<i>Bmlebocin3</i> could inhibit <i>Bombyx mori</i> cytoplasmic polyhedrosis virus in silkworms via the <scp>immune deficiency</scp> pathway and through the <scp>20‐hydroxyecdysone</scp> modulations

Antimicrobial peptides (AMPs) are critical components of the innate immune system in insects, but their regulation and contribution to antiviral defence remain poorly understood. In this study, we investigated the expression, antiviral activity and regulation of Bombyx mori Lebocin-3 (BmLEB3) during infection with Bombyx mori cytoplasmic polyhedrosis virus (BmCPV). BmLEB3 expression was markedly induced following BmCPV infection in the silkworms. RNAi-mediated knockdown of BmLEB3 increased the transcriptional level of viral marker gene vp1 in BmN cells, whereas overexpression led to the inhibition of viral replication in BmN cells. Mechanistically, BmCPV induced the expression of the pattern-recognition receptor BmPGRP-S1 and the transcription factor BmRelish, and silencing of either gene reduced BmLEB3 expression, suggesting that immune deficiency (IMD)-associated signalling contributes to BmLEB3 regulation. Moreover, BmLEB3 was induced by 20-hydroxyecdysone (20E) treatment, further strengthening its antiviral effect. Molecular docking analysis revealed a potential interaction between 20E and BmPGRP-S1, indicating a possible hormonal modulation of IMD-associated AMP expression. Collectively, our results identify BmLEB3 as a virus-responsive AMP and suggest that its expression is modulated by IMD-associated signalling and hormonal cues during BmCPV infection in B. mori. These findings provide insight into the molecular regulation of antiviral immune responses in the silkworm and provide a basis for improving disease resistance in sericulture against microbial pathogens.