Scavenger receptor B1 mediates phagocytosis and the antimicrobial peptide pathway in the endoparasitic wasp Micropilits mediator.

Scavenger receptors (SRs) are a family of pattern recognition receptors (PRRs) in the immune system. They are required for phagocytosis and act as co-receptors of Toll-like receptors to regulate immune signaling pathways in the fight against pathogens. Little is known about the function of SRs in insects. Here, we reported on a member of the SR family from the parasitic wasp Micropilits mediator (designated MmSR-B1) that is responsive to bacterial infection. The recombinant extracellular CD36 domain of MmSR-B1 produced in Escherichia coli cells is capable of binding to peptidoglycans and bacterial cells, causing agglutination of bacteria. Furthermore, we demonstrated that double-stranded RNA-mediated knockdown of MmSR-B1 impedes hemocyte phagocytosis and downregulates the expression of antimicrobial peptide (AMP) genes defensins and hymenoptaecins. Knockdown of MmSR-B1 led to increased death of the wasps when challenged by bacteria. Our study suggests that MmSR-B1 mediates phagocytosis and the production of AMPs in M. mediator wasps.