DIFFERENT MITOGENIC ACTIVITY OF SOLUBLE AND INSOLUBLE STAPHYLOCOCCAL PROTEIN-A (SPA)

Abstract

The response to SPA and Staphylococcus strain Cowan I (StaCw) of highly purified populations of peripheral blood and tonsil human lymphocytes was investigated. Purified T [thymus-derived] lymphocytes isolated from peripheral blood by E[erythrocyte]-rosetting were unable to respond in vitro to StaCw and showed a poorly significant response to soluble SPA. B[bone marrow-derived]-cell-enriched suspensions of peripheral blood or tonsil responded well to StaCw. EA-RFC [E-antibody rosette forming cell] or EA-RFC-depleted suspensions showed a significant response to soluble SPA, but only EA-RFC-depleted suspensions were activated by StaCw. Highly purified B cell populations from tonsils did not show any proliferative response in the presence of soluble SPA. The addition to highly purified B cell suspensions from human tonsils of increasing concentrations of autologous T lymphocytes did not induce any increase of thymidine uptake in the presence of StaCw. However, it was able to restore a marked proliferative response of the B cell cultures to soluble SPA when mitomycin-treated T lymphocytes were added. The low response of highly purified peripheral blood T lymphocytes to soluble SPA was potentiated by the addition of autologous mitomycin-treated B cells. The unresponsiveness of purified T lymphocytes to StaCw was not affected. Mitogenic activity of SPA coupled to Sepharose beads was different from that of soluble SPA and paralleled that of StaCw. Insoluble SPA probably is a T cell-independent B cell mitogen in man, whereas soluble SPA, like PWM [pokeweed mitogen], exerts its activity on B cells only in the presence of T cells.