Regulation of B cell function by the immunosuppressive agent leflunomide

Transplantation. 1996 Feb 27;61(4):635-42. doi: 10.1097/00007890-199602270-00020.


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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antibody Formation / drug effects
  • B-Lymphocytes / drug effects*
  • B-Lymphocytes / physiology*
  • Cell Cycle / drug effects
  • Cell Division / drug effects
  • Immunosuppressive Agents / pharmacology*
  • Isoxazoles / pharmacology*
  • Leflunomide
  • Lipopolysaccharides / pharmacology
  • Lymphocyte Activation / drug effects
  • Male
  • Mice
  • Mice, Inbred Strains
  • Stimulation, Chemical
  • T-Lymphocytes / drug effects
  • T-Lymphocytes / immunology
  • Time Factors


  • Immunosuppressive Agents
  • Isoxazoles
  • Lipopolysaccharides
  • Leflunomide