Unpaired ( upd)-3 expression and other immune-related functions are stimulated by interleukin-8 in Drosophila melanogaster SL2 cell line

Abstract

Invertebrate innate immunity relies on both 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). In Drosophila melanogaster, the cytokine Unpaired (Upd)-3, is known to activate the JAK/STAT pathway, but it is still not clear which molecules and pathways are responsible for its induction and secretion. It has been proposed that highly chemotactic factors may increase the expression of upd-3. In this respect, we have studied the effects of the chemotactic human recombinant (hr) interleukin (IL)-8 on the immune functions of Drosophila SL2 macrophage-like cells. The hrIL-8 increases the percentage of phagocytic cells with a specific timing and enhances the expression of the cytokine, upd-3, as well as that of the putative cytokine Drosophila helical factor ( dhf). The antimicrobial peptides defensin, cecropin A1 and diptericin, are all influenced in their expression by the human chemokine, while hrIL-8 leaves unaffected the expression of drosomycin, i.e. the antimicrobial peptide more strictly connected with the Toll pathway. Similar effects to those registered for hrIL-8 are also provoked by a specific activator of the Imd pathway, i.e. the Escherichia coli peptidoglycan. RNAi experiments demonstrated that the silencing of the Imd pathway-associated kinase dTAK1, leaves unaffected the induction of upd-3, while it completely abolishes the effects of hrIL-8-on the expression of dhf. Our data suggest that the Imd pathway is not fundamental in regulating the levels of upd-3, whereas it controls the expression of the putative cytokine dhf.