Coronavirus IBV: relationships among recent European isolates studied by limited proteolysis of the virion glycopolypeptides.
After the year 1978, strains of avian infectious bronchitis virus (IBV) were isolated in the Netherlands and the UK which were assigned by neutralisation tests to four new serotypes (arbitrarily designated A, B, C and D in this communication) distinct from the long recognised US serotypes. We have labelled, with 35S-methionine, the structural polypeptides of 12 of the European isolates during growth in de-embryonated eggs. The S2, spike-anchoring, polypeptide of isolates of all four serotypes had a molecular weight of 87 000 (87K) whereas the US IBV-M41 strain had S2 of 84K. When the isolates were grouped according to the molecular weight of the other spike glycopolypeptide, S1, and the membrane (M) glycopolypeptide four groups emerged which corresponded to the serotypes based on neutralisation tests. Serotypes A (isolates D207, 1, 5 and 6) and B (isolates 7, 8 and D3896) had S1 of 91.5K while serotypes C (isolates 9 and D3128) and D (isolates D212 and D1466) had S1 of 90K. The M of serotypes A and D had a molecular weight of 30K while that of serotypes B and C was 27K. Chymotrypsin and protease V8 were used for limited proteolysis, the hydrolysis of S1 giving the greatest discrimination between serotypes. After proteolysis of S1 the UK isolates of serotype A gave identical profiles which were very similar to the Dutch serotype A isolate D207. Isolates of serotype B gave S1 profiles very similar to those of serotype A, as did D274 which is serologically related to both groups A and B. Serotypes C and D were distinguishable from each other and from serotypes A and B on the basis of the S1 peptide profiles. These results strengthen the view that the UK and Dutch isolates are closely related and that serotypes A and B are more closely related to each other than to either group C or D serotypes.