Polysaccharides from Astragalus membranaceus promote phagocytosis and superoxide anion (O2−) production by coelomocytes from sea cucumber Apostichopus japonicus in vitro

The potential immunostimulatory effects of Astralagus membranaceus polysaccharides (APS) on sea cucumber, Apostichopus japonicus (Selenka), were investigated in vitro. Phagocytosis and superoxide anion (O2−) production by phagocytic amoebocytes (PA) from A. japonicus coelomic fluid were measured during incubation at 18 °C, 22 °C, or 25 °C with APS at 0, 10, 20, or 40 μg mL− 1 (n = 3). Phagocytic activity against yeast cells was quantified by direct visualization, and O2− production by nitroblue tetrazolium (NBT) reduction assay. Compared with controls, including APS at 20 μg mL− 1 significantly increased (P < 0.05) the percentage of phagocytic capacity (PC) and phagocytic index (PI) at 18 °C and 22 °C, but no significant enhancement was observed at 25 °C. In contrast, the coelmocytes of A. japonicus can have an obvious generation of O2− after the stimulation. The concentration of 20 μg mL− 1 APS resulted in a significant increase in nitroblue tetrazolium (NBT) positive cells (P < 0.05) at different temperature and even 10 μg mL− 1 APS could increase O2− generation significantly at 18 °C and 22 °C. Both phagocytosing and O2− production increased with the increase of APS concentration from 0 to 20 μg mL− 1 at different temperature, and when APS at 40 μg mL− 1, they were decreased. It suggested that immunocytes activity in A. japonicus decreased with the temperature increasing from 18 °C to 25 °C, and APS could be an effective immunostimulant to enhance phagocytic activity and O2− production.