Nanoparticle orientationally displayed antigen epitopes improve neutralizing antibody level in a model of porcine circovirus type 2

Ding, Peiyang; Zhang, Teng; Li, Yafei; Teng, Man; Sun, Yaning; Liu, Xiao; Chai, Shujun; Zhou, Enmin; Jin, Qianyue; Zhang, Gaiping

High levels of PCV2-specific antibodies and low levels of Cap (169-180)-specific antibody may help improve NA titers. 27 NA titer was significantly improved after AuNPs were added ( Figure 6D ). On comparing the significant changes of Cap-specific antibodies with PCV2-specific antibodies and NA in the Carbopol and Freund's adjuvant groups, we found that AuNPs significantly enhanced NA, rather than Cap-specific antibodies. These data indicated that AuNPs enhanced NAs mainly due to reasonable display of neutralizing epitopes and masking of the immunodominant epitope. effect of lyophilization on the immune response As shown in Figure 7A , the Cap-specific antibody levels in non-lyophilized group was higher than in the lyophilized group (P=0.15), which may, in part, be due to the inactivation of a portion of Cap protein during lyophilization process. Interestingly, PCV2-specific and NA levels in lyophilized group were markedly higher than in non-lyophilized group ( Figure 7B and D) . The ratio of IgG against Cap (169-180)/ IgG against PCV2 in lyophilized group was obviously lower than in non-lyophilized group ( Figure 7C ). These data suggested that the slight reduction of Cap-specific antibody did not affect NA and the stability of Cap-AuNPs conjugation was likely enhanced following lyophilization. Cap protein spatial orientation is more stable, thus offering an advantage in transportation and long-term preservation. 41 Furthermore, these data confirmed that AuNPs promoted NA mainly due to the reasonable display of neutralizing epitopes.