Insect immunity: A genetic factor (hrtp) is essential for antibacterial peptide expression in Drosophila after infection by parasitoid wasps

We have used a parasitoid wasp Drosophila melanogaster system to investigat e the relationship between the humoral and cellular immune responses in ins ects. Expression of the gene encoding diptericin, an antibacterial peptide in various D. melanogaster strains parasitized by several species of parasi toid wasps, was studied by Northern blot. These strains have the capacity t o encapsulate parasitoid eggs. Two strains appeared to produce diptericin m RNA after parasitoid challenge, regardless of their cellular immune reactio n to the wasp species. This suggests that a specific genetic factor, or fac tors, here designated humoral response to parasitoid (hrtp), is present in these two strains of D. melanogaster and is implicated in the expression of the antibacterial gene after parasite infection. This hrtp genetic factor is recessively expressed and located on the second chromosome, suggesting t hat it is monofactorial. The transgenic strain Dipt.2.2-lacZ:1, in which th e transgene is present on the first chromosome, is normally susceptible to the parasitoid wasp. The chromosome bearing the hrtp factor was transferred to this transgenic strain, which then became reactive when triggered by wa sp infection. The hrtp factor appears necessary for the activation of dipte ricin by the parasitoid wasp. No correlation between the cellular immune ca pacity and the humoral response was observed, suggesting that the two compo nents of insect immunity are regulated independently. (C) 2000 Wiley-Liss, Inc.