IL-10 MODULATES CYTOKINE GENE TRANSCRIPTION BY PROTEIN SYNTHESIS-INDEPENDENT AND DEPENDENT MECHANISMS IN LIPOPOLYSACCHARIDE-TREATED NEUTROPHILS

We have recently reported that the ability of IL-10 to rapidly exert its anti-inflammatoryeffects on human neutrophils is dependent upon exposure of these cells to LPS for atleast 3–4 h. Here, we demonstrate that, in neutrophils "preconditioned" by LPS, IL-10primarily targets the transcription of TNF-a, CXCL8 and IL-1ra genes, as revealed byprimary transcript real-time RT-PCR. We also show that IL-10-induced transcriptionalrepression of TNF-a and CXCL8 genes consists of two distinct phases: an early one,occurring rapidly and in a protein synthesis-independent manner, followed by a secondphase, more delayed and dependent on protein synthesis. Interestingly, the proteinsynthesis dependence of the latter phase coincides with a reduced ability of IL-10 toinduce STAT3 tyrosine phosphorylation. Importantly, inhibition of IL-10-inducedSTAT3 activation and IL-10-suppressive action by a prolonged exposure tocycloheximide (CHX) was observed to occur also in human monocytes and wascaused by a defective IL-10-mediated activation of Jak1 and Tyk2 kinases. Takentogether, our findings suggest that CHX interferes with the IL-10-mediated intracellularsignaling pathway by interrupting events upstream of STAT3 activation. These dataquestion the concept of the requirement of an IL-10-induced mediator as the uniquemechanism to execute IL-10 anti-inflammatory program.