Identification and characterisation of five innate immune genes in the cabbage looper Trichoplusia ni

Sammanfattning: When insects are infected with bacteria, they respond by producing a range of different antibacterial peptides and by activating protease cascades leading to coagulation and melanisation. Cellular defence mechanisms are also involved in killing of microorganisms through phagocytosis and encapsulation.We have found several genes that are upregulated upon bacterial infection in the cabbage looper, Trichoplusia ni, by using the differential display method. Attacin and gloverin are antibacterial proteins previously known from other insect species. Both are glycine-rich proteins that act by disrupting the permeability barrier of the cell membrane.An azurocidin homologue without serine protease activity is expressed exclusively in the insect gut. It is induced by injection of bacteria and by feeding larvae with bacteria. Two amino acid substitutions, serine to glutamate and histidine to serine, in the catalytic triad explain the lack of protease activity.Another protein induced by a bacterial infection is a 3-dehydroecdysone 3b-reductase-like protein (DERH). This protein was detected in integument and hemolymph of T. ni larvae. In addition, it is developmentally regulated. A possible function for DERH is to convert 3-dehydroecdysone into ecdysone, regulating the titer of biologically active ecdysteroids in the larvae.Furthermore, a peptidoglycan recognition protein (PGRP) is upregulated in T. ni by bacterial infection. PGRP is a peptidoglycan- and bacteria binding protein, possibly involved in immune recognition. Homologues were also cloned from mouse and man. The mouse PGRP also binds peptidoglycan, suggesting a functional conservation of the protein from insects to humans.