We investigated the effect of the
anti-rheumatic drug methotrexate (MTX) on Th1 and Th2 immune responses in mice. For this investigation, mice were immunized subcutaneously at the base of the tail with
ovalbumin (OVA) emulsified with complete
Freund's adjuvant (day 0). Varying doses of MTX were orally administered daily from days 0 to 20. On day 21, anti-OVA
IgG2a and
interferon-gamma (IFN-gamma) as indicators of Th1 responses and anti-OVA
IgG1 and
interleukin-10 (IL-10) as those of Th2 responses were measured. The results showed that treatment with MTX was followed by decreases in OVA-specific
IgG and proliferation of spleen cells to the
antigen. The
anti-rheumatic drug inhibited both anti-OVA
IgG2a and
IgG1 production, although the inhibitory effect of MTX on the
antigen-specific
IgG2a production appeared to be greater than that on
IgG1 production. IFN-gamma, but not
IL-10, secretion was markedly downregulated by MTX. Administration of MTX resulted in suppression of
antigen (OVA)-induced
arthritis in mice. The suppression of the joint
inflammation by MTX was associated with inhibition of OVA-specific proliferative responses of spleen cells, anti-OVA
IgG,
IgG2a and
IgG1 production, and IFN-gamma and
IL-10 secretion, although more pronounced decreases in
IgG2a and IFN-gamma were observed compared with those in
IgG1 and
IL-10 in MTX-treated mice. These results indicate that MTX appears to suppress Th1 and, to a lesser extent, Th2 immune responses and its anti-arthritic effect on human
rheumatoid arthritis might be at least in part explained by down-regulation of Th1 responses involved in the disease.