title: Venom of parasitoid, Pteromalus puparum, suppresses host, Pieris rapae, immune promotion by decreasing host C-type lectin gene expression.
abstract: BACKGROUND
  Insect hosts have evolved immunity against invasion by parasitoids, and in co-evolutionary response parasitoids have also developed strategies to overcome host immune systems. The mechanisms through which parasitoid venoms disrupt the promotion of host immunity are still unclear. We report here a new mechanism evolved by parasitoid Pteromalus puparum, whose venom inhibited the promotion of immunity in its host Pieris rapae (cabbage white butterfly).
  
  
  RESULTS
  A full-length cDNA encoding a C-type lectin (Pr-CTL) was isolated from P. rapae. Quantitative PCR and immunoblotting showed that injection of bacterial and inert beads induced expression of Pr-CTL, with peaks of mRNA and Pr-CTL protein levels at 4 and 8 h post beads challenge, respectively. In contrast, parasitoid venom suppressed Pr-CTL expression when co-injected with beads, in a time and dose-dependent manner. Immunolocalization and immunoblotting results showed that Pr-CTL was first detectable in vesicles present in cytoplasm of granulocytes in host hemolymph, and was then secreted from cells into circulatory fluid. Finally, the secreted Pr-CTL bound to cellular membranes of both granulocytes and plasmatocytes. Injection of double-stranded RNA specific for target gene decreased expression of Pr-CTL, and a few other host immune-related genes. Suppression of Pr-CTL expression also down-regulated antimicrobial and phenoloxidase activities, and reducing phagocytotic and encapsulation rates in host. The inhibitory effect of parasitoid venom on host encapsulation is consistent with its effect in suppressing Pr-CTL expression. Binding assay results showed that recombinant Pr-CTL directly attached to the surface of P. puparum egges. We infer that Pr-CTL may serve as an immune signalling co-effector, first binding to parasitoid eggs, regulating expression of a set of immune-related genes and promoting host immunity.
  
  
  CONCLUSIONS
  P. puparum venom inhibits promotion of host immune responses by silencing expression of host C-type lectin gene Pr-CTL, whose expression affected transcription of other host immune-related genes.
authors: State Key Laboratory of Rice Biology & Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Ministry of Agriculture, Institute of Insect Sciences, Zhejiang University, Hangzhou, China.
authors: Qi
authors: Q
authors: Fang
authors: Fei
authors: F
authors: Wang
authors: John A
authors: JA
authors: Gatehouse
authors: Angharad M R
authors: AM
authors: Gatehouse
authors: Xue-xin
authors: XX
authors: Chen
authors: Cui
authors: C
authors: Hu
authors: Gong-yin
authors: GY
authors: Ye
mesh_terms: D000818:Animals; D002080:Butterflies / Q000276:immunology / Q000469:parasitology*; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D006790:Host-Parasite Interactions / Q000276:immunology*; D007109:Immunity / Q000235:genetics; D037181:Lectins, C-Type / Q000235:genetics*; D014862:Wasp Venoms / Q000276:immunology / Q000633:toxicity*; D014863:Wasps / Q000472:pathogenicity*
chemical_list: D037181:Lectins, C-Type; D014862:Wasp Venoms