The Comparision Of Immune Protection Conferred By Three Commonly-Used Commercial Attenuated Vaccines Against Guangxi Prevalent Isolates Of IBV

Avian infectious bronchitis (IB) is an important contagious disease of chickens and causes serious losses to poultry industries worldwide. Vaccination is the important measure for the prevention and control of IB at present. H120 attenuated vaccine was the most commonly-used vaccine in the chicken farms, and the application of 4/91 and LDT3-A attenuated vaccine showed a increasing trend in recent years. Previous studies showed that the most IBV isolates of Guangxi occurred mutation and their serotypes were different from those of the current vaccine strains. In order to understand the immune protection conferred by the commonly-used commercial IBV attenuated vaccines against the IBV prevalent isolates in Guangxi, and provide the reference for choosing the suitable vaccines to prevent and control IB, the representative IBV isolates GX-YL5, GX-GL11079 of predominant serotype Ⅰ, Ⅱ in Guangxi, and the GX-NN09032 isolate with the same serotype Ⅴ as 4/91 vaccine were selected to evaluate and compare the immune protection conferred by the commonly-used commercial IBV attenuated vaccines of H120, 4/91 and LDT3-A.The 7 days old SPF chicks were vaccinated oculonasally by H120,4/91 and LDT3-A attenuated vaccines with the recommended doses. The IBV specificity antibody levels and the percentages of the CD4+, CD8+T lymphocytes in the peripheral blood were detected by the indirect ELISA and the flow cytometry test, respectively; the mRNA transcription levels of IL-1β, IL-6, IL-12 in the peripheral blood were detected by the real-time fluorescent quantitative PCR at 0,1,23 weeks post inoculation(PI).3 weeks PI, the chicks were challenged with the Guangxi representative isolates GX-YL5, GX-GL11079 and GX-NN09032. The morbidities, mortalities, clinical symptoms and autopsy lesions of infected chicks were recorded daily for 21 days to calculate the infection rate and protection rate. The IBV loads of the tracheal washes and kidney tissue chickens as well as the mRNA transcription levels of the IL-1β, IL-6, IL-12 in the tracheal washes at 5,14,21 days post infection were detected by the real-time fluorescent quantitative PCR.The ELISA results showed that the antibody of each vaccinated group was produced at one week PI. The antibody levels in H120 and 4/91 vaccinated groups reached the peak at 2 weeks PI, and the antibody levels in LDT3-A vaccinated groups kept rising at 3 weeks PI. IBV specific antibody in each vaccinated groups showed highly significant difference (P<0.01) or significant difference (P<0.05) compared with the non-vaccinated group within 3 weeks PI. The IBV specific antibody levels of LDT3-A vaccinated group were significantly (P<0.05) higher than those of H120 and 4/91 vaccinated groups. The antibody levels of the H120 vaccinated group were slightly higher than the 4/91 vaccinated group, but the difference between them wasn’t significant (P>0.05).The flow cytometry results indicated that the percentages of CD4+, CD8+T lymphocytes in vaccinated groups showed the rising trend with different degrees, and were significantly (P<0.05) or highly significantly (P<0.01) higher than those in the non-vaccinated group. The percentages of CD4+, CD8+T lymphocytes of the 4/91 vaccinated group were higher (P<0.05) than those of the LDT3-A vaccinated group and the LDT3-A vaccinated group was same as the H120 vaccinated group.The results of the real-time fluorescent quantitative PCR showed that the mRNA transcription levels of IL-1β, IL-6, IL-12 in the peripheral blood of vaccinated groups up-regulated with different degrees compared to the non-vaccinated group within 3 weeks PI. The 4/91 vaccinated group had the highest mRNA transcription levels of IL-1β, IL-6, IL-12. The mRNA transcription levels of IL-1β, IL-6, IL-12 in the H120 vaccinated group were lower than those in the 4/91 vaccinated group but were higher than the LDT3-A vaccinated group.The vaccinated-challenge test results showed that the protection rates of 4/91, LDT3-A and H120 vaccine against the infection of three IBV representative isolates of Guangxi were 75%-83.7%,66.7%-75%, and 41.7%-58.3%, respectively. The viral loads in tracheal washes and kidney tissues of three vaccinated groups were lower significantly (P<0.05) or highly significantly lower (P<0.01) than the non-vaccinated challenge group. The viral loads of 4/91 vaccinated group were lowest, and those of LDT3-A vaccinated were lower, but the H120 vaccinated group were highest. On the other hand, the immune protective efficacy of H120 attenuated vaccine with serotype Ⅲ against the Guangxi isolates of GX-YL5, GX-GL11079 and GX-NN09032 with serotype Ⅰ, Ⅱ and V, respectively were poor. The 4/91 attenuated vaccine provided better protection against the IBV isolates with the same serotype than those with different serotypes.The IL-1β, IL-6 and IL-12 mRNA transcription levels in the tracheal washes of vaccinated groups up-regulated with different degrees at 5,14 days post infection and were higher than those in the non-vaccinated challenged groups, indicating that cytokines secreted by trachea mucosa increased and they played an important role in immunoregulation.In conclusion, the present study showed that the H120,4/91 and LDT3-A attenuated vaccines could stimulate effectively the immunized chickens to produce different levels of humoral immune response and cellular immunity to resist and eliminate the IBV infection, and they could stimulate cytokines secreted, which played a role in regulating of the immune response.4/91 attenuated vaccine had the best clinical protection and virus inhibition effect for the IBV prevalent isolates of Guangxi. The clinical protection and virus inhibition effect of LDT3-A attenuated vaccine was a little lower than those of 4/91 attenuated vaccine, but H120 attenuated vaccine’s clinical protection and virus inhibition effect was poor. The immune protection conferred by 4/91 attenuated vaccine against the GX-NN09032 prevalent isolate with the same serotype was superior to those isolates with different serotypes.