Antibody to bacteriophage phi X 174 synthesized by cultured human peripheral blood lymphocytes

Following immunization of human subjects with the antigen bacteriophage phi X 174, concomitant with the rise in serum antibody, cells appear in the circulation which in vitro, without antigen stimulation, synthesize antibody of the same class as serum antibody in most subjects studied. This function is inhibited by puromycin or irradiation, is independent of T cells and occurs within the first 36-72 h of culture. Such cells are found only in recently immunized subjects. Peripheral blood mononuclear cells (PBM) from all immunized subjects synthesize more antibody to phi X 174 in vitro if antigen is present during cell culture; none was synthesized by antigen containing PBM cultures from unimmunized subjects. This antigen-induced antibody response is T cell and antigen dose-dependent and inhibited by puromycin or irradiation. Following primary immunization the antibody synthesized in vivo and in vitro is IgM. Following secondary immunization IgG antibody is immediately detected in vivo but in vitro antigen-induced antibody continues to be IgM for at least 3 months. IgG antibody then appears: once this class switch occurs, in vitro antigen-induced IgG antibody can be demonstrated in cultured PBM of subjects for many years, without further booster immunization.