Molecular and Functional characterization of a novel C-type lectin during WSSV infection in Eriocheir sinensis.

C-type lectins (CTLs) are key pattern recognition receptors in innate immunity; however, their functions during white spot syndrome virus (WSSV) infection remain to be elucidated. Here, we identified a novel CTL gene from Chinese mitten crab (Eriocheir sinensis), designated as EsLec2. EsLec2 encodes a protein with a conserved carbohydrate-recognition domain (CRD) and shows phylogenetic clustering with other crustacean CTLs. RNA interference (RNAi) and recombinant protein (rEsLec2) injection assays revealed that EsLec2 downregulates ie1 and vp28 expression, indicating that it suppresses WSSV replication. Further studies revealed that upon WSSV infection, EsLec2 positively regulates STAT transcription, antimicrobial peptide (AMP) expression, and phenoloxidase (PO), acid phosphatase (ACP), and alkaline phosphatase (AKP) activities, while upregulating autophagy-related genes expression. In contrast, EsLec2 suppresses the expression of nucleocytoplasmic transport genes, which can be exploited by the virus. These findings suggest that EsLec2 suppresses WSSV replication via a dual mechanism: activating humoral immunity and autophagy, while simultaneously preventing viral hijacking of the host nuclear transport system. Collectively, this study expands our understanding of invertebrate CTLs in antiviral defense and provides potential molecular targets for WSSV control in crustacean aquaculture.