Antigen Presentation System

The antigen presentation system refers to the immune process in which antigens, typically derived from pathogens or abnormal host cells, are processed and displayed on the cell surface by major histocompatibility complex (MHC) molecules. This display enables T lymphocytes, crucial players of adaptive immunity, to recognize and mount a targeted immune response. Professional antigen-presenting cells (APCs) such as dendritic cells, macrophages, and B cells are central to this process, as they process exogenous antigens (via MHC class II) or endogenous antigens (via MHC class I), and provide the necessary costimulatory signals for T cell activation. The efficiency and regulation of this system are critical for defense against pathogens and tumor cells, and for maintaining self-tolerance to avoid autoimmune reactions.

Other names

Antigen presentationAntigen processing and presentationAntigen-presenting pathway

Many immunotherapies work by enhancing or inhibiting antigen presentation, e.g., monoclonal antibodies targeting checkpoint molecules (PD-1, CTLA-4) to promote T cell activation. Adjuvants in vaccines often enhance antigen presentation by stimulating APC maturation.