Protection of chickens against infectious bronchitis virus with a multivalent DNA vaccine and boosting with an inactivated vaccine

Yan, Fang; Zhao, Yujun; Hu, Yongting; Qiu, Jianyang; Lei, Wenxin; Ji, Wenhui; Li, Xuying; Wu, Qian; Shi, Xiumin; Li, Zhong

The concentrations of serum anti-IBV antibodies were measured with a serum-neutralizing assay and an ELISA. Mean serum IBV-neutralizing antibody titers of the different groups immunized with different vaccines as shown in Fig. 1 . Values are expressed as the log 10 inverse mean titer ± SD for 10 chickens in each group. Different letters above the columns indicate significant differences (p ＜ 0.01) while identical letters indicate that there was no significant difference (p ＞ 0.05) within each time point. The titers measured at each time point were significantly different in each group (p ＜ 0.01). As expected, sera from the pre-primed chickens and birds immunized with the pVAX1 vector had no detectable levels of antibodies against IBV according to the serum-neutralizing assay (Fig. 1) . Antibody titers for chickens immunized with pVAX1-16S1, pVAX1-16M, pVAX1-16N, or pVAX1-16S1/M/N increased from day 7 to day 49 (Fig. 1) . Antibody titers of the multivalent pVAX1-16S1/M/N-immunized chickens were significantly higher than those of all chickens immunized with the monovalent DNA vaccine on days 21, 35, and 49 (p ＜ 0.01). These results indicate that the triple-gene plasmid mix induced a greater antibody response than the single-gene plasmid. Antibody titers of the pVAX1-16S1/M/N + inactive vaccine group were much higher than those of the pVAX1-16S1/M/N group (p ＜ 0.01) on days 21 and 35. However, no significant difference (p > 0.05) in antibody titers between the two groups was observed on day 49. These findings were also confirmed with an ELISA assay as shown in Fig. 2 . Data are expressed as the mean ± SD for 10 chickens in each group. Different letters above the columns indicate significant differences (p ＜ 0.01) while DNA vaccine and an inactivated vaccine 57 Fig. 3 . Lymphocyte proliferation rates of chickens from the different groups administered different vaccines. Data are expressed as the mean OD570 values ± SD (n = 5). Columns are labeled with letters. Different letters indicate statistically significant differences (p ＜ 0.01) between different treatments within the time point while columns with the same letters indicate that no significantly differences (p ＞ 0.05) were observed. Absence of a letter indicates that there were no significant differences (p ＞ 0.05) between any of the time points. Although not indicated in the graph, the differences between corresponding treatments from different day groups are significant (p ＜ 0.01).