Flow cytometry analysis of softness syndrome effects on hemocytes of the tunicate Halocynthia roretzi

The mortality of the tunicate Halocynthia roretzi due to softness syndrome, which exhibits tunic thinning as well as loss of muscle elasticity, has caused serious problems for the aquaculture industry in Korea. The effects of softness syndrome can be better understood by studying the defense mechanisms of Halocynthia roretzi. This study used flow cytometry to assess hemocyte parameters in H. roretzi. Flow cytometry provided a means to rapidly quantify tunicate defense mechanisms by measuring temperature and zymosan-dependent effects on phagocytosis activity.Also, immune parameters, such as morphology of cell sub-populations (size and granularity), total hemocyte counts (THC), hemocyte viability, and phagocytosis activity using flow cytometry analysis, of normal tunicates and softness syndrome tunicates were compared. The results showed that, in normal tunicates, the phagocytic rate and hemocyte viability are higher than those of tunicates with softness syndrome. Total hemocyte numbers in softness syndrome tunicates were 4 times higher than that of normal tunicates.It is suggested that the tunicate immune system is associated with softness syndrome and that flow cytometry is a powerful tool for characterizing immune response.