A novel LRR domain-containing C-type lectin gene with immune regulatory functions protects Penaeus vannamei against Vibrio parahaemolyticus infection.

C-type lectins (CTLs), a vital group of soluble pattern recognition receptors (PRRs), are essential to the shrimp's innate immune system. However, little is known about the CTLs composed of a C-type lectin domain (CTLD) and another domain. In this study, a novel C-type lectin containing a leucine-rich repeat (LRR) domain, designated LRRCTL, was identified in Penaeus vannamei and found to exhibit immune regulatory functions. First, LRRCTL expression was highest in the hepatopancreas. The mRNA expression levels of LRRCTL showed a significant upregulation under the different stimuli, including Vibrio parahaemolyticus, Staphylococcus aureus, Aspergillus niger, Lipopolysaccharide (LPS). Second, knockdown of the expression of LRRCTL increased the bacterial load of V. parahaemolyticus, whereas injection of rLRRCTL or r△LRR-LRRCTL recombinant proteins enhanced the survival rate of V. parahaemolyticus-infected shrimp. Additionally, the knockdown of LRRCTL expression reduced the mRNA level of multiple immune-related genes, encompassing both immune signaling components and antimicrobial peptide genes, suggesting an important role in immune regulation. Our findings reveal that LRRCTL is essential for regulating humoral immune responses, particularly antimicrobial peptide production, against V. parahaemolyticus infection. The findings provide a theoretical foundation for further investigation into the functional mechanisms of composite CTLs in shrimp innate immunity and potential molecular targets for developing strategies to prevent and control shrimp diseases.