Antibacterial Immune Proteins in Insects — A Review of Some Current Perspectives

Abstract

More than 10⁶ insect species are recognized in the literature and estimates indicate that the number of individual insects is as high as 10¹⁸ [32]. These high numbers predict that insects will have very effective immune systems, if not they would not be as numerous as they are. The large number of insect species also creates a need for the selection of model systems. Many investigators have used larvae of the greater wax moth, Galleria mellonella and vaccination of this insect was reported already 60 years ago. However, hemolymph from rapidly growing larvae contains a large number of proteins and when comparing Galleria to diapausing pupae of Hyalophora cecropia we found the latter superior both for immunological work and for purification of proteins [11]. The cecropia pupae are large, they weigh 5–10 g, and they contain 1 –2 ml of hemolymph. When a diapausing pupa is immunized it turns on predominantly the genes for immunity while the rest of the animal remains in a dormant state. Immunized pupae of cecropia are, therefore, a system for biological enrichment of the RNA and the proteins which are synthesized from the genes for immunity. We have taken advantage of this fact both in the purification of 15 different immune proteins and in the isolation of immune RNA, later to be used for the preparation of a cDNA bank. During the last 5 years we have carried out parallel sequence work on the protein and DNA level. This program has so far produced the complete amino acid sequences for five cecropins, one lysozyme, and one attacin. In addition, we have obtained cDNA sequences corresponding to one lysozyme, one cecropin, and the two major forms of attacin.