Suppressive effect of interleukin-4 (IL-4) on IL-6 production by adherent rheumatoid synovial cells.

Interleukin-6 (IL-6) has recently been characterized as a mediator of multiple inflammatory responses. Excessive production of this cytokine has been demonstrated in the joints of patients with rheumatoid arthritis (RA). On the other hand, anti-inflammatory effects of IL-4 have recently been demonstrated. We therefore investigated the suppressive effect of IL-4 on IL-6 production by synovial cells in patients with RA. Freshly prepared adherent rheumatoid synovial cells expressed IL-6 mRNA and spontaneously produced a large amount of IL-6 in culture. This spontaneous production of IL-6 was significantly suppressed by IL-4. The suppressive effect of IL-4 on IL-6 production was demonstrated in all patients with RA tested in this study. On the other hand, IL-6 mRNA levels already expressed in adherent synovial cells were not reduced by IL-4 in 24 hr of culture. The suppressive effect of IL-4 on IL-6 production suggests that IL-4 is an important physiological regulator of IL-6 production in synovial cells.