Class II genes, also known as Major Histocompatibility Complex (MHC) class II genes, are a group of genes that encode cell surface proteins involved in the immune response system in vertebrates. These genes are responsible for presenting antigens – foreign substances that induce an immune response – to immune cells called T lymphocytes.
Class II genes are found in a region of the MHC on human chromosome 6, and similar regions in other vertebrates. They are typically expressed on specialized antigen-presenting cells, such as dendritic cells, macrophages, and B lymphocytes.
The proteins encoded by class II genes are called MHC class II molecules or human leukocyte antigens (HLA) in humans. They are composed of two different chains, alpha and beta, which come together to form a functional complex. These proteins have a binding groove that can accommodate short fragments of antigens, which are typically peptides derived from proteins that have been processed within the antigen-presenting cell.
When these antigens are presented by class II MHC molecules, T lymphocytes recognize them through their specific T cell receptors. This recognition is crucial for activating the adaptive immune response, stimulating the production of antibodies by B cells, or orchestrating the killing of infected or cancerous cells by cytotoxic T lymphocytes.
The diversity of class II genes is important for the recognition of a wide range of antigens and is also responsible for genetic variability in individuals, impacting their susceptibility to various diseases, autoimmunity, and transplantation outcomes.
