REGULATION OF B CELL FUNCTION BY THE IMMUNOSUPPRESSIVE AGENT LEFLUNOMIDE1


    loading  Checking for direct PDF access through Ovid

Abstract

Leflunomide is an immunosuppressive drug capable of inhibiting cellular and humoral mediated responses in vivo. The mechanism responsible for suppression of B cell antibody responses in vivo has not been identified. In this study we demonstrate that leflunomide functions to inhibit murine B cell antibody production by directly acting on the B cell. Experiments performed in vivo showed that both T cell-dependent as well as T cell-independent antigen responses were suppressed by leflunomide. Initial in vitro experiments demonstrated that leflunomide inhibited B cell antibody production by decreasing B cell proliferation. The suppression of B cell proliferation induced by a variety of stimuli that use different signal cascade components suggested that leflunomide was acting on a common component required for B cell proliferation. Kinetic studies with LPS activated B cells revealed that leflunomide retained its inhibitory activity when added as late as 24 hr after stimulation in an 88-hr assay. By analyzing the cell cycle of LPS-stimulated B cells we observed that leflunomide targets two different stages in cell cycle transition: (1) from G1 to S phase and (2) from S phase to G2/M phase. Analysis of one of the cyclin-dependent kinases, Cdk2 protein, by Western blot revealed that Cdk2 levels were decreased, in the presence of leflunomide, 48 hr after stimulation. These data further confirmed that leflunomide inhibited B cell progression through the S phase. We also present evidence that the addition of exogenous uridine reversed the antiproliferative activity of leflunomide. This indicated that leflunomide acted as a pyrimidine synthesis inhibitor, thereby inhibiting B cell proliferation and cell cycle progression.

    loading  Loading Related Articles