Up-regulation of IL-10R1 expression is required to render human neutrophils fully responsive to IL-10

We have recently shown that IL-10 fails to trigger Stat3 and Stat1 tyrosine phosphorylation in freshly isolated human neutrophils. In this study, we r eport that IL-10 can nonetheless induce Stat3 tyrosine phosphorylation and the binding of Stat1 and Stat3 to the IFN-gamma response region or the high -affinity synthetic derivative of the c-sis-inducible element in neutrophil s that have been cultured for at least 3 h with LPS. Similarly, the ability of IL-10 to up-regulate suppressor of cytokine signaling (SOCS)-3 mRNA was dramatically enhanced in cultured neutrophils and, as a result, translated into the SOCS-3 protein. Since neutrophils' acquisition of responsiveness to IL-10 required de novo protein synthesis, we assessed whether expression of IL-10R1 or IL-10R2 was modulated in cultured neutrophils. We detected c onstitutive IL-10R1 mRNA and protein expression in circulating neutrophils, at levels which were much lower than those observed in autologous monocyte s or lymphocytes. In contrast, IL-10R2 expression was comparable in both ce ll types. However, IL-10R1 (but not IL-10R2) mRNA and protein expression wa s substantially increased in neutrophils stimulated by LPS. The ability of IL-10 to activate Stat3 tyrosine phosphorylation and SOCS-3 synthesis and t o regulate IL-1 receptor antagonist and macrophage-inflammatory protein 1 b eta release in LPS-treated neutrophils correlated with this increased IL-10 R1 expression, and was abolished by neutralizing anti-IL-10R1 and anti-IL-1 0R2 Abs. Our results demonstrate that the capacity of neutrophils to respon d to IL-10, as assessed by Stat3 tyrosine phosphorylation, SOCS-3 expressio n, and modulation of cytokine production, is very dependent on the level of expression of IL-10R1.