hrIL-8 stimulates unpaired (upd)-3 expression and other immune-related activities in Drosophila melanogaster SL2 cell line

cellular and humoral components. Among humoral factors, there is less information on soluble molecules able to act as signals during the immune response (i.e. cytokines). To date, only a few cytokines have been observed in different arthropod taxa such as insects (Spätzle and Unpaired [Upd]-3) and crustaceans (astakine). As it has been proposed that a possible involvement of chemotactic factors may increase the expression of upd-3, we have studied the effects of human recombinant ilnterleukin-8 (hrIL-8) on the immune functions of Drosophila melanogaster SL2 macrophage-like cells. We have found that hrIL-8 enhances the expression of upd-3 and of the putative cytokine, Drosophila helical factor (dhf). Furthermore, hrIL-8 promotes the transcription of the antimicrobial peptide genes defensin and cecropin A1. Beside these evidences on humoral factors, hrIL-8 also increases the phagocytic activity of SL2 cells. Our data suggest the existence in D. melanogaster of one or more soluble factors that possibly share some structural similarity with IL-8, eliciting an immune response involving simultaneously cellular and humoral components.