Regulation of the antibody response to pneumococcal polysaccharide by thymus-derived cells.

The dose-response relationships in mice immunized with capsular polysaccharide of type 3 Streptococcus pneumoniae (SSS-III) show a distinctive pattern characterized by a single optimal dose for immunization within a relatively narrow range of immunizing doses. Most of the antibody produced is of the IgM class, and the kinetics for the development of both the cellular and serum antibody response to this antigen are parallel up to the peak of the immune response. Although thymus-derived (T) cells are not needed to initiate an antibody response to SSS-III, the magnitude of the antibody response is influenced greatly by the activities of two types of T cells with opposing functions; such regulatory T cells have been termed suppressor and amplifier T cells. The mode of action of suppressor and amplifier T cells as well as the manner in which they might interact during the antibody response to SSS-III are discussed.