EXPRESSION AND HEMOCYTE-TARGETING OF A CAMPOLETIS-SONORENSIS POLYDNAVIRUS CYSTEINE-RICH GENE IN HELIOTHIS-VIRESCENS LARVAE

The polydnavirus associated with the parasitic wasp Campoletis sonoren sis is injected into the lepidopteran insect, Heliothis virescens, dur ing parasitization, after which viral gene products suppress the cellu lar immune system of the hosts. Four related cysteine-rich polydnaviru s genes have been identified in parasitized H. virescens larvae and gr ouped into a family. In this study, we investigated the expression and hemocyte targeting of the cysteine-rich VHv1.4 protein. Full-length a nd truncated VHv1.4 proteins were produced in a bacterial expression s ystem, and the purified proteins were used to raise polyclonal antiser a. In immunoblots the VHv1.4 protein was detected in parasitized insec ts as early as 6 h and throughout the entire course of parasitism. The VHv1.4 protein appeared predominantly in the plasma fraction of hemol ymph from parasitized larvae, suggesting that this protein is secreted . The VHv1.4 protein expressed from a recombinant baculovirus was secr eted in two lepidopteran cell lines and in larvae injected with the re combinant virus. Digestion with endoglycosidases suggests that the VHv 1.4 protein is glycosylated at multiple N-glycosylation sites. Immunof luorescence assays showed that the VHv1.4 protein binds to the hemocyt es, most notably the granulocytes, in H. virescens larvae. After bindi ng, the VHv1.4 protein was internalized, probably by endocytosis. Spec ific binding of the VHv1.4 to granulocytes implies an important functi on in the suppression of host cellular encapsulation response. (C) 199 7 Wiley-Liss, Inc.