Comparison of cells free in coelomic and water-vascular system of sea cucumber, Apostichopus japonicus

• We compared cells in the coelomic and water-vascular system of A. japonicus.
• Cell types observed in coelomic also could be found in water-vascular system.
• The total number of coelomocytes was 2–3 times of that in water-vascular system.
• Lymphoid cells were numerically dominant in coelomic, while spherulocytes with pseudopods in water-vascular system.

The sea cucumber, Apostichopus japonicus possesses a variety of cells populating in both the coelomic (cells in the coelomic are called coelomocytes) and water-vascular system. In this study, we compared cells in these two systems of A. japonicus on total cell number, cell types and surface antigens through monoclonal antibodies against coelomocytes. The results demonstrated that the cell types observed in coelomic also could be found in water-vascular system, but the total cell number and percentages of each type were different. The total number of coelomocytes was 2–3 times of that in water-vascular system. Lymphoid cells were numerically dominant in coelomic system, while spherulocytes with pseudopods in water-vascular system. Results of indirect immunofluorescence assay technique showed that both coelomocytes and cells in water-vascular system could be recognized by the corresponding MAbs, and the distribution of its positive signals was not different. In conclusion, cell types and surface antigens in coelomic and water-vascular system were same, but the total cell number and percentages of each type were different. And further researches are needed on whether there are differences in functions of the different composition.