Objective: To investigate the roles of tumor necrosis factor alpha(TNFalpha) and the CD40-CD154 interaction in interleukin-12 (IL-12) production by rheumatoid synovial cells (SC).
Methods: Levels of IL-12 (p40 and p70) in synovial tissue and culture supernatants of SC from patients with rheumatoid arthritis (RA), osteoarthritis (OA), and ankylosing spondylitis (AS) were assayed by enzyme-linked immunosorbent assay. Effects of anti-CD154 and anti-TNFalpha antibody on spontaneous and lipopolysaccharide (LPS)-stimulated IL-12 production by SC were examined. Effects of immobilized anti-CD3 treatment and depletion of CD4+ T cells on IL-12 production were also tested. CD154 expression by synovial T cells and intracellular IL-12 production during culture were analyzed by flow cytometry.
Results: IL-12 p40 and p70 levels in RA synovial tissue and spontaneous IL-12 p40 production by SC from RA patients were significantly higher than the levels in OA and AS patients. Spontaneous IL-12 production by SC from RA patients significantly decreased after depletion of CD4+ T cells from SC or after application of anti-CD154 antibody, but not by treatment with anti-TNFalpha antibody. Anti-CD3 antibody stimulation increased spontaneous IL-12 p40 production and CD154 expression by synovial T cells. The increment of IL-12 p40 production by anti-CD3 was abrogated by anti-CD154 antibody. IL-12 p40 production was also increased by LPS stimulation. LPS-stimulated IL-12 production was inhibited by anti-TNFalpha antibody, but not by T cell depletion and anti-CD154 antibody treatment. The TNFalpha inhibitor rolipram inhibited LPS-stimulated IL-12 p40 production by RA SC more strongly than spontaneous production. TNFalpha restored LPS-stimulated IL-12 production that had been inhibited by rolipram.
Conclusion: IL-12 production in RA is regulated by 2 different pathways. One pathway is T cell dependent, predominantly through a CD40-CD154 interaction, while the other is T cell independent, mediated through TNFalpha. Inhibition of IL-12 production by interference with CD40-CD154 interaction and TNFalpha production may be a potential therapeutic strategy for treating RA.