Immunological properties of Fc receptor on lymphocytes. 5. Suppressive regulation of humoral immune response by Fc receptor bearing B lymphocytes.

High anti-DNP PFC responses to DNP-DE or DNP-KLH were obtained by transferring normal or primed FcR^? B cell fractions into irradiated syngeneic recipients. On the other hand, the FcR⁺ B cell fraction showed a low precursor activity. Trypsinization of the FcR⁺ B cells, to eliminate remaining antigen-antibody complexes on the surface, failed to augment the response in comparison with that of trypsin-untreated FcR⁺ B cells. Therefore, the weak precursor activity of FcR⁺ B cells seemed to be inherent. No synergistic interaction between the FcR⁺ B and precursor FcR^? B cells, to give rise to the maximum PFC response, was observed. On the contrary, the FcR⁺ B cells significantly suppressed the PFC responses of FcR^? B cells. This kind of suppression could be mediated by a factor released from the FcR⁺ B cell, but not from the FcR^? B or original-unrosetted spleen cell fraction. The factor was not attributable to macrophages, because the FcR⁺ B cells isolated from normal spleen cells, of which macrophages were depleted by Sephadex G-10 columns, could produce the factor with the same activity. Stimulation by specific antigen is not necessary for the induction of the factor(s) as well as of the suppressing FcR⁺ B cells. It seems to be necessary to stimulate FcR by antigen-antibody complexes to produce or release this factor.