A C-type lectin of Helicoverpa armigera maintains the stability of the hemolymph microbiota by regulating the expression of lysozyme

An increasing body of evidence suggests that the insect hemolymph is not a sterile environment and that various nonpathogenic microorganisms can stably or transiently inhabit the hemolymph in many insect species. However, little is currently known about how the insect immune system maintains microbial homeostasis within the hemolymph. In this study, a C-type lectin of Helicoverpa armigera (HaCTL6) was shown to be involved in maintaining the stability of the hemolymph microbiota. The expression of H. armigera antimicrobial peptide (AMP) genes was down-regulated after RNAi of HaCTL6. Moreover, the knockdown of HaCTL6 resulted in a decrease in the antibacterial activity and an increase in the total bacterial load of the hemolymph. Transcriptome analysis showed that a lysozyme (HaLysozyme-like) was significantly down-regulated after HaCTL6 RNAi. Moreover, the knockdown of HaLysozyme-like led to a decrease in the antibacterial activity and an increase in the total bacterial load of the hemolymph. Furthermore, the injection of recombinant HaLysozyme-like into the hemocoel caused a significant reduction in the total number of bacteria in the hemolymph. These results indicate that HaCTL6 may regulate the homeostasis of bacteria in the hemolymph by utilizing HaLysozyme-like as an effector.