Cytotoxic and immunologic effects of methotrexate in psoriasis

Based on recent experience that Cyclosporin A, an immunosuppressive drug, produces marked improvement in psoriasis, possible immunomodulatory activities of methotrexate (MTX) have been reviewed to look for alternate mechanisms of MTX action in psoriasis. It is generally considered that the therapeutic results of MTX in psoriasis are related to a direct effect on epidermal cell hyperplasia through inhibition of DNA synthesis. Several studies in the literature now suggest possible effects of MTX on the immune system of psoriatics as well as in animal models that may have some pathogenic similarities to psoriasis. In psoriatics receiving MTX, neutrophil chemotaxis is suppressed, resulting in a possible alteration in the potential pathologic activity of neutrophils commonly found in lesional skin. MTX does improve both psoriatic and rheumatoid arthritis. Animal studies of the latter using adjuvant arthritis and graft vs host disease (GVHD) have indicated several possible mechanisms for MTX that affect these processes. In GVHD, MTX selectively destroys cycling CD8+ cells, and in adjuvant arthritis the activation of macrophages is prevented by inhibition of T-cell function. While MTX generally has not been clinically utilized as an immunomodulatory drug for immunologically related diseases, it may, nonetheless, have selective actions that could be specific for some diseases. MTX and Cyclosporin A could work mechanistically in similar ways but at different steps in the activation of T cells and macrophages. It may be that the major direct effect of MTX on epidermal cell proliferation is complemented or even mediated by subtle immunoregulatory effects on the melange of cells in the affected skin and the systemic immune response.