Abstract

Due to the lack of an adaptive immune system, insects rely on innate immune mechanisms to fight against pathogenic infections. Two major innate immune pathways, Toll and IMD, orchestrate anti-pathogen responses by regulating the expression of antimicrobial peptide (AMP) genes. Although the antifungal or antibacterial function of AMPs has been well characterized, the antiviral role of AMPs in insects remains largely unclear. Periplaneta americana ( P. americana ), or the American cockroach, is used in traditional Chinese medicine as an antiviral agent; however, the underlying mechanism of action of P. americana extracts is unclear. Our previous study showed that the P. americana genome encodes multiple antimicrobial peptide genes. Based on these data, we predicted five novel P. americana defensins (PaDefensins) and analyzed their primary structure, secondary structure, and physicochemical properties. The putative antiviral, antifungal, antibacterial, and anticancer activities suggested that PaDefensin5 is a desirable therapeutic candidate against viral diseases. As the first experimental evidence of the antiviral effects of insect defensins, we also showed the antiviral effect of PaDefensin5 in Drosophila Kc cells and Drosophila embryos in vivo . In conclusion, results of both in silico predictions and subsequent antiviral experiments suggested PaDefensin5 a promising antiviral drug.