IDENTIFICATION OF A VARIANT SUBGROUP A STRAIN OF RESPIRATORY SYNCYTIAL VIRUS

During epidemiologic surveillance of children with respiratory syncyti al virus (RSV) disease in Huntington, W.Va., we identified seven strai ns of a new variant subgroup A RSV (subgroup A-Var) by their reactions in an enzyme immunoassay with two anti-F monoclonal antibodies (MAbs) specific for two epitopes, Fl and F4, generated against the subgroup B RSV, The prototype strain of subgroup A and all other subgroup A fie ld strains from that epidemiologic year failed to react with these two subgroup B MAbs, Additional enzyme immunoassays with 18 subgroup B an ti-F MAbs specific for 14 epitopes showed that subgroup A-Var strains also reacted with a MAb specific for the subgroup B FZ epitope, In a r adioimmune precipitation assay, the molecular size of the subgroup A-V ar F2 subunit of the fusion (F) protein clearly differed from those of both prototype strains of subgroup A and subgroup B RSV, The molecula r size of the F2 subunit of subgroup A-Var (24 kDa) was intermediate b etween the size of the F2 subunit of subgroup A (25 kDa) and that of s ubgroup B (23 kDa), However, the molecular sizes of the F1 subunits of both subgroup A and subgroup A-Var were identical (54 kDa) and slight ly larger than those of the F1 subunits of both subgroups B1 and BZ (5 3 kDa), These data suggest that subgroup A-Var may represent a distinc t RSV A subgroup, analogous to subgroup BI and B2 RSV, and it is the f irst-identified naturally occurring subgroup A RSV with an F protein d ifferent from that of the prototype A RSV.