A POLYDNAVIRUS-ENCODED PROTEIN OF AN ENDOPARASITOID WASP IS AN IMMUNESUPPRESSOR

The molecular mechanism by which polydnaviruses of endoparasitoid wasp s disrupt cell-mediated encapsulation reactions of host insects is lar gely unknown. Here we show that a polydnavirus-encoded protein, produc ed from baculovirus and plasmid expression vectors, prevents cell surf ace exposure of lectin-binding sites and microparticle formation durin g immune stimulation of haemocytes. The inactivation of immune-related cellular processes by this protein was analysed using a specific lect in and annexin V and shown to be virtually identical to polydnavirus-m ediated effects on haemocytes. Cytochalasin D application has similar effects on haemocytes, suggesting that the immune suppression by the p olydnavirus protein is caused by the destabilization of actin filament s. Since the exposure of cell surface glycoproteins and the formation of microparticles are part of an immune response to foreign objects or microorganisms and a prerequisite for cell-mediated encapsulation of microorganisms and parasites, the virus-encoded protein may become an important tool for the inactivation of cellular immune reactions in in sects and an essential component in understanding immune suppression i n parasitized host insects.