Inosine Monophosphate Dehydrogenase (IMPDH) Inhibition in Vitro Suppresses Lymphocyte Proliferation and the Production of Immunoglobulins, Autoantibodies and Cytokines in Splenocytes from MRLlpr/lpr Mice

The aim of this study was to evaluate the effects of the immunomodulating drug mycophenolic acid (MPA) on splenocytes in an animal model of systemic lupus erythematosus (SLE), using MRLlpr/lpr mice. MPA reversibly inhibits inosine 5'-monophosphate dehydrogenase, an enzyme involved in the de novo guanosine synthesis. Splenocytes were treated with MPA (at 1 or 10 microM), and stimulated with either lipopolysaccharide (LPS; 10 microg/ml) or concanavalin A (ConA; 1.25 microg/ml). In blocking experiments, guanosine (100 microM) was added to the cultures to inhibit the effects of MPA. Lymphocyte proliferation, enumeration of immunoglobulin producing cells (using ELISPOT) and quantification of anti-double-stranded (ds) DNA antibodies, IFN-gamma and IL-10 (by ELISA) in supernatants were performed. In addition, cell viability was evaluated using propidium iodide and flow cytometry. We found that MPA-treated splenocytes had dramatically decreased mitogen-induced proliferation and number of immunoglobulin producing cells, down-regulated production of IFN-gamma, IL-10 and IgM anti-dsDNA antibodies. The viability of MPA-treated cells was also decreased. All of the effect modulated by MPA could be neutralized by the addition of guanosine. We conclude that MPA has potent immunomodulating effects on both B and T lymphocytes, modulating not only proliferation, but also the production of cytokines, immunoglobulins and autoantibodies.