Effects of Brazilian Green Propolis on Double-Stranded RNA-Mediated Induction of Interferon-Inducible Gene and Inhibition of Recruitment of Polymorphonuclear Cells

BACKGROUND: Propolis is a bee product with various biological properties including an antiviral activity when orally taken. However, its mechanisms at the cellular and molecular level are not well understood.

RESULTS: We investigated the effect of propolis on the antiviral signaling in A549 cells transfected with double-stranded RNA (dsRNA), a model for viral infection. Pretreatment of the cells with propolis inhibited the poly I:C (synthetic dsRNA)-induced interferon (IFN)-β 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 while 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-β. Propolis pretreatment inhibited the dsRNA-induced interleukin-8 (IL8) and CCL5 expression, and consequently lowered the 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.