Our findings also implicate the serine protease inhibitor Spn27A in promoting ethanol-induced hyperactivity. In early development, Spn27A targets the Easter serine protease that cleaves and activates the Toll ligand Spätzle. In adults, Spn27A acts on 2 different serine proteases, MP1 and MP2, to regulate the activation of phenoloxidase in the production of melanin during bacterial infection (Tang et al., 2006). The target for Spn27A in ethanol responses is not known. While Easter is dispensable for immune responses, it is expressed in adult heads, and Spn27A has been shown to interact with the Toll pathway by an as yet incompletely understood mechanism during bacterial infection (Ligoxygakis et al., 2002). Moreover, we were unable to detect any gross increase in melanization in adult flies lacking Spn27A following ethanol exposure, as occurs in infection (De Gregorio et al., 2002), despite escalating the dose and number of exposures (not shown). While not conclusive, these data suggest that Spn27A expression regulation by ethanol exposure may utilize this immunity pathway in a manner distinct from bacterial infection. In addition, infection-induced immune responses are limited to the
