The Immune Response to Infection

Publisher Summary These various immune responses of a host cell can be divided into antibody and the cell-mediated component. Pre-existing antigen-sensitive B lymphocytes encounter antigen via the immunoglobulin receptor. The antigen is internalized and processed via the exogenous pathway and presented in association with MHC class II molecules to activated T-helper cells. Each T or B cell is committed to respond to a particular epitope. The initial encounter with this epitope, whether in lymphoid tissues or elsewhere in the body, is a small-scale microscopical event. The purpose of the response, especially when the antigen is from an infecting microorganism, is to turn this microscopical event into a larger event as soon as possible, so that both antibody and T cells can be brought into action on a significant scale. Immune reactions are specifically triggered by T and B cells by virtue of their ability to recognize antigen in a highly specific manner. Macrophages and the dendritic cell family, by processing and presenting antigens, exercise a controlling influence at this stage, and are in close physical association with T and B cells. Macrophages, polymorphs, natural killer cells, and complement play an important part as effectors and amplifiers of the reaction in tissues.