Antiproliferative effects of methotrexate on peripheral blood mononuclear cells

Methotrexate was added to cultured mononuclear cells from the peripheral blood of normal individuals and patients with rheumatoid arthritis (RA) to study the drug's effects on mononuclear cell proliferation and antibody synthesis. In the presence of methotrexate, marked antiproliferative effects (to levels less than 15% of baseline) were seen with 3H-deoxyuridine, but not with 3H-thymidine, as the marker of cell division. This difference was not due to altered kinetics of proliferation or the presence of salvage nucleotides in the culture medium. The absence of suppression of antibody production preactivated by pokeweed mitogen in vitro and the low levels of suppression of spontaneous IgM rheumatoid factor production by blood mononuclear cells from RA patients suggested a relative resistance of activated cells to the effects of methotrexate. The effects of methotrexate on both cell proliferation and antibody synthesis were completely reversed by the addition of high concentrations of exogenous folinic acid. The results suggest that methotrexate has effects on immunocompetent cells that may contribute to the efficacy of this drug in the treatment of RA and other autoimmune diseases.