Abstract:Similar to hemocytes in other species, coelomocytes of sea urchins play an important role in the immune system. A verification of the recovery pattern and origin of coelomocytes would be vital in understanding its immune mechanism. Axial organ is a glandular organ that has been thought to be the hemopoietic tissue of sea urchin. Using monoclonal antibodies against coelomocytes, we demonstrated in a previous study that axial organ could serve as a storage tissue of coelomocytes. We further investigated the recovery pattern of coelomocytes in the sea urchin Strongylocentrotus intermedius and the changes in the axial organ during the recovery phase. Coelomocyte density was examined at 6 h, 12 h, 18 h, and 24 h after manual extraction of 10% body weight of celomic fluid. Histology of the axial organ was observed, and cell proliferation activity was detected with a monoclonal antibody against Ki-67 (cell proliferation antigen). Results showed that the average coelomocyte density at 6 h was significantly lower than that before extraction; it gradually decreased at 12 h, with a density slightly lower than the initial level, with a recovery value of (92.78±29.40)%. Average coelomocyte was significantly higher than the initial level at 18 h, with a recovery value of (137.08±32.40)%, and was significantly higher than that at 6 h and 12 h (P<0.05). Subsequently, the coelomocyte density gradually decreased. The inter-tissue of the axial organ declined and cavitation occurred after coelomocytes were lost. The outer epithelial layer became loose and broke off, and vacuolation was observed in the bulges of the epithelial layer. The inter-tissue increased at 18 h, and newborn tissue appeared clearly at 24 h. Using the Ki-67 antibody, we found a cell production signal in the axial organ from the normal sea urchin and the signal was significantly enhanced after 18 h. Our results indicated that the restoring mechanism of coelomocytes could initiate rapidly after coelomocyte loss, while histological changes and cell production activity enhancement may occur in the axial organ. The present study provides valuable references for further research on the origin and ontogenesis of coelomocytes.
