Abstract

Scavenger receptor class B (SR-B) is a class of transmembrane glycoproteins involved in insect innate immunity through the recognition of pathogen-associated molecular patterns (PAMPs). Although extensively studied in vertebrates, the precise molecular mechanisms by which SR-B mediates immune responses in insects remain unclear. In this study, we identified and characterized an SR-B member from Ostrinia furnacalis . We report that OfSR-B1 localizes to the hemocyte membrane of O. furnacalis , and its expression is upregulated following infection with Micrococcus luteus and Pseudomonas aeruginosa . In vitro assays demonstrated that recombinant OfSR-B1 protein binds to both Gram-positive and Gram-negative bacteria and promotes bacterial agglutination. Knockout of O. furnacalis OfSR-B 1 suppressed the transcription of a calcium channel protein, and pre-incubation with an OfSR-B1 antibody inhibited bacteria-induced Ca 2+ influx. Transcriptomic analysis revealed that OfSR-B 1 knockout impaired intracellular signaling in the Toll pathway and phagocytosis. Following OfSR-B 1 RNA interference or antibody blockade, the expression of genes related to the Toll pathway, antimicrobial peptides ( Attacin and Gloverin ), and phagocytosis decreased. Further phagocytosis assays confirmed that the loss of OfSR-B 1 impaired hemocyte-mediated bacterial phagocytosis. Finally, the OfSR-B 1 knockout reduced larval survival following bacterial infection. These findings elucidate the role of OfSR-B1 in bacterial recognition and its underlying immune mechanisms, providing valuable insights for the development of biopesticides targeting the OfSR-B1 protein.