1). This protein click here synthesis-dependent STAT3 activation, which was reminiscent of findings previously made in the THP-1 monocytic cell line 27, coincided with suppression of the IL-10-induced transcriptional inhibition in monocytes and LPS-conditioned neutrophils, despite unchanged levels of surface IL-10R 26. These findings demonstrate that, at least

in human monocytes and LPS-conditioned neutrophils, de novo protein synthesis is necessary to allow prolonged activation of STAT3 by IL-10, which, in turn, is obligatory for triggering the AIR. It is therefore conceivable that in LPS-conditioned human neutrophils’ protein synthesis is necessary to achieve both the expression of newly made functional IL-10R and the manufacture of unidentified factor(s) that are needed to maintain prolonged STAT3 activation. Candidates for the unidentified factor(s) might include a labile inhibitor of (an) inducible factor(s) that, similarly to suppressor of cytokine signaling-3 (SOCS-3) in the IL-6/IL-6R system,

might negatively regulate STAT3 activation. Accordingly, IL-6 is unable to generate the AIR, despite its capacity to trigger potent, but transient, STAT3 activation 28, 29; however, if SOCS-3 is deleted by gene targeting, then IL-6-mediated STAT3 activation becomes more sustained and able to trigger an AIR indistinguishable MK-8669 chemical structure from that induced by IL-10 30, 31. Clearly, the identification of the regulatory factors involved in the IL-10-signaling cascade, responsible for producing AIR, remains an urgent issue to be solved. In this context, it is interesting to note that a study aimed at identifying the functional relevance of different cytoplasmic domains of human and murine IL-10R1 characterized a stretch of 30 second amino acids within the C-terminal region that seem to be necessary for the anti-inflammatory activities of IL-10 2. It is thus possible that a yet unidentified pathway, involving putative signaling component(s), departs from that specific IL-10R1 region and ultimately modulates cytokine expression in LPS-treated neutrophils incubated with IL-10. Whatever the situation turns out to be, several intracellular and

inducible candidates have already been suggested to mediate IL-10-dependent AIR, including B-cell lymphoma (Bcl)-3 32, heme oxygenase (HO)-1 33, A20-binding inhibitor of NF-κB activation (ABIN)-3 34, one member (IκBNS) of the IκB family of proteins 35, 36, ETV3 (a member of the ETS family of repressors of gene expression) and a transcriptional corepressor Strawberry notch homologue (SBNO)-2 37. In addition, SOCS-3 protein is inducible by IL-10 in human and murine phagocytes 38, 39 and overexpression studies have shown it to mimic IL-10-induced AIR 40. However, the generation of macrophage-specific SOCS3-null mice has excluded the involvement of SOCS3 in mediating the anti-inflammatory or immunoregulatory effects of IL-10 31, 41.