Avian Coronavirus Spike Proteins as Tools to Elucidate the Molecular Determinants of IBV-Host Interactions.

Attachment of a virus to the host cell is the first step in determining cell, tissue and host specificity. While the host tropism of the avian coronavirus infectious bronchitis virus (IBV) is restricted to chickens, tissue tropism and pathogenicity varies widely between different IBV strains. The molecular determinants causing these differences are, however, unknown. Here we investigated the binding characteristics of the viral attachment protein spike (S) of IBV strains with different pathogenicity to host tissues and glycans. To this end, recombinant soluble spike proteins were produced in a mammalian expression system and spike histochemistry was performed on chicken tissues. Our data showed that the S1 protein of the virulent IBV-M41 specifically bound to cilia and goblet cells of the chicken respiratory tract, in an alpha2,3-linked sialic acid dependent manner. Furthermore, glycan array revealed that M41-S1 binds with high specificity, but low avidity, to one particular alpha 2,3-linked disialoside. In contrast, IBV-S1 from the vaccine strain H120 or from the non-virulent, cell culture adapted strain Beaudette had reduced or no binding to chicken tissues, respectively, in agreement with the reduced abilities of these viruses to replicate in vivo. In conclusion, our recombinant spike proteins are excellent tools further dissect the molecular determinants of IBV-host interactions, but are also extremely useful in studying the tissue and host tropism of IBV and that of other avian coronaviruses.