title: Regulation of B cell function by the immunosuppressive agent leflunomide.
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.
authors.affiliation: Department of Immunology/Microbiology, Section of Rheumatology, Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60612, USA.
authors.forename: K F
authors.initials: KF
authors.lastname: Siemasko
authors.forename: A S
authors.initials: AS
authors.lastname: Chong
authors.forename: J W
authors.initials: JW
authors.lastname: Williams
authors.forename: E G
authors.initials: EG
authors.lastname: Bremer
authors.forename: A
authors.initials: A
authors.lastname: Finnegan
mesh_terms: D000818:Animals; D000917:Antibody Formation / Q000187:drug effects; D001402:B-Lymphocytes / Q000187:drug effects* / Q000502:physiology*; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007555:Isoxazoles / Q000494:pharmacology*; D000077339:Leflunomide; D008070:Lipopolysaccharides / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000187:drug effects; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D013268:Stimulation, Chemical; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D013997:Time Factors
chemical_list: D007166:Immunosuppressive Agents; D007555:Isoxazoles; D008070:Lipopolysaccharides; D000077339:Leflunomide