Class II antigens, also known as major histocompatibility complex (MHC) class II antigens, are cell surface proteins found on a specific group of immune cells called antigen-presenting cells (APCs). These proteins are essential for the immune system to recognize and respond to foreign invaders and play a crucial role in the adaptive immune response.
Class II antigens are constitutively expressed on professional APCs, such as dendritic cells, macrophages, and B-cells. They are responsible for capturing, processing, and presenting antigens to helper T-cells, a type of immune cell that plays a key role in coordinating and directing immune responses.
The primary function of class II antigens is their role in antigen presentation. They bind to specific fragments, or peptides, of foreign antigens that have been engulfed by APCs. These antigen-peptide complexes are then presented on the cell surface, where they can be recognized and bound by specific T-cell receptors on helper T-cells. This interaction triggers the activation of the immune response against the presented antigen.
Class II antigens are highly polymorphic, meaning that they exist in various forms with different genetic variations in different individuals. This polymorphism allows for a broad range of antigens to be presented to the immune system, enhancing the ability to recognize and respond to different pathogens.
In summary, class II antigens are cell surface proteins found on antigen-presenting cells that are essential for capturing, processing, and presenting foreign antigens to helper T-cells. They play a central role in initiating an effective immune response against pathogens.
