Envelope Protein of Parasitic Wasp Symbiont Virus, Polydnavirus, Protects the Wasp Eggs from Cellular Immune Reactions by the Host Insect

Abstract

Cotesia kariyai polydnavirus (CkPDV) virions are present in the oviducts of C. kariyai wasp and are injected with eggs into the hemocoel of the host armyworm Pseudaletia separata larvae during parasitization. Evidence that the presence of polydnavirus particles on the surface of the wasp eggs may be essential for prevention of cellular immune reactions by the host hemocytes was obtained by isolating an immunoevasive factor from CkPDV virions. The purified proteinaceous factor protects foreign materials from adhesion and encapsulation by hemocytes of the host P. separata larvae but not by those of common cutworm Spodoptera litura larvae which is an incompatible host for the C. kariyai wasp. Purification procedures consisted of extraction with ethanol/trifluoroacetic acid and reverse-phase high performance liquid chromatography. A factor with a molecular mass of approximately 50 kDa is demonstrated to be present on the envelope of CkPDV virion by immunoelectronmicroscopic observations. Furthermore, immunoreactive proteins are found in plasma of the armyworm larvae but not in the common cutworm larvae, indicating that only the natural host of C. kariyai wasp shares a similar epitope with CkPDV. The sequence of 23 amino acid residues at the amino terminus of the factor was determined to be Ile-Ser-Val-Glu-Asn-Val-Xaa-Thr-Thr-Gly-Ile-Phe-Leu-Asp-Ser-Gly-Glu-Xaa- Val- Pro-Tyr-Ala-Thr-Lys-Pro.