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The aim of this study was to examine the effect of extracellular polysaccharide (PEP) from Antarctic bacterium Pseudoaltermonas sp. S-5 on RAW 264.7 cells together with the underlying signaling pathways. Our results illustrated that PEP induced dendritic-like morphological change in RAW 264.7 cells, and increased the productions of nitric oxide (NO) and tumor necrosis factor-α (TNF-α). PEP could also enhance phagocytic activity of RAW 264.7 cells. Results of immunofluorescence staining and immunoblotting indicated that PEP caused the nuclear translocation of nuclear factor (NF)-κB subunit p65, the degradation of IκB-α and up-expression of phosphorylated p38 mitogen-activated protein kinase (MAPK) in RAW 264.7 cells. According to pharmacological evaluation with specific enzyme inhibitors, both NF-κB and p38 MAPK signaling pathways were involved in the generation of NO and TNF-α induced by PEP. All these results indicated that PEP from Antarctic bacterium Pseudoaltermonas sp. S-5 activated RAW 264.7 cells through NF-κB and p38 MAPK signaling pathways.

Dendritic cells (DCs) are the key regulators of immune responses. In this study, the effect of an exopolysaccharide (EPS) from the culture broth of Trichoderma pseudokoningii on the phenotypic and functional maturation of murine DCs and its underlying molecular mechanisms were investigated. It showed that EPS induced the morphological changes of DCs and the enhanced expression of DCs featured surface molecules CD11c, CD86, CD80 and major histocompatibility complex II (MHC-II). Flow cytometry analysis showed that the treatment with EPS could reduce FITC-dextran uptake by DCs. Sequentially, the results of ELISA indicated that EPS could increase the production of interleukin-12p70 (IL-12p70) in culture supernatant of DCs. Immunofluorescence staining and western blot analysis further revealed that EPS significantly prompted nuclear factor (NF)-κB subunit p65 translocation, IκB-α protein degradation, and p38 mitogen-activated protein kinase (MAPK) phosphorylation. And the production of IL-12p70 was significantly decreased in condition of the inhibition of p38 or NF-κB signaling pathway. These findings suggested that EPS could induce DCs maturation through both p38 MAPK and NF-κB signaling pathways.