Calnexin functions in antibacterial immunity of Marsupenaeus japonicus

• Calnexin (MjCnx) was identified in kuruma shrimp Marsupenaeus japonicus.
• MjCnx is upregulated in hemocytes, intestine and hepatopancreas after Vibrio anguillarum challenge.
• MjCnx exists in the cytoplasm and on the surface of shrimp hemocytes.
• MjCnx has binding specificity to different polysarccharides on surface of bacteria.
• MjCnx can enhance bacterial clearance by promoting hemocyte phagocytosis.

Calnexin (Cnx) is an endoplasmic reticulum membrane–bound lectin chaperone that comprises a dedicated maturation system with another lectin chaperone calreticulin (Crt). This maturation system is known as the Cnx/Crt cycle. The main functions of Cnx are Ca2+ storage, glycoprotein folding, and quality control of synthesis. Recent studies have shown that Cnx is important in phagocytosis and in optimizing dendritic cell immunity. However, the functions of Cnx in invertebrate innate immunity remain unclear. In this research, we characterized Cnx in the kuruma shrimp Marsupenaeus japonicus (designated as MjCnx) and detected its function in shrimp immunity. The expression of MjCnx was upregulated in several tissues challenged with Vibrio anguillarum. Recombinant MjCnx could bind to bacteria by binding polysaccharides. MjCnx protein existed in the cytoplasm and on the membrane of hemocytes and was upregulated by bacterial challenge. The recombinant MjCnx enhanced the clearance of V. anguillarum in vivo, and the clearance effects were impaired after silencing MjCnx with RNA interference assay. Recombinant MjCnx promoted phagocytosis efficiency of hemocytes. These results suggest that MjCnx functions as one of the pattern recognition receptors and has crucial functions in shrimp antibacterial immunity.