Human Class II antigens refer to a group of cell surface proteins that belong to the major histocompatibility complex (MHC) class II family. These antigens play a crucial role in the adaptive immune system by presenting foreign substances, such as peptides derived from pathogens, to immune cells known as T lymphocytes.
The Class II antigens are primarily expressed on the surface of antigen-presenting cells (APCs), including macrophages, dendritic cells, and B cells. They are mainly involved in recognizing and presenting exogenous antigens to CD4+ T cells, initiating a specific immune response against foreign invaders.
The Human Class II antigens are encoded by a set of genes located on chromosome 6 in the human leukocyte antigen (HLA) region. The HLA genes are highly polymorphic, meaning they have multiple alleles that vary between individuals, resulting in diverse antigen presentation capabilities.
These antigens consist of an alpha and a beta chain, which are each encoded by separate genes. The alpha chain forms the antigen-binding groove, while the beta chain contributes to the stability of the complex. These two chains combine to form a heterodimer, which then associates with a peptide derived from an exogenous antigen.
The recognition of antigens by Human Class II molecules facilitates the activation of CD4+ T cells, triggering a cascade of immune responses that aim to eliminate the source of the antigen. This process is essential for the coordinated and precise functioning of the immune system to protect the body against pathogens.
