Methotrexate specifically modulates cytokine production by T cells and macrophages in murine collagen-induced arthritis (CIA): a mechanism for methotrexate-mediated immunosuppression

Immunosuppressive therapy with methotrexate (MTX) has been established as e ffective treatment for patients with rheumatoid arthritis. To analyse the t herapeutic potential and mechanisms of action of MTX, we determined serum c ytokine levels and cytokine production by splenic T cells and macrophages i n untreated and MTX-treated mice. Furthermore, we assessed the role of MTX in a murine model of experimental arthritis induced by collagen type II (CI A). MTX reduced spontaneous and IL-15-induced tumour necrosis factor (TNF) production by splenic T cells but not by macrophages from healthy mice in v itro in a dose-dependent manner. In contrast, interferon-gamma (IFN-gamma) production was less strikingly reduced and IL-4 production was virtually un affected. In addition, treatment of healthy mice with MTX in vivo led to re duced TNF serum levels and diminished TNF production by splenic T cells and macrophages. Intraperitoneal administration of MTX prior to the onset of a rthritis completely prevented clinical and pathological signs of CIA. This was associated with a striking reduction of TNF production by spleen cells from MTX-treated mice. The role of TNF in MTX-mediated effects on cytokine production was further underlined by the finding that MTX effects on IFN-ga mma production were augmented in TNF-transgenic mice but abrogated in mice in which the TNF-alpha gene had been inactivated by homologous recombinatio n. Thus, MTX specifically modulates spontaneous and IL-15-induced TNF-alpha production in mice and prevents experimental murine CIA. These data sugges t that TNF production by T cells is an important target of MTX and may serv e as a basis to understand and further analyse MTX-mediated mechanisms of i mmunosuppression in patients with RA.