Effects of Brazilian green propolis on double-stranded RNA-mediated induction of interferon-inducible gene and inhibition of recruitment of polymorphonuclear cells.

ABSTRACT

BACKGROUND: Propolis is a bee product with various biological properties, including an antiviral activity when taken orally. However, its mechanisms at the cellular and molecular level are not well understood. RESULTS: We investigated the effect of propolis on antiviral signaling in A549 cells transfected with double-stranded RNA (dsRNA), a model for viral infection. Pretreatment of the cells with propolis inhibited poly IC (synthetic dsRNA)-induced interferon (IFN)-ß expression. Propolis had no effect on the dsRNA-induced expression of RIG-I-like receptors (RLRs), which are known as intracellular viral RNA sensors. As to the effect on antiviral executor genes, propolis enhanced myxovirus resistance 1 (MX1) expression, whereas interferon-inducible gene 6-16 (G1P3) and 2'-5'-oligoadenylate synthetase (OAS) were unaffected. All of these genes belong to the IFN-inducible genes, suggesting that the effect of propolis on antiviral signaling is not necessarily mediated by the autocrine regulation by IFN-ß. Propolis pretreatment inhibited dsRNA-induced interleukin-8 (IL8) and CCL5 expression, and consequently lowered polymorphonuclear leukocyte (PMN) chemotactic activity in the cell-conditioned medium. CONCLUSION: Taken together, these results suggest that propolis may suppress excess inflammatory responses without affecting the innate immunity during viral infection.