Innate immunity is the first line of defence against infectious micro-organisms, and the basic mechanisms of pathogen recognition and response activation are evolutionarily conserved. In mammals, the innate immune response in combination with antigen-specific recognition is required for the activation of adaptive immunity. Therefore, innate immunity is a pharmaceutical target for the development of immune regulators. Here, for the purpose of pharmaceutical screening, we established an in vitro culture based on the innate immune response of Drosophila. The in vitro system is capable of measuring lipopolysaccharide (LPS)-dependent activation of the immune deficiency (imd) pathway, which is similar to the tumour necrosis factor signalling pathway in mammals. Screening revealed that well-known inhibitors of phospholipase A(2) (PLA(2)), dexamethasone (Dex) and p-bromophenacyl bromide (BPB) inhibit LPS-dependent activation of the imd pathway. The inhibitory effects of Dex and BPB were suppressed by the addition of an excess of three (arachidonic acid, eicosapentaenoic acid and gamma-linolenic acid) of the fatty acids so far tested. Arachidonic acid, however, did not activate the imd pathway when used as the sole agonist. These findings indicate that PLA(2) participates in LPS-dependent activation of the imd pathway via the generation of arachidonic acid and other mediators, but requires additional signalling from LPS stimulation. Moreover, PLA(2) was activated in response to bacterial infection in Sarcophaga. These results suggest a functional link between the PLA(2)-generated fatty acid cascade and the LPS-stimulated imd pathway in insect immunity.

We have observed the direct light emission from the slow mode of surface plasmon polaritons (SPP) of metal-insulator-metal (MIM) tunnel junctions formed on a ultra-fine grating. The grating (period=100 nm, groove depth=12 nm, area=200 µm×200 µm) was created on a Si(100) wafer, using a direct electron beam lithography technique and wet etching of SiO2 The MIM junction was formed by evaporation of Al and Au films on this grating. The emission peak for the Al-Oxide-Au junction was observed at 1.55 eV that is expected from the dispersion curve of the slow mode. The spectral width is appreciably narrower than the emission due to the natural residual micro-roughness of the junction.