Bombyx mori C-Type Lectin 16 Inhibits BmNPV Proliferation by Degrading Viral Protein Bm9 via Ubiquitin–Proteasome System

C-type lectins (CTLs) are proteins with carbohydrate-recognition domains. These macromolecules interact with pathogen components, thereby playing important roles in the immune system. Current studies indicate that silkworm CTLs are involved in Bombyx mori nucleopolyhedrovirus (BmNPV) infection. Nevertheless, the molecular mechanisms through which these CTLs affect viral infection remain unclear. In this study, B. mori C-type lectin 16 (BmCTL16) was identified in the silkworm. Its expression was significantly downregulated upon BmNPV infection. Functional assays showed that BmCTL16 overexpression suppressed BmNPV proliferation, whereas its knockdown enhanced BmNPV proliferation. Protein–protein interaction assays confirmed that BmCTL16 interacts with BmNPV protein Bm9 in the cytoplasm. Notably, BmCTL16 promoted the degradation of Bm9 via the ubiquitin–proteasome system. Knockdown of Bm9 by siRNA significantly reduced BmNPV proliferation, confirming that Bm9 is the key target for BmCTL16 to exert its antiviral function. Collectively, this study reveals a novel CTL-mediated antiviral mechanism. BmCTL16 interacts with Bm9 and promotes its ubiquitin–proteasome degradation, thereby inhibiting viral proliferation. Furthermore, BmNPV evades this host defense by downregulating BmCTL16 expression. These findings enhance our understanding of silkworm CTL-mediated antiviral defense and offer novel perspectives on host–virus interactions in B. mori.