Production and immunogenicity of chimeric virus-like particles containing the spike glycoprotein of infectious bronchitis virus

Lv, Lishan; Li, Xiaoming; Liu, Genmei; Li, Ran; Liu, Qiliang; Shen, Huifang; Wang, Wei; Xue, Chunyi; Cao, Yongchang

Mouse serum samples were immunized with chimeric VLPs and inactivated IBV H120 viruses (diluted 400 times) and then analyzed for their S1-specific IgG antibodies by ELISA. Purified S1 protein was selected for the ELISA experiments because S1 protein was a common surface antigen between chimeric VLPs and H120 viruses; therefore, measurement of S1-specific IgG antibodies should make the results from both groups more comparable. In addition, since there were no available standard antigens, the quantification of S1-specific antibodies was difficult; accordingly, the OD was used for comparison. In both groups, each boost increased S1-specific antibody responses. Additionally, chimeric Fig. 7 . IBV-specific neutralization antibody titers in immunized SPF chickens. Serum samples from SPF chickens were collected on the 28th day post immunization. 100× TCID50 IBV H120 was mixed with serial diluted sera, after which the mixtures were inoculated into 9-day-old SPF embryonated chicken eggs. The neutralization titer was then expressed as the reciprocal of the highest serum dilution that exhibited neutralization in 50% of the eggs. Fig. 6 . Serum S1-specific IgG antibodies. Ten-day-old SPF chickens were intramuscularly immunized twice at 2-week intervals with chimeric VLPs, H120 or PBS. Sera were tested for S1-specific IgG antibodies by ELISA. Pre-immune sera from SPF chickens had no detectable S1-specific antibodies. Optical densities were read at 450 nm. Bars represent the arithmetic mean antibody titers ± SE. VLPs induced higher S1-specific antibody responses than inactivated IBV H120 viruses (p ＜ 0.01) after the first boost (Fig. 3) .