The Concept of Antigen Processing and Presentation

THE IMMUNE RESPONSE to protein antigens operates through lymphocytes (the T cells) that recognize products of digestion of the protein antigens. It took years of efforts by many investigators studying different aspects of immunity to reach this conclusion. The initial thinking was that the immune response was directed to antigen not altered by normal catabolism. This holds true for responses of B cells but is definitely not the case for T cells. The CD4 T cells are the essential regulatory cells that influence the function of most leukocytes. Their antigen-specific receptors recognize only protein catabolites that are bound to histocompatibility molecules. Through our initial studies on macrophage biology, consisting of a rather simple series of in vivo experiments, it became apparent that feeding protein antigens to macrophages resulted in a consistent and marked improvement in the immune response to the protein. In other words, the lymphocytes.