Biochemical and cytological evaluation of the coelomic fluid of Urechis unicinctus: Its responses under pathogenic exposure and potential phagocytic activities

Abstract

To characterize the immune functions of the coelomic fluid of echiuran worms (Urechis unicinctus), their cellular composition and biochemical index were initially analyzed. Meanwhile, the phagocytic activity of coelomocytes and the impact of pathogenic infection immuno-related enzymes were explored. Lastly, coelomocyte density and humoral immune factor levels were detected under pathogenic conditions. The results revealed three major coelomocyte types in the coelomic fluid, comprising granular cells, hyaline cells and thrombocytes. Granulosa cells exhibited ability to adsorb and phagocytose with bacteria, whereas hyaline cells and thrombocytes manifested no adsorption and phagocytosis abilities. Additionally, numerous immune factors (such as albumin, alanine aminotransferase, and alkaline phosphatase) were detected in the coelomic fluid. Following pathogenic stimulation, the coelomocyte density and level of humoral immune factors (SOD, LSZ, ACP, and AKP) were changed. Collectively, the results suggested that humoral immune factors and coelomocytes were sensitive to environmental factors. Taken together, our study indicated that coelomocytes, in conjunction with immune factors in the coelomic fluid, formed an immune barrier in U. unicinctus.