Sequence conservation in the attachment glycoprotein and antigenic diversity among bovine respiratory syncytial virus isolates.

Partial nucleotide sequences were determined from the coding regions of the attachment glycoprotein (G) mRNAS of eight isolates of bovine respiratory syncytial virus (BRSV). The antigenic characteristics of 18 field and reference isolates were analyzed using the reactivity patterns of monoclonal antibodies (MAbs) directed against the human respiratory syncytial virus (HRSV) and BRSV G. fusion protein (F), nucleoprotein (N), and phosphoprotein (P), by radioimmunoprecipitation and immunofluorescence assays. The MAb reaction patterns demonstrated some random antigenic differences among the isolates, but for the most part were cross-reactive to the viral protein epitopes, especially on the F protein. Structural differences in the F and P proteins were observed among BRSV isolates; the P protein migrated at three different apparent molecular weights on PAGE gels. Antigenic and structural variation occurs among isolates, however, the structural differences in the P protein did not correlate with the antigenic differences among the F, N and P proteins. The G mRNA nucleotide sequence identities were high, ranging from 94.1 to 99.9%, and the predicted amino acid sequence identities ranged from 89.9 to 99.6%. Variance was due to substitution point mutations. The G protein ectodomains contained areas of sequence divergence flanking a highly conserved region, with four cysteine residues, which is analogous to the putative HRSV receptor binding domain. The high sequence and amino acid identities and random antigenic diversity among the isolates indicates that the BRSV isolates analyzed belong in a monophyletic group.