[Effect of methotrexate on the immune response in selected experimental models].

Methotrexate (MTX) is one of the immunosuppressory compounds applied in the prophylaxis and treatment of several diseases, including: rheumatoid arthritis, systemic lupus erythematosus, psoriasis, graft-versus-host disease and, in combination with other drugs, neoplastic diseases. Studies in humans and in animal model, of clinical disease, have demonstrated that MTX diminishes the clinical symptoms of various immunological disorders. MTX, an antagonist of folic acid synthesis, causes apoptosis in activated cells, primarily in the G1 and S phases of the cell cycle. One of its actions, is inhibition of the synthesis or activity of several proinflammatory cytokines. At high doses, MTX is cytotoxic to hemopoietic cells; low doses, however, promote hemopoiesis. MTX also induces the differentiation of monocytic tumor cells, which may explain, in part, its therapeutic effects in the treatment of some disorders. The compound suppresses both cellular and humoral immune response and mitogen-induced lymphocyte proliferation. These effects are dose- and time-dependent. The strongest suppressory activity is exerted when MTX is applied 24 or 48 hours after immunization or mitogen stimulation. Administration of MTX in unfavorable conditions such as stress or other diseases, diminishes its tolerance and increases its toxicity. Side-effects of MTX may be ameliorated by application of pharmacological synthetic agents and plant extracts. In summary, MTX has been an effective agent in suppressing immunological disorders (for 50 years) and is still finding many applications.