IL-10 up-regulates macrophage expression of the S100 protein S100A8

The murine calcium binding protein S100A8 (A8) is a leukocyte chemoattracta nt, but high levels may be protective and scavenge hypochlorite. A8 is indu ced by LPS, IFN-gamma, and TNF in elicited macrophages. Th2 cytokines gener ally suppress proinflammatory gene expression, and IL-4 and IL-13 partially decreased A8 induction in macrophages and endothelial cells stimulated by LPS or IFN. In contrast, IL-10 synergized with LPS and IFN to increase mRNA levels greater than or equal to9-fold and secreted A8 levels similar to4-f old. IL-10 decreased the optimal time of mRNA expression induced by LPS fro m 24 to 8 h. Blocking experiments indicated that endogenous IL-10 contribut es to gene induction by LPS. Cooperation between IL-10 and LPS was not due to altered mRNA stability but was dependent on de novo protein synthesis. T ransfection analysis with A8 luciferase constructs confirmed that synergy w as due to increased transcription. The region of the promoter involved was localized to a 178-bp fragment flanking the transcription start site of the gene. This region was also responsible for the suppressive effects of IL-4 and IL-13. Forskolin, CTP-cAMP, and PGE(2) also enhanced LPS- and IFN-indu ced A8 mRNA, whereas indomethacin significantly reduced synergy between IL- 10 and LPS. Mitogen-activated protein kinase/cyclooxygenase 2/CAMP pathways involving CCAAT-enhancing binding protein, located within the active promo ter, may mediate A8 gene up-regulation in a manner mechanistically distinct to genes regulated by IL-10 via the STAT pathway. A8 exhibits pleiotropic effects, and the high levels secreted as a result of IL-10 synergy may regu late untoward inflammatory damage by virtue of its an antioxidant capacity.