dendritic cells, and B cells. Their main function is to present antigens to T cells, a key step in the adaptive immune response. These antigens act as recognition markers, allowing the immune system to distinguish self from non-self molecules or pathogens.
The proteins that make up histocompatibility antigens class II are composed of two subunits known as alpha and beta chains, both of which are essential for proper antigen presentation. The alpha and beta chains are encoded by separate genes within the MHC. Variations in these genes give rise to a wide range of histocompatibility antigens class II alleles, resulting in diverse antigen-binding specificities.
Histocompatibility antigens class II play a crucial role in transplantation medicine, as they determine the compatibility between the tissues of a donor and a recipient. Matching these antigens between donor and recipient is vital to minimize immune rejection and improve the success of organ and tissue transplants.
Overall, histocompatibility antigens class II are integral components of the immune system, ensuring appropriate immune responses and facilitating the recognition and elimination of foreign substances or pathogens.
