A serpin from the parasitoid wasp Leptopilina boulardi targets the Drosophila phenoloxidase cascade

The insect phenoloxiclase (PO) cascade is known to be tightly regulated by serine proteases and serine protease inhibitors of the serpin family. As a key component of the insect immune system, it is also suspected to be inhibited by several endoparasitoid wasps, insects that develop inside other arthropods as hosts. However, the underlying mechanisms of this inhibition are largely undescribed. Here, we the characterization of a gene encoding a serpin, LbSPNy, highly expressed in the venom of the wasp Leptopilino boulardi (ISy type), and we show that either the venom or the recombinant LbSPNy inhibit the PO cascade in the hemolymph of Drosophila yakuba host larva. Altogether, our results identify the first serpin used as a virulence factor by a parasitoid wasp and show that it disrupts the activation pathway the PO in the Drosophila host. (c) 2008 Elsevier Ltd. All rights reserved.