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 (O(2)(-)) production by phagocytic amoebocytes (PA) from A. japonicus coelomic fluid were measured during incubation at 18 degrees C, 22 degrees C, or 25 degrees C with APS at 0, 10, 20, or 40 microg mL(-1) (n=3). Phagocytic activity against yeast cells was quantified by direct visualization, and O(2)(-) production by nitroblue tetrazolium (NBT) reduction assay. Compared with controls, including APS at 20 microg mL(-1) significantly increased (P<0.05) the percentage of phagocytic capacity (PC) and phagocytic index (PI) at 18 degrees C and 22 degrees C, but no significant enhancement was observed at 25 degrees C. In contrast, the coelmocytes of A. japonicus can have an obvious generation of O(2)(-) after the stimulation. The concentration of 20 microg mL(-1) APS resulted in a significant increase in nitroblue tetrazolium (NBT) positive cells (P<0.05) at different temperature and even 10 microg mL(-1) APS could increase O(2)(-) generation significantly at 18 degrees C and 22 degrees C. Both phagocytosing and O(2)(-) production increased with the increase of APS concentration from 0 to 20 microg mL(-1) at different temperature, and when APS at 40 microg mL(-1), they were decreased. It suggested that immunocytes activity in A. japonicus decreased with the temperature increasing from 18 degrees C to 25 degrees C, and APS could be an effective immunostimulant to enhance phagocytic activity and O(2)(-) production.