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

Abstract 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 3 H-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-κB 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-α, IL-1β 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-α and IL-1β 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-κB was significantly induced by PPS. Conclusions Therefore, our data suggest that PPS may exert its immunostimulating potency via TLR-4 activation of signaling pathway.