Mytilus edulis hemolymph agglutinin,3) and Helix pomatia agglutinin4) had opsonic activity and that lectin-like substances in the serum functioned as a non-self recognition

This study was undertaken to identify an opsonin in the coelomic fluid of Strongylocentrotus nudus by separating several humoral defense factors using galactose-affinity chromatography. A galactose-binding-protein had no opsonic activity against rabbit and sheep erythrocytes, whereas the galactose-unadsorbed fraction and hemolysin fraction separated by affinity adsorption onto formaldehyde-fixed ghosts of sheep erythrocytes possessed significant opsonic activity against both erythrocytes. The opsonic and hemolytic activities of the hemolysin fraction were inactivated at the same temperature (50•Ž) at which the opsonic acitivity of the fresh coelomic fluid was lost. The opsonic activity of the hemolysin fraction was inhibited by complement inhibitors such as hydrazine and threonine. These results suggest that a hemolysin in the coelomic fluid mainly plays an important role as an opsonin in the initial internal defense system.