Ficus carica polysaccharides promote the maturation and function of dendritic cells

Abstract

Various polysaccharides purified from plants are considered to be biological response modifiers and have been shown to enhance immune responses. Ficus carica L. is a Chinese traditional plant and has been widely used in Asian countries for its anti-tumor properties. Ficus carica polysaccharides (FCPS), one of the most essential and effective components in Ficus carica L., have been considered to be a beneficial immunomodulator and may be used in immunotherapy. However, the immunologic mechanism of FCPS is still unclear. Dectin-1 is a non-toll-like pattern recognition receptor, predominately expressed on dendritic cells (DCs). Activation of DCs through dectin-1 signaling can lead to the maturation of DC, thus inducing both innate and adaptive immune responses against tumor development and microbial infection. In our study, we found that FCPS could effectively stimulate DCs, partially through the dectin-1/Syk pathway, and promote their maturation, as shown by the up-regulation of CD40, CD80, CD86, and major histocompatibility complex II (MHCII). FCPS also enhanced the production of cytokines by DCs, including IL-12, IFN-γ, IL-6, and IL-23. Moreover, FCPS-treated DCs showed an enhanced capability to stimulate T cells and promote T cell proliferation. Altogether, these results demonstrate that FCPS are able to activate and maturate DCs, thereby up-regulating the immunostimulatory capacity of DCs, which leads to enhanced T cell responses.

Figure 1

FCPS activate Syk via dectin-1 in BMDCs. (A) Expression of dectin-1 on BMDCs. Anti-dectin-1 antibody (thick line) or rat IgG2b (solid gray) were used to stain dectin-1 on BMDCs and then analyzed by flow cytometry; (B,C) Syk was activated after FCPS stimulation via the dectin-1 pathway; (B) Cells were stimulated with FCPS (100 μg/mL) and dectin-1 was blocked with an anti-dectin-1 antibody (5 μg/mL). Cells were lysed and P-Syk levels (upper band) were analyzed by western blot with β-actin as a loading control (lower band); (C) Quantitation of the P-Syk/β-actin ratio. Results are shown as means ± SD from threeindependent experiments. ** p < 0.01, N.S. no significance.

Figure 2

FCPS activate and maturate DC, partially through the dectin-1 pathway. (A–H) BMDCs were stimulated with FCPS (100 μg/mL) with (E–H) or without (A–D) anti-dectin-1 antibody or ratIgG (5 μg/mL) for 48 h. Cells were stained with specific Abs against CD40, CD80, CD86, and MHCII, and then analyzed via flow cytometry. The values shown in the histograms are geometric mean fluorescence intensities (GeoMFI). Results are shown as means ± SD from three independent experiments. *** p < 0.001, ** p < 0.01.

Figure 3

FCPS alter the expression of multiple cytokines secreted by BMDCs. (A–D) BMDCs were stimulated with FCPS (100 μg/mL) for 24 h with or without anti-dectin-1 antibody or rat IgG (5 μg/mL). Cells were collected and mRNA levels of IL-12p35 (A); IFN-γ (B); IL-6 (C); and IL-23p19 (D) were measured by qRT-PCR. All data are shown as means ± SD from three independent experiments. *** p < 0.001, N.S. no significance.

Figure 4

FCPS enhances the immunostimulatory capacity of DCs. BMDCs were stimulated with FCPS (100 μg/mL) for 48 h. Cells were harvested and treated with mitomycin C and then co-cultured with CD4⁺CD25⁻ Teff cells in the presence of anti-CD3 mAb for 72 h. The proliferation was measured via the MTT assay. Results are presented as means ± SD from three independent experiments. * p < 0.05.