Arsenite suppresses NO production evoked by lipopolysaccharide and poly(I:C) via the suppression of interferon-β expression in RAW264.7 cells.

Immunological functions are disturbed in humans who have been chronically exposed to arsenic via contaminated groundwater. Little is known about the specific mechanisms underlying the impairment of immunological defense system caused by arsenic. The activation of macrophage cells upon infection with bacteria and viruses plays important roles in the defense against these pathogens. Here we show that exposure to arsenite (As(III)) suppresses nitric oxide (NO) production in murine RAW264.7 macrophage cells stimulated with lipopolysaccharide (LPS) and poly(I:C), the compounds mimicking bacterial and viral infection, respectively. As(III) suppressed the LPS- or poly(I:C)-evoked induction of inducible NO synthase (iNOS) without affecting the transactivation of NF-κB. As the interferon (IFN)-β/STAT1 pathway is also involved in the induction of iNOS in addition to NF-κB, we examined the effects of As(III) on the expression and secretion of IFN-β, the expression of the components of IFN-α/β receptor, the phosphorylation of STAT1, and the levels of cytokines involved in STAT1 activation. The results showed that the expression and secretion of IFN-β were specifically suppressed by As(III) treatment in RAW264.7 cells stimulated with LPS or poly(I:C). These results suggest that As(III) suppresses the expression and secretion of IFN-β, leading to the reduced STAT1 activation and consequently the reduced iNOS induction in macrophage cells. Our data suggest an important role of the arsenic-induced suppression of IFN-β on the disturbances in immunological defense against both bacteria and viruses.