Effect of lipopolysaccharide on in vitro phagocytosis by hemocytes from giant freshwater prawn (Macrobrachium rosenbergii)

When separate batches of Macrobrachium rosenbergii hemocytes were cultured in different media at 25 degrees C for 40 min, the percentage of viable hem ocytes cultured in modified M-199 medium (M-199; 80%) was significantly hig her than the percentage cultured in modified crayfish saline (M-CFS; 65%), although wide individual variation was noted. The percentage of phagocytic cells increased significantly with lipopolysaccharide (LPS) concentrations up to 16 mu g/mL, but no further significant increases were found at concen trations from 16 to 100 mu g/mL. Microscopy of phagocytosis in hemocytes cu ltured in M-199 and induced with LPS at a final concentration of 20 mu g/mL showed that target zymosan particles (1-4 mu m) were engulfed by granulocy tes (GC) and semigranulocytes (SGC), but were only attached to and not engu lfed by hyaline cells (HC). However, smaller sized fluorescent-labeled bead s (0.5 mu m) were primarily phagocytosed by HC. This suggests that all thre e types of hemocytes from IM. rosenbergii are able to phagocytose foreign p articles. Microscopy showed that LPS significantly altered hemocyte morphol ogy by increasing pseudopodia stretching and hemocyte size and it also incr eased the number of engulfed particles per phagocyte. The percentage of HC positive for two lysosomal enzymes (acid phosphatase and alpha-naphthyl ace tate esterase) related to phagocytosis was higher than that of positive SGC or GC.