Cyclosporin A has differential effects on the responses of murine B cells to TI antigens and B-cell mitogens.

The effect of cyclosporin A (CyA) on the response of murine splenocytes to B-cell mitogens, TI-1 and TI-2 antigens was investigated. The proliferative response to LPS was found to be four- to five-fold less sensitive to inhibition than that to dextran sulphate. Antibody responses to a TI-2 antigen in vivo were suppressed by CyA treatment, whereas responses to the TI-1 antigen DNP-LPS were markedly enhanced. Enhanced antibody responses to DNP-LPS were also demonstrable in vitro in the presence of CyA, and the enhancement was not removed by T-cell depletion. LPS-induced antibody production in vitro was enhanced at the same CyA concentrations that inhibited proliferation by 40-50%. The implications of these findings for the mechanism of action of CyA and for our understanding of B-cell differentiation are discussed.