Possible immune functions of congerin, a mucosal galectin, in the intestinal lumen of Japanese conger eel

Congerin, a mucosal galectin of the Japanese conger eel, provides chemical fortification through its agglutinating and opsonizing activity. Congerin is produced in the epidermis, and the epithelia of the oral cavity to the esophagus, but not in the stomach or intestine. We hypothesized that congerin secreted from the upper digestive tract can reach and function in the intestinal lumen. We found that congerin possessed marked resistance against digestion by gastric and enteric enzymes of conger eel. It was not degraded until 6 h of incubation with stomach extract or intestinal digestion juice. Western blotting demonstrated that congerin essentially remained in the intestinal mucus. The mucus agglutinated rabbit erythrocytes, and the agglutination was hampered by anti-congerin antibody. Furthermore, congerin could bind to some enteric bacteria. These results support the above hypothesis.