Class II histocompatibility antigens, also known as major histocompatibility complex (MHC) class II antigens, are molecular markers found on the surface of cells that play a crucial role in the immune response. These antigens are primarily involved in the recognition and presentation of foreign substances, such as pathogens or antigens derived from these pathogens, to the immune system.
Class II histocompatibility antigens are encoded by genes within the MHC locus, which is a region on chromosome 6 in humans. They are typically expressed on professional antigen-presenting cells (APCs) such as dendritic cells, macrophages, and B lymphocytes, as well as on some non-professional APCs including fibroblasts and endothelial cells.
Their main function is to capture and present antigenic peptides to CD4+ T lymphocytes, a subset of immune cells involved in cell-mediated immunity. This interaction between the class II antigens and the T lymphocytes is critical for the activation of an immune response, during which T cells recognize the presented peptide as foreign and initiate an immune reaction to eliminate the threat.
In addition to their role as antigen presentation molecules, class II histocompatibility antigens also play a role in immune regulation, as they are involved in the selection and development of T lymphocytes in the thymus.
The study of class II histocompatibility antigens is essential for understanding immune-mediated diseases, organ transplantation, and vaccine development, as they are central to the recognition and elimination of foreign substances by the immune system.
