Antigenic and molecular analyses of the variability of bovine respiratory syncytial virus G glycoprotein.

Antigenic variation among eight bovine respiratory syncytial virus (BRSV) isolates was determined using monoclonal antibodies (MAbs) specific for the attachment (G) protein. Two major (and one intermediate) subgroups were identified, as well as one strain that did not fit any pattern. The subgroups could also be differentiated on the basis of the Mr of the F protein cleavage product, F2. The nucleotide sequence of the G gene of seven of the BRSV strains was determined and compared with published G gene sequences. Subgroups A and A/B were more closely related in protein sequence than subgroups A and B or subgroups A/B and B. These results could not be correlated with those obtained by the determination of the Mr of the F2 polypeptide. Multiple sequence alignments showed a high level of amino acid identity at the inter-subgroup level (85% identity between subgroup A and subgroup B strains), similar to the intra-subgroup human (H)RSV identity, suggesting that the BRSV isolates form a continuum rather than distinct subgroups. However, unusual variability was observed within the immunodominant domain (amino acids 174-188) in contrast with the situation in HRSV strains belonging to the same subgroup.