In either case, see more an immunomodulatory effect of antibiotics would further support a contribution of the host immune response in larval susceptibility
to B. thuringiensis. This is the third study, each with a different lepidopteran species, to report that ingestion of B. thuringiensis leads to alterations in hemocytes [41, 42]. It remains unclear, however, whether the observed changes in hemocytes directly contribute to larval mortality or if they merely reflect changes in immune status. Interestingly, Ericsson et al.  reported that T. ni larvae resistant to B. thuringiensis had significantly fewer hemocytes than did susceptible larvae. Further experiments are needed to determine whether hemocytes are functionally required in susceptibility. Such experiments should include a comparison of the effect of ingestion of B. thuringiensis on hemocytes between larvae with and without enteric bacteria. In addition, while our work shows that immunogenic peptidoglycan fragments can restore B. thuringiensis susceptibility in larvae lacking gut bacteria, we do not know whether co-ingestion of peptidoglycan and B. thuringiensis leads to changes in hemocytes, nor have we identified the final immune effectors of B. thuringiensis-induced killing. However, the delayed mortality
Selleckchem RG7420 of larvae fed B. thuringiensis in EVP4593 solubility dmso combination with some antioxidants and eicosanoid inhibitors suggests that production of reactive oxygen species could be involved. Interestingly, hemocytes have been shown to be key regulators of the oxidative burst upon infection, particularly by promoting activation of the phenoloxidase cascade [68, 69], which might be caused by hemocyte rupture [70, 71]. The parallels between the progression of disease and mortality caused by B. thuringiensis with that in mammalian sepsis are noteworthy. Disease and death associated with mammalian sepsis are believed to be caused by uncontrolled host production of local immune mediators leading to local and systemic inflammatory responses [52, 72, 73]. Peptidoglycan induces the innate
immune system of both invertebrates and vertebrates [45–49] and contributes to almost both sepsis and B. thuringiensis-induced killing in gypsy moth larvae. Eicosanoids and reactive oxygen and nitrogen species are critical in the innate immune response in mammals and treatments for sepsis often target these compounds [59, 74–77]. In gypsy moth larvae, inhibitors of eicosanoid biosynthesis and antioxidants prevent or slow disease progress, suggesting a role of innate immunity. There is increasing evidence that diseases of animals are frequently caused by multiple microbial species. These polymicrobial infections often include members of the indigenous microbiota and lead to complex interactions with the host immune system . Using Drosophila as a model of cystic fibrosis, Sibley et al.