Gut SCP is an immune-relevant molecule involved in the primary immunological memory or pattern recognition in the amphioxus Branchiostoma belcheri.

To understand the role of calcium-binding proteins of invertebrates in immunological response, amphioxus sarcoplasmic calcium-binding protein (SCP) was investigated in the present study. Following gene cloning, recombinant protein expression and purification and antibody preparation, the expression and alteration of SCP in the response to bacterial challenge were detected using Western blotting. SCP was not detected in the branchia, humoral fluid, gonad or in the gut of wounded animals, but it was abundant in muscle and appeared in the gut of healthy animals using Vibrio parahaemolyticus immunization and challenge. Furthermore, whether gut SCP possessed anamnestic response was investigated using cross-immune challenge between Gram-positive and -negative bacteria. Gut SCP showed stronger anamnestic activity or pattern-recognition in response to Gram-negative bacterium V. parahaemolyticus than Gram-positive bacterium Staphylococcus aureus. The response was faster and more species-specific to V. parahaemolyticus, whereas it was slower and longer to S. aureus. The reason why the response showed significant difference between Gram-positive and -negative bacteria awaits investigation. These results indicate that gut SCP is an immune-relevant molecule involved in the primary immunological memory or pattern recognition in the amphioxus Branchiostoma belcheri.