In vivo and in vitro study of immunomodulatory activities of mushroom sclerotial polysaccharides

Mushroom sclerotia have a rich source of polysaccharides when compared with fruit bodies. It was previously reported that the polysaccharides from novel mushroom sclerotia, namely, Pleurotus tuber-regium and Polyporus rhinocerus, had potent in vitro and in vivo antitumor effects. In this project, hot water-soluble sclerotial polysaccharides of Pleurotus tuber-regium (PTRW), hot water-soluble and sonication-assisted cold alkali-soluble sclerotial polysaccharides of Polyporus rhinocerus (PRW and PRSon, respectively) were chosen for investigation of their in vivo and in vitro immunomodulatory effects.;The in vivo immunomodulatory study was carried out by injecting the abovementioned sclerotial polysaccharides intraperitoneal to 7-8 weeks old healthy male BALB/c mice. The spleens excised from groups injected with PTRW and PRW were found to have significant increase of weight ( p<0.001). Flow cytometric analysis revealed that the NK cell population in spleen mononuclear cells (MNCs) of mice injected with PRW and PRSon was increased when compared with the control. In addition, ail three sclerotial polysaccharides showed a large increase of T helper cell population as well as CD4+/CD8+ ratio in spleen MNCs. On the other hand, the macrophage population in peritoneal exudates cells (PEC) was found to be increased in the groups of mice injected with PTRW and PRW.;In vitro antitumor study indicated that PTRW had a significant (p<0.05) inhibitory effect (>40%) on the human monocytic leukemic cells (THP-1) in addition to HL-60 and K562 cells. In vitro immunomodulatory study showed that both PRW and PRSon had significant proliferative effects (p<0.05) on human normal spleen monocyte/macrophage cell, MD. Moreover, PRSon was shown to have a significant increase (p<0.05) in the growth of human natural killer cells, NK-92M1; however, PTRW showed a significant inhibition (p<0.05) on this cell line.;Polysaccharides have long been proposed to exert their antitumor and thus immunomodulating functions through glucan receptors and among the four being discovered, Dectin-1 has drawn most attention recently. In the in vivo study, PRSon showed an increase in the expression of Dectin-1 on mice spleen MNCs while PTRW showed an increase in the expression of the previously widely-reported complement receptor (CR3). There was also an increase of Dectin-1 expression on PEC in the mice injected with PRSon. In the in vitro study, the three mushroom sclerotial polysaccharides were incubated with NK-92M1, MD and THP-1 cells. There was a significant increase (p<0.05) of Dectin-1 expression on NK-92MI cells incubated with PTRW. On the other hand, PTRW caused a significant decrease ( p<0.05) of Dectin-1 expression while PRSon showed a significant increase (p<0.05) on THP-1 cells. The cytokine profile of extra-cellular media indicated that the inhibition of THP-1 cells by PTRW should be related to the innate immunity. In the in vitro study, human primary immune cells, CD56+ NK cells were used to incubate with sclerotial polysaccharides and there was a significant stimulation (p<0.05) of their growth when compared with the control.;Athymic nude mice were employed as the in vivo model to study the detailed mechanism of how the three sclerotial polysaccharides act to inhibit the growth of human xenografted tumors in vivo. Using immunohistochemical staining, it was found that the presence of F4/80 + macrophages was related to the reduction of tumor size of the HL-60 xenograft. mRNA extracted from the spleens were reverse-transcribed to cDNA and detected by real-time PCR so that a variety of genes related to the toll-like receptors being up-regulated or down-regulated due to the injection of mushroom sclerotial polysaccharides were determined. Combining the results from dectin-1 regulation, it was concluded that both hot water-soluble sclerotial polysaccharides, PTRW and PRW, having a structure of polysaccharide-protein complexes were responsible for activating and thus binding to CR3 or toll-like receptors while PRSon with structure of pure beta-glucan was responsible for activating the expression of dectin-1 receptor, which led to the subsequent activation of host immune system in immunopotentiation and antitumor activities.;In the future, further investigation of the detailed structure of mushroom sclerotial polysaccharides is required to explain the immunomodulatory mechanism so that the effective dosage for immunomodulation as well as antitumor effects can be determined. Furthermore, phage display can be applied to find out any novel glucan receptors specific to the mushroom sclerotial polysaccharides.