IL-10 stimulates production of platelet-activating factor by monocytes of patients with active systemic lupus erythematosus (SLE)

IL-10 displays modulatory properties on the synthesis of platelet-activatin g factor (PAF), a potent inflammatory mediator of vascular injury. Despite the fact that IL-10 is considered to be an anti-inflammatory cytokine, IL-1 0 levels correlate with disease activity in SLE. Moreover, in SLE IL-10 is unable to exert its immunosuppressive and anti-inflammatory effects. We hav e investigated the ability of IL-10 to stimulate PAF production from monocy tes of SLE patients. Spontaneous and IL-10-stimulated PAF production by per ipheral blood monocytes was measured in active (n = 13) and inactive (n = 1 4) SLE patients and in 15 normal control subjects. We observed that monocyt es derived from patients with active SLE, but not from controls or inactive SLE, spontaneously produced significant amounts of PAF. Moreover, IL-10 en hanced the synthesis of PAF from monocytes of active SLE patients only. IL- 10-induced PAF production correlated with the severity of the disease and w ith the extent of proteinuria. These results indicate that IL-10 only stimu lates the synthesis of PAF from monocytes of SLE patients when immunologica lly active, suggesting that IL-10 may possess a paradoxical proinflammatory effect in SLE by promoting the production of PAF, a secondary mediator of inflammation.