Signaling mechanisms of enhanced neutrophil phagocytosis and chemotaxis by the polysaccharide purified from Ganoderma lucidum

Abstract

1 The polysaccharide from Ganoderma lucidum (PS-G) has been reported to enhance immune responses and to elicit antitumor effects. In our previous study, we found that PS-G efficiently inhibited spontaneously and Fas-enhanced neutrophil apoptosis when cultured in vitro. Since phagocytosis and chemotaxis play essential roles in host defense mediated by neutrophils, it is of great interest to know the effect of PS-G on these two cell functions, and the molecular events leading to these actions. 2 Using latex beads and heat-inactive Escherichia coli serving as particles for neutrophil engulfment, we found that PS-G is able to enhance phagocytic activity of human primary neutrophils and neutrophilic-phenotype cells differentiated from all trans retinoic acid-treated HL-60 cells. 3 Chemotactic assay using Boyden chamber also revealed the ability of PS-G to increase neutrophil migration. 4 Exposure of neutrophils to PS-G time dependently caused increases in protein kinase C (PKC), p38 mitogen-activated protein kinase (MAPK), Hck, and Lyn activities. 5 Results with specific kinase inhibitors indicate that phagocytic action of PS-G was reduced by the presence of wortmannin (Phosphatidylinositol 3-kinase, PI3K inhibitor), pyrazolpyrimidine 2 (Src-family tyrosine kinase inhibitor), Ro318220 (PKC inhibitor), and SB203580 (p38 MAPK inhibitor), but not by PD98059 (mitogen-activated protein/ERK kinase inhibitor). Moreover, chemotactic action of PS-G requires the activities of PI3K, p38 MAPK, Src tyrosine kinases and PKC. 6 All these results demonstrate the abilities of PS-G to enhance neutrophil function in phagocytosis and chemotaxis, and further provide evidence to strengthen the beneficial remedy of G. lucidum in human to enhance defense system.