Effects of cyclosporine and rapamycin on immunoglobulin production by preactivated human B cells

In order to assess the direct effects of cyclosporine A (CsA) and rapamycin on B cells, we utilized a two-segment culture system of highly purified B lymphocytes consisting of induction (activation) in the presence of the formalinized Staphylococcus aureus bacteria and IL-2, and differentiation, respectively, in the presence of various combinations of cytokines. Results show that rapamycin strongly inhibited production of both IgM and IgG measured at the end of the secondary culture supported by IL-2/IL-6, whereas CsA up-regulated the immunoglobulin production. The stimulatory effect of CsA was also observed when preactivated B cells were recultured in absence of any cytokines. These results show that rapamycin and CsA have clearly distinct effects on human B lymphocyte responses in vitro. Rapamycin is a more potent in vitro immunosuppressant of B lymphocytes than CsA. It is effective at significantly lower concentrations, and it does not stimulate either the proliferation or antibody production by preactivated B cells.