Enhancing antibody: a novel component of the immune response.

Current descriptions of the immune response identify two classes of antigenic stimuli that result in the production of specific antibody: (i) exogenous antigens and (ii) endogenous variable-region determinants of the immune system. We expand this scheme to include a third class of antigenic stimulus--new determinants created by the binding of antibody to antigen. This paper describes a set of monoclonal antibodies which arose after repeated immunization with antigen alone but which bound antibody--antigen complexes. These antibodies recognize determinants on the antibody portion of the complexes that were expressed as a consequence of antigen binding. Antibodies of this general type, "enhancing antibodies," which can strengthen antibody--antigen and idiotypic-anti-idiotypic antibody interactions, may play important regulatory and effector roles in the immune response. We suggest a model that predicts the occurrence and specificity of different classes of such antibodies and provides a conceptual framework that gives a straightforward explanation of the appearance in the immune response of rheumatoid antibodies and of antibodies that bind cooperatively to antigen.