Membrane attack complex/perforin-like (MACPF) proteins perform key roles in vertebrate innate immunity. Torso-like (Tsl) is the only known MACPF protein in Drosophila melanogaster, discovered for its developmental role in terminal patterning of the embryo. We have discovered an additional role for Tsl in the Drosophila immune response. Well established immune response assays were conducted by infecting a tsl null mutant with various strains of bacteria and observing survival post-infection. We have shown that tsl null mutants have a defective immune response to gram-positive, but not gram negative bacteria. This is extremely unexpected, since the mammalian membrane attack complex targets gram-negative bacteria through disruption of the outer bacterial membrane. Gram-positive bacterial cell walls have a different composition and upon infection are detected by distinct Drosophila pattern recognition proteins. It therefore seems likely that tsl performs a different role in the fly immune system than that of vertebrate MACPF proteins involved in immune defence. This result is suggestive of a role for Tsl in the Toll signalling pathway, however further experiments showed that tsl null mutants can successfully induce transcriptional targets of the pathway.  Ongoing experiments are testing whether tsl functions in cellular immunity, acting to assist the phagocytosis of pathogens. It is also of interest to investigate if Tsl interacts with the same genetic pathway(s) or partner proteins as it does in development to determine the similarities and/or differences in Tsl function between these processes.