title: Strong mitogenic effect for murine B lymphocytes of an immunosuppressor substance released by Streptococcus intermedius.
abstract: A noncytotoxic protein substance, produced by Streptococcus intermedius, with very potent immunosuppressive properties (F3'EP-Si) was tested for lymphocyte mitogenic activity. Although devoid of T-cell mitogenicity, F3'EP-Si stimulated proliferation and led to high numbers of plaque-forming cells in cultures of normal or T-cell-depleted, small or large splenic B cells from both lipopolysaccharide-responding and -nonresponding mice. The B-cell mitogenic activity of F3'EP-Si was quantitatively comparable to that of lipopolysaccharide, and the simultaneous exposure to both mitogens stimulated additive B-cell responses. Injection of F3'EP-Si into normal mice resulted in increased numbers of spleen cells, higher rates of mitotic activity, and very large numbers of plaque-forming cells, predominantly of the immunoglobulin G2a and -b isotypes. In preliminary experiments, the analysis of surface markers among the lymphocytes participating in the blastogenic response in vivo revealed a T-cell component in the response to F3'EP-Si. These observations are discussed in the context of the immunosuppressive activity of this and other microbial substances.
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology*; D001426:Bacterial Proteins / Q000276:immunology*; D004261:DNA Replication; D007165:Immunosuppression Therapy; D007700:Kinetics; D008213:Lymphocyte Activation; D051379:Mice; D008805:Mice, Inbred A; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D013045:Species Specificity; D013291:Streptococcus / Q000276:immunology*
chemical_list: D001426:Bacterial Proteins