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

As flagellin has shown enormous potency as an adjuvant through TLR5 on a number of innate and adaptive immune cells [19] , we evaluated the ability of each recombinant protein to activate TLR5 to interpret different S0-specific IgG outcomes among various flagellin adjuvanted groups. As shown in Fig. 5 , flagellin, regardless of whether it was conjugated to S0, activated the TLR5 pathway. In particular, F alone activated this pathway to significantly higher levels than the levels achieved by S0-F or F-S0 based on the 1 nM treatment data. This activation tendency was also confirmed in vivo (Fig. 6A) . The superior ability of F-S0 to induce S0-specific IgG relative to the mixture of S0/F may result from the effects of the conjugation. In fact, the conjugation of immunopotentiators to antigens has been demonstrated to elicit stronger immune responses than nonconjugated, separated treatments in many previous research investigations [14, [30] [31] [32] . This stronger response occurs because conjugation ensures the delivery and uptake of both antigen and immunopotentiator by the same antigen presenting cell, assuring the potentiation of antigen-specific immune responses [33] [34] [35] . Indeed, the conjugation of flagellin to various antigens has been shown to provide stronger antigen-specific humoral immune responses than separated mixtures [14, 32, 36] .