Polydnavirus‐mediated inhibition of lysozyme gene expression and the antibacterial response

Abstract

Parasitism of lepidopteran host larvae by hymenopteran parasitoids impairs the cellular immune response via expression of polydnavirus genes. Encapsulation of parasitoid eggs is thereby prevented. Parasitized insects are susceptible to opportunistic infections, suggesting that additional components of the immune system are affected. Insects normally respond to infection by inducing the synthesis of an array of antibacterial factors, including cecropins and lysozyme via a NFkappaB/lkappaB-like signal transduction pathway. To characterize the effects of PDVs on the antibacterial immune response, plasma antibacterial activities were assayed in H. virescens larvae infected with the C. sonorensis PDV. Plasma lysozyme activity in Heliothis virescens was reduced in parasitized and PDV-infected larvae after immune challenge. To examine the regulation of lysozyme after CsPDV injection, the Heliothis virescens lysozyme cDNA was cloned. In contrast to plasma lysozyme activity, the 1.1 kb lysozyme mRNA was induced in fat body and haemocytes by known elicitors. The data suggest that CsPDV, like some other viruses, regulates host cell gene expression at the level of translation. We propose that the immunodeficiencies caused by CsPDV injection are caused, in part, by the targeted translational inhibition of specific humoral immune response transcripts.

Antibacterial activity of lysozyme in the desert locust, Schistocerca gregaria (Orthoptera: Acrididae)

“…This has similarly been reported in holometabolous insects, e.g., PGN in M. sexta (Kanost et al, 1988), B. mori (Morishima et al, 1995) and S. cynthia ricini (Fujimoto et al, 2001), and LPS in S. eridania (Anderson & Cook, 1979), Heliothis virescens (Shelby et al, 1998) and G. mellonella (Fiolka, 2012). However, it is uncertain which of the molecular components of these conjugated carbohydrates (PGN and LPS) act as elicitors (Marmaras & Lamproulou, 2009).…”

Analysis of ESTs generated from immune-stimulated hemocytes of larval Heliothis virescens

“…No ESTs corresponded to the known antibacterial and antifungal proteins of H. virescens such as attacin (Ourth et al, 1994), heliomicin (Lamberty et al, 1999), virescin (P83416), viresin (Chung and Ourth, 2000), heliocin (P83427), cecropins-A (P83413), -B (P83414), -C (P83415), or lysozyme (Shelby et al, 1998). Unlike the Spod-Xtox ortholog, these bactericidal proteins are likely to be synthesized predominantly, or exclusively, in the fat bodies and so would not have been adequately sampled by our hemocyte EST effort.…”

Viral infection induces different detoxification enzyme activities in insecticide-resistant and -susceptible brown planthopper <i>Nilaparvata lugens</i> strains

“…38) Endoparasitoid wasps have a symbiotic DNA virus, a polydnavirus (PDV), which regulates the host immune system by the gene expression of the polydnavirus in the host cells when it is injected into a suitable lepidopteran host along with an egg. 39,40) Although P450 activity increased in susceptible males infected with RRSV, no significant difference was observed relative to buffer-injected individuals. However, RGSV infection increased the P450 activity in both males and females, indicating that infection by RGSV induced the increase in P450 activity.…”