Cellular and humoral responses are important in inhibiting the systemic infections by pathogens. Cellular responses include phagocytosis, encapsulation and nodule formation, while humoral immunity includes primarily the secretion of antimicrobial peptides (AMPs) such as defensin, cecropin-1 and -2, gambicins. Cellular responses are mediated by plasmatocytes and granulocytes, while AMPs are produced by fat body and hemocytes; as well as the midgut and a cluster of cells at the foregut/midgut junction, known as proventriculus (cardia). AMPs have been shown to be induced upon microbial challange in many insects. We have been working on humoral immunity in several different models such as the Leptinotarsa decemlieneta, and two major pests of grain in Turkey, the Wheat stinkbug and the sunnpest (Eurygaster maura). We identified various novel AMPs in these pests using proteom, transcriptome and RNAi analyses from the fat body and midgut upon microbial challange by various pathogens such as Bacillus thuringiensis.
The insect peritrophic matrix and vertebrate mucusal layer share also defensive proteins such as mucins. Our studies revealed presence of different types of insect intestinal mucins based on their structural domain organizations in the lepidopteran models. A type denoted “complex mucins” associated with the bertha armyworm peritrophic matrix are targeted during baculovirus infection by a metalloprotease encoded by the viral genome, while the “binary type mucins” are not. Such findings had great potential in terms of development of more effective baculoviruses via recombination technology. Indeed, our collaborators in Canada (Drs. Dwayne Hegedus, Martin Erlandson and David Theilmann) developed a recombinant baculovirus encoding the baculoviral metalloprotease and found that it was almost 4.5 times more effective than the wild strain baculovirus. We currently work on development of a new baculovirus formulation targeting the mucin functioning via chemical reagents. This formulation technology was already tested both in the laboratory and was found to significantly improve baculovirus efficacy up to 30-40%. Fundamentally, it could be applied to other lepidopteran hosts, as it targets the essential features of the common defense components of the lepidopteran peritrophic matrix. In particular, understanding the resistance mechanism of binary type mucins against metalloproteases is a current interest for us right now.