The diamondback moth, Plutella xylostella, is reluctant to a baculovirus, Autographa california nucleopolyhedrosis virus (AcNPV) at its oral administration. However, parasitization by an endoparasitoid wasp, Cotesia plutellae, enhances the viral susceptibility. This study analyzed an antiviral activity of P. xylostella in response to the viral infection and determined the parasitic factor inhibiting the antiviral mechanism. For the analysis of antiviral activity of P. xylostella, a recombinant AcNPV expressing enhanced green fluorescence (AcNPV-EGFP) was orally adminstered to lavae of P. xylostella. After 24 h, EGFP expression was observed in the midgut tissue at a confocal-FITC mode. At the same time, a characteristic midgut melanotic response (MMR) was observed in some midgut regions under a phase contrast microscope. Thereafter, the EGFP signal was attenuated, while MMR spread on most midgut region. When the MMR was scored from 0 to 5 by the intensity of melanized cell density, it increased in time- and dose-dependent manners at the viral administration per os. These results suggest that the MMR is an antiviral activity of P. xylostella. This antiviral activity was significantly attenuated by C. plutellae parasitism. The parasitized P. xylostella showed significant decrease in the MMR score compared to nonparasitized larvae when they were orally administered with the same dose of AcNPV. To determine the parasitic factor(s) inhibiting the antiviral activity from the symbiotic polydnavirus of C. plutellae (C. plutellae bracovirus: CpBV), CpBV-IkB, which is a viral homolog of NFkB inhibitor and has been considered as an antiviral factor as in other polydnaviruses, was tested. A recombinant AcNPV expressing CpBV-IkB (AcNPV-IkB) was constructed and administered to P. xylostella larvae. As expected, AcNPV-IkB significantly decreased the antiviral activity measured by the MMR score compared to AcNPV-EGFP treatment. This study suggests that CpBV-IkB plays an antiviral parasitic role in the molecular interactions between P. xylostella and C. plutellae.

Newcastle disease virus(NDV) 감염된 baby hamster kidney(BHK) 세포에서 syncytium(합포체) 형성은 세포막 표면으로의 수송된 바이러스 당단백질 hemagglutinin-neuramidase(HN)에 의해 일어난다. HAU 값은 추출물의 농도가 25과 3.2 ug/mL 사이에서는 현저하게 감소하였으나, NDV 감염된 HAD(%)는 25 ug/mL 농도에서 광범위한 흡착능의 감소를 나타내 바이러스 당단백질의 세포내 생합성은 저해되지 않았다. 그러므로, 약용식물인 마황 메탄올 추출물이 바이러스 당단백질의 세포막으로의 수송과 함께 합포체 형성을 저해하여 항바이러스 작용을 하였다. 또한 마황 추출물의 저해활성을 조사한 결과 α-glucosidase에 대한 추출물의 IC50은 18μg/mL이었으며, β-glucosidase, α-mannosidase, β-mannosidase에 대한 마황 추출물의 IC50은 각각 60, 40, 150μg/mL로 나타나 β-type glycosidases 보다 α-type glycosidase에 대한 효소활성 저해능이 우수하였다. 따라서 IC50농도에서는 세포내에서 당단백질 생합성은 저해되지 않으며 당단백질의 수송을 저해하는 것으로 판단되었으며 향후 항바이러스 관련 작용기작의 연구가 필요하다고 판단된다.

We aimed to investigate the antiviral activity of Zanthoxylum species against influenza virus A/WS/33, A/PR/8 and B/Lee/40 used by sulforhodamine B (SRB) assay and the action of leaves extracts of Zanthoxylum piperitum on life cycle of influenza virus A/WS/33. Among the twelve extracts, only the leaf extract of Z. piperitum exhibited strong antiviral activity at low concentration of less than 10μg/ml with no citotoxicity (50μg/ml) against all of three viruses. In addition, only oseltamivir showed antiviral activity with IC50 of 65.3μg/ml against influenza A/WS/33 among the viruses. Furthermore, the leaf extract of Z. piperitum suppressed infection of influenza virus A/WS/33, when added just prior (-1 hr) or after virus inoculation (0 hr). Leaf extract of Z. piperitum directly affect the infectivity of influenza virus A/WS/33 particles. Therefore, Leaf extract of Z. piperitum exhibited higher antiviral activity against three influenza viruses than that of the oseltamivir, which directly interacts with influenza A/WS/33 particles, affecting the initial stages of infection such as receptor binding and virus entry.