Objective: Prostaglandin E2 (PGE2) has a wide range of regulatory action in diverse cell types. To investigate the role of PGE2 in rheumatoid arthritis (RA), we tested the effect of exogenous PGE2 on the production of cytokines in synoviocytes.
Methods: Fibroblast-like synoviocytes (FLS) were prepared from the synovial tissue of patients with RA and cultured in the presence of PGE2. The production of interleukin 15 (IL-15) and IL-10 were measured in culture supernatant by ELISA. IL-15 mRNA expression and nuclear factor-kappaB binding activity for IL- 15 transcription were determined by reverse transcription-polymerase chain reaction and electrophoresis mobility shift assay (EMSA), respectively. The level of IL-15 production was also measured by Western blot.
Results: PGE2 at concentrations from 10(-11) to 10(-5) M inhibited secretion of IL-15 by FLS, while increasing IL-10 production, in a dose dependent manner. IL-15 production stimulated by interferon-gamma (IFN-gamma), IL-1beta, or lipopolysaccharide were also strongly inhibited by PGE2. This PGE2-mediated inhibition of IL-15 production appears to be dependent in part on the increase of IL-10, since neutralizing anti-IL-10 antibodies reversed this inhibition to some extent. The EMSA of the NF-kappaB site in the IL-15 promoter showed that PGE2 inhibited binding of NF-kappaB in a dose dependent manner. Experiments using inducers and an inhibitor of cyclic AMP (cAMP) suggest that a major intracellular signal mediates the regulatory effect of PGE2 on the production of IL-15 and IL-10.
Conclusion: PGE2 differentially regulates the production of IL-15 and IL-10 in FLS. The strong inhibition of PGE2 on IL-15 production is exerted via a cAMP-dependent modulation of NF-kappaB activity. Our data suggest that overproduced PGE2 in RA joints may play an antiinflammatory role.