Cyclosporin A blocks surface IgM‐mediated growth inhibition in an immature B lymphoma, BKS‐2

Cyclosporin A (CSA) is an immunosuppressive drug, which blocks selective activation pathways in T and B cells. Antigen receptor‐mediated signaling events have been shown to be very sensitive to CSA. Signaling through the surface IgM receptor had been shown to induce growth inhibition in immature B cell lymphoma cells. In this report, we demonstrate that CSA caused significant reversal of growth inhibition induced by an anti‐μ antibody in an immature B lymphoma, BKS‐2. Time‐course experiments indicated that CSA was completely effective when added as late as 4 h after the addition of ligand. CSA was also found to have no direct effect on anti‐μ‐induced Ca²⁺ elevation. These results suggest that the likely target for CSA lies downstream from the initial generation of second messengers, such as Ca²⁺.