Perlucin, a novel C-type lectin from the mud crab Scylla paramamosain, modulates innate immunity and enhances tolerance to Vibrio parahaemolyticus infection and ammonia stress.

C-type lectins (CTLs), a pivotal family of PRRs, are essential for mediating host immune defense via specific recognition of exogenous pathogenic microbes. A new perlucin family member (designated SpPer), a typical member of the CTL superfamily, was cloned and characterized from the mud crab Scylla paramamosain. The complete coding region of SpPer was 582 bp in length, encoding a 193-amino acid protein that harbors a single carbohydrate-recognition domain (CRD), a signature structural feature of CTLs. Tissue-specific expression profiling confirmed prominent SpPer enrichment in the hepatopancreas and gill of healthy mud crabs. Quantitative real-time PCR assays demonstrated that SpPer mRNA transcription was induced in the hepatopancreas following Vibrio parahaemolyticus infection and ammonia nitrogen exposure, suggesting its potential involvement in immune responses and environmental stress adaptation. To elucidate the regulatory mechanism of SpPer, in vivo silencing was performed using RNA interference (RNAi). Following SpPer silencing, transcript abundances of several immune effector genes (anti-lipopolysaccharide factor, ALF; crustin antimicrobial peptide, crustin; Toll-like receptor, Toll; heat shock protein 70, HSP70; and superoxide dismutase, SOD) were significantly decreased, suggesting that SpPer played a vital role in immune defense by regulating genes involved in pathogen killing, signaling transduction, cellular protection, and antioxidant defense. Functional assays showed that SpPer silencing impaired bacterial clearance in the hemolymph and impaired the survival ability of mud crabs upon V. parahaemolyticus infection. Furthermore, under ammonia nitrogen stress, SpPer silencing led to a remarkable rise in cumulative mortality relative to the untreated control group. Taken together, these observations illustrate that SpPer is essential for regulating innate immune defense against bacterial infection and enhancing tolerance to ammonia stress in S.paramamosain.