Immunomodulatory Protein FIP-fve of Flammulina velutipes Activates Murine Dendritic Cells to Regulate T Cell Immune Responses and Acts as a Cancer Vaccine Adjuvant

Golden needle mushroom (Flammulina velutipes) is one of the most common edible mushrooms and has been demonstrated to have many health benefits. FIP-fve is an immunomodulatory protein isolated from F. velutipes and was proved to have an ability to activate many immunocytes such as murine splenocytes, macrophages and hPBMCs. The aim of this study was to demonstrate whether FIP-fve could activate murine dendritic cells and further regulate T cell immune responses, and to investigate its activity as a vaccine adjuvant. The results indicated that FIP-fve could up-regulate surface marker expression of CD40, CD80, CD86, and MHC calss II, and induce cytokines production of TNF-α, IL-1β, IL-6, IL-12, and IL-10 by BMDCs in vitro. We then found that the ability of FIP-fve to activate DCs was remarkably limited in TLR4 knock out mice. These results demonstrated that FIP-fve activated murine DCs mainly through the TLR4 pathway. Furthermore, FIP-fve needed the presence of antigen-presenting cells (APCs) to activate T cell. In the presence of DCs, FIP-fve could induce great amount IFN-γ production and up-regulate the expression of CD25 and CD69 by T cells. Moreover, we isolated CD4+ T cell from OVA-specific DO11.10 mice and cultured with OVA pulsed FVE-treated DCs and OVA antigen. Our data showed that FVE-treated DCs enhanced OVA-specific CD4+ T cell proliferation and IFN-γ production, and demonstrated that FIP-fve could induce TH1 response. On the other hand, we used FIP-fve as a vaccine adjuvant, and found that FIP-fve could induce OVA-specific immune response in vivo. Immunization of mice with OVA pulsed FVE-treated DCs induced antitumor response in a murine MO5 melanoma model and suppressed the tumor growth. According to these findings, we demonstrated that FIP-fve could regulate TH1 cell differentiation through DC maturation and boost antigen-specific immune responses, and enhanced the effect of antitumor response by acting as a dendritic cell vaccine adjuvant.