POLYDNAVIRUS-MEDIATED INHIBITION OF LYSOZYME GENE-EXPRESSION AND THE ANTIBACTERIAL RESPONSE

Parasitism of lepidopteran host larvae by hymenopteran parasitoids imp airs the cellular immune response via expression of polydnavirus genes . Encapsulation of parasitoid eggs is thereby prevented. Parasitized i nsects are susceptible to opportunistic infections, suggesting that ad ditional components of the immune system are affected, Insects normall y respond to infection by inducing the synthesis of an array of antiba cterial factors, including cecropins and lysozyme via a NF kappa B/I k appa B-like signal transduction pathway. To characterize the effects o f PDVs on the antibacterial immune response, plasma antibacterial acti vities were assayed in H. virescens larvae infected with the C. sonore nsis PDV, Plasma lysozyme activity in Heliothis virescens was reduced in parasitized and PDV-infected larvae after immune challenge. To exam ine the regulation of lysozyme after CsPDV injection, the Heliothis vi rescens lysozyme cDNA was cloned. In contrast to plasma lysozyme activ ity, the 1.1 kb lysozyme mRNA was induced in fat body and haemocytes b y known elicitors. The data suggest that CsPDV, like some other viruse s, regulates host cell gene expression at the level of translation. We propose that the immunodeficiencies caused by CsPDV injection are cau sed, in part, by the targeted translational inhibition of specific hum oral immune response transcripts.