IFN-α as an Adjuvant for Adenovirus-Vectored FMDV Subunit Vaccine through Improving the Generation of T Follicular Helper Cells

IFN-alpha exhibits either direct antiviral effects or distinct immunomodulatory properties, which was identified as a 'natural immune adjuvant' for both the innate and the adaptive immune responses. Here we have investigated the effects of IFN-alpha as an adjuvant on the generation of T follicular helper (Tfh) cells and antigen-specific antibody responses. The data showed that adenoviral vectors co-expressing FMDV VP1 proteins and porcine IFN-alpha potently enhanced the generation of Tfh cells, the secretion of IL-21 protein and the expression of Bcl-6 mRNA, compared with adenoviral vectors sole expressing VP1 alone. Additionally, IFN-alpha substantial increased the number of germinal-center (GC) B cells and formation of GCs. Furthermore, IFN-alpha enhanced the antibody response, as shown by increased production of all IgG and subclasses of IgG1 and IgG2a. Thus, our results revealed the potent adjuvant activity of IFN-alpha which enhanced the generation of Tfh cells and regulated the humoral immunity by promoting germinal-center reactions and antibody responses.