Synergistic actions of complement and lysozyme in clearance of Escherichia coli from amphioxus Branchiostoma belcheri

Amphioxus appears to lack free circulating blood cells. How it clears invading pathogens from its body remains unknown to date. We demonstrate here that amphioxus Branchiostoma belcheri is capable of efficiently eliminating the invading bacterium Escherichia coli from its humoral fluid, and the complement and lysozyme are both involved in the elimination of the invading pathogen. Both the complement and lysozyme act in concert against the invading bacterium, but the complement appears to play a more dominant role than the lysozyme.