Effects of methotrexate on differentiation of monocytes and production of cytokine inhibitors by monocytes.

OBJECTIVE

To examine the potential of methotrexate (MTX) to act as a differentiation-stimulating factor for monocytes, which could explain the antiinflammatory properties of this agent in the treatment of rheumatoid arthritis (RA).

METHODS

Fluorescence-activated cell sorter analysis was used to measure the changes in antigen expression (CD11b/c, CD16, CD64, CD14, CD68, and CD95) in response to MTX, 1,25-OH-cholecalciferol (1,25-OH-CCF), and granulocyte-macrophage colony-stimulating factor in the human monoblastic leukemia cell line U937, bone marrow mononuclear cells (BMMC), and peripheral blood mononuclear cells (PBMC). Release of interleukin-1beta (IL-1beta), IL-1 receptor antagonist (IL-1Ra), tumor necrosis factor a, and soluble tumor necrosis factor receptors (sTNFR) p55 and p75 during the differentiation in vitro was assessed by immunoassay in the culture supernatants.

RESULTS

MTX alone and in combination with 1,25-OH-CCF markedly stimulated the differentiation of the monocytic U937 cells and simultaneously increased Fas-antigen expression. Differentiation was associated with enhanced IL-1Ra and sTNFR p75 release from U937 cells. MTX had fewer effects on phenotypic differentiation of human BMMC and PBMC, but did stimulate IL-1Ra release and inhibit IL-1beta synthesis in BMMC.

CONCLUSION

MTX acts as a strong differentiation factor for immature and undifferentiated monocytic cells. Differentiation in vitro is associated with an increase in natural cytokine inhibitor release and a simultaneous down-regulation of IL-1beta. These findings may explain the marked clinical antiinflammatory effects of MTX when used in the treatment of RA.