Molecular basis of the variation exhibited by avian infectious bronchitis coronavirus (IBV)

IBV serotype-specific, virus neutralising (VN) antibody is induced by the S1 subunit of the spike (S) glycoprotein. A Portuguese isolate (Port/322/85) is considered to be an in vivo recombinant. VN tests showed that it belongs to the Massachussetts (Mass) serotype. Correspondingly, the sequence of S1 and S2 was extremely similar to that of older Mass isolates. However, the matrix (M) glycoprotein and upstream gene sequences were atypical of these Mass strains and more closely resembled other serotypes isolated in Europe. The recombination event had occurred within the sequence between the M and S genes (corresponding to mRNA 3) or near the 3' terminus of the S2 gene.