IL-1 beta and IL-6 stimulate the production of platelet-activating factor (PAF) by cultured rabbit synovial cells.

The aim of this study was to determine whether synovial cells are capable of producing PAF in the presence of cytokines such as IL-1 beta and IL-6 and other stimuli. Synovial cells were obtained from joints of healthy rabbits. PAF production was assayed by measurement of serotonin release in rabbit platelets and the incorporation of 3H-acetate into PAF. Synovial cells produced PAF after 5 min of incubation with ionophore A23187, reaching the maximal amount at 15 min (4.3 +/- 0.7 x 10(-3) pmol of PAF/mg protein, P < 0.005, n = 4), and declining afterwards. The treatment of synoviocytes with IL-1 beta and IL-6 induced synthesis of PAF after 5 min of stimulation, reaching the greatest production at 15 min with IL-6 and 30 min with IL-1 beta (3.6 +/- 1.1 x 10(-3) and 3.3 +/- 1.2 pmol of PAF/mg protein, respectively, P < 0.05, n = 4). The incubation of the cells with PMSF, an inhibitor of acetylhydrolase, before the addition of the stimuli, increased the incorporation rate of 3H-acetate, suggesting a rapid degradation of PAF by synoviocytes. These results demonstrate that synovial cells can produce PAF after stimulation with agonists, such as ionophore, and cytokines. Thus, PAF, acting alone or with other mediators, could amplify the inflammatory joint reaction.