Spike protein derived from an apathogenic IBV strain confers attenuated phenotype to a nephropathogenic IBV strain

Abstract

Infectious bronchitis virus (IBV), aGammacoronavirus, causes the economically damaging disease of poultry, infectious bronchitis. Development of IBV live attenuated vaccines (LAVs) is dependent on the supply of embryonated hens’ eggs and attenuation through serial passaging, upwards of 80 times. Vaccine development needs to keep pace with IBV evolution; an issue compounded as cross protection between individual IBV serotypes is unpredictable and often limited. Rational attenuation alongside the ability to propagate LAVs in cell culture offers significant advantages in terms of adaptability, cost, and speed. Most field IBV strains exhibit restrictedin vitrotropism, being unable to replicate in primary or continuous cells without serial passage and adaptation. Beaudette, an attenuated IBV strain, is capable of replication in Vero cells, an ability conferred by the spike (S) glycoprotein. In this study, utilizing a recombinant IBV based on the nephropathogenic IBV strain D388, in which the S sequence is replaced with the equivalent sequence derived from Beaudette, we determine that the Beaudette spike can confer the ability to replicate in Vero cells and Beaudette’s associated attenuatedin vivophenotype to a distantly related IBV strain. Assessment of infectious progeny and viral RNAin vivosuggests that attenuation was conferred by a tissue tropism-independent molecular mechanism. Analysis of innate immune responses revealed a lower intensity and less inflammatory profile. Our findings support the use of the Beaudette S protein as an avenue for the development of rationally attenuated, cell culture-propagated rIBV vaccines and identify the S protein as a contributor to nephropathogenicity.