Abstract
Avian infectious bronchitis virus (IBV) is the causative agent of infectious bronchitis, which results in considerable economic losses. It is imperative to develop safe and efficient candidate vaccines to control IBV infection. In the current study, recombinant baculoviruses co-expressing the S1 and N proteins and mono-expressing S1 or N proteins of the GX-YL5 strain of IBV were constructed and prepared into subunit vaccines rHBM-S1-N, rHBM-S1 and rHBM-N. The levels of immune protection of these subunit vaccines were evaluated by inoculating specific pathogen-free (SPF) chickens at 14 days of age, giving them a booster with the same dose 14 days later and challenging them with a virulent GX-YL5 strain of IBV 14 days post-booster (dpb). The commercial vaccine strain H120 was used as a control. The IBV-specific antibody levels, as well as the percentages of CD4+ and CD8+ T lymphocytes, were detected within 28 days post-vaccination (dpv). The morbidity, mortality and re-isolation of the virus from the tracheas and kidneys of challenged birds were evaluated at five days post-challenge (dpc). The results showed that the IBV-specific antibody levels and the percentages of CD4+ and CD8+ T lymphocytes were higher in the rHBM-S1-N vaccinated birds compared to birds vaccinated with the rHBM-S1 and rHBM-N vaccines. At 5 dpc, the mortality, morbidity and virus re-isolation rate of the birds vaccinated with the rHBM-S1-N vaccine were slightly higher than those vaccinated with the H120 control vaccine but were lower than those vaccinated with the rHBM-S1 and rHBM-N vaccines. The present study demonstrated that the protection of the recombinant baculovirus co-expressing S1 and N proteins was better than that of recombinant baculoviruses mono-expressing the S1 or N protein. Thus, the recombinant baculovirus co-expressing S1 and N proteins could serve as a potential IBV vaccine and this demonstrates that the bivalent subunit vaccine including the S1 and N proteins might be a strategy for the development of an IBV subunit vaccine.
Highlights
Avian infectious bronchitis (IB) is a highly contagious disease of chickens caused by the infectious bronchitis virus (IBV), belonging to the Gammacoronavirus genus within the Coronaviridae family [1]
The results of PCR identification showed that the recombinant bacmids rHBM-S1, rHBM-N and rHBM-S1-N were generated (Figure S2)
The purified recombinant bacmids rHBM-S1, rHBM-N and rHBM-S1-N were transfected into Sf9 insect cells to obtain the recombinant baculovirus
Summary
Avian infectious bronchitis (IB) is a highly contagious disease of chickens caused by the infectious bronchitis virus (IBV), belonging to the Gammacoronavirus genus within the Coronaviridae family [1].IBV affects chickens of all ages and types and primarily infects the respiratory and urogenital systems of chickens, causing massive economic losses [2,3,4]. Viruses 2018, 10, 347 serotypes of IBVs or circulating variant viruses, frequently leading to immune failures and making it extremely difficult to control the disease [5,6,7]. Control of the disease currently relies on conventional live-attenuated and inactivated vaccines [8,9,10]. Inactivated vaccines are high in cost and do not establish long-term immunity. The application of inactivated vaccines alone has frequently failed to induce strong cellular immunity, resulting in little or no protection [14,15]. Despite the widespread application of these conventional vaccines, IB continues to cause severe economic losses in many countries, underscoring the need to develop new safer and more effective candidate vaccines for the practical control of IBV
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