TLR4-mediated activation of macrophages by the polysaccharide fraction from Polyporus umbellatus(pers.) Fries

Aim of the Study: Zhu Ling (Polyporus umbellatus) is well-known to reduce the risk of a variety of diseases. In this study, we explored the molecular mechanism of its immunostimulatory potency in immune responses of macrophages, using polysaccharides prepared from Polyporus umbellatus (PPS). Materials and methods: Splenocyte proliferation was analyzed with H-3-TdR incorporation method. Nitric oxide (NO) was measured by Griess method and cytokines of culture supernatants was detected by enzyme linked immunosorbent assay (ELISA). The fluoresceinamine-labeled PPS (Flu-PPS) and dextran (Flu-dextran) were prepared by the cyanogen bromide activation method. The cell-binding activity of Flu-PPS was analyzed with FACS and confocal microscopy. NF-kappa B activity was measured by ELISA assay. Results: We found that PPS is able to strongly upregulate the functions of macrophages such as Nitric oxide (NO) production and cytokine expression. Compared with C3H/HeJ group, PPS significantly stimulated the proliferation of splenocytes and the production of TNF-alpha, IL-1 beta and NO of peritoneal macrophages from C3H/HeN mice. The function blocking antibodies to TLR-4, but not TLR-2 and CR3, markedly suppressed PPS-mediated TNF-alpha and IL-1 beta production. Flow cytometric and confocal laser-scanning microscopy analysis shown that fluorescence-labeled PPS (f-PPS) can bind specifically to the target cells, and the binding can blocked by unlabeled PPS and anti-TLR4, but not anti-TLR2 and CR3 monoclonal antibodies. Nuclear translocation and DNA binding activity of NF-kappa B was significantly induced by PPS. Conclusions: Therefore, our data suggest that PPS may exert its immunostimulating potency via TLR-4 activation of signaling pathway. (C) 2010 Elsevier Ireland Ltd. All rights reserved.