Enhancement of antigen-specific humoral immune responses and protein solubility through conjugation of bacterial flagellin, Vibrio vulnificus FlaB, to the N-terminus of porcine epidemic diarrhea virus surface protein antigen S0

Oh, Seo-ho; Kim Cho, Young-Saeng; Lee, Ho-Bin; Lee, Sang-Mok; Kim, Whee-Soo; Hong, Liang; Cho, Chong-Su; Choi, Yun-Jaie; Kang, Sang-Kee

To protect piglets, the main contributor to substantial economic loss, it is imperative to immunize sows to establish the passive immunity of piglets via colostrum/milk. Therefore, enhancement of the PEDV-specific humoral immune response is a prerequisite for PED vaccine development. Flagellin has been used as a fusion adjuvant for a broad range of recombinant antigens in past decades [11, 12, 14] ; however, there have been relatively few studies assessing the effect of the flagellin fusion position on its adjuvant activity. Therefore, we tested the ability of S0-F and F-S0 to induce S0-specific humoral immune responses in mice. Interestingly, as shown in Fig. 4B -E, we confirmed that flagellin exerts a differential adjuvant effect depending on its conjugation position in reference to S0. The S0-specific antibodies in Fig. 4 is inferred to be the neutralizing antibodies, as the PEDV neutralization titers have positive correlations to indirect ELISA results which use S0 produced from E. coli as a coating protein [29] . We used Complete Freund's adjuvant (CFA) and incomplete Freund's adjuvant (IFA) together with our conjugated vaccine system in all mice immunization experiments equally as a 'basal' adjuvant ( Fig. 4) because we expected the additional adjuvant effect from the flagellin which could enhance the antigenicity of the S0 over the basal Freund's adjuvant effect.