The effects of Steinernema carpocapsae nematode Excreted/Secreted Products on the Adult Drosophila melanogaster Immune Response
Open AccessDrosophila melanogaster is a choice model organism for studying the conserved defense strategies of the innate immune system and their rudimentary roles in relation to human disease. Soil transmitted helminths (STHs) account for a large portion of the globally prevalent neglected tropical diseases (NTDs) that plague impoverished areas with poor sanitation (Mora & Meseeha, 2021). These infections are often lifelong with heavy disease burdens, and closely related entomopathogenic nematodes (EPNs) can be studied within the Drosophila system to investigate their evolutionary conserved mechanism of host immunosuppression. Steinernema carpocapsae is an EPN that rapidly infects and kills a wide range of insect hosts and has been linked to host immunosuppression during the initial stages of infection (Brivio & Mastore, 2018). The lethal nature of a S. carpocapsae infections has previously been credited to its symbiotic bacteria; however, it has become evident that the nematodes are able to effectively kill their hosts independently through their excretion/secretion (ES) products (Lu et al., 2017). Specifically, the aim of this research is to examine how the adult Drosophila immune system is modulated in response to S. carpocapsae ES products in an attempt to ascertain individual pathogenic contributions of the isolated compound to the nematobacterial complex. Injection of a non-dilute 1xES concentration into adult Oregon-R flies significantly altered survival rates killing 93.3% of individuals with the first hour. Next, a diluted working concentration 1/25xES was selected and RT-qPCR data revealed an activation of Imd signaling through a significant increase in the expression of diptericin and metchnikowin. Lastly, Oregon-R males treated with 1/50xES experienced a significant delay in the melanization response and decrease in hemocyte numbers compared to their female counterparts indicating that there are sex specific differences in response to the ES products. By studying this isolated compound, we were able to identify potential targets within the host immune system that are being capitalized by the nematode. These findings are beneficial as they promote the discovery of new areas of research for developing new immunotherapies in clinical settings or further exploiting this novel information for improving agricultural method for pest management.
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