Analysis of the binding of monoclonal and polyclonal antibodies to the glycoproteins of antigenic variants of human respiratory syncytial virus by surface plasmon resonance

The surface glycoproteins of human respiratory syncytial virus (hRSV), F and G, are the major protective antigens of the virus. Both are antigenically variable, although to different degrees, but the role of antigenic variation in the pathogenesis of hRSV disease has not been fully evaluated. Assessment of immunity to different virus strains is difficult with conventional antibody assays where differing properties of the virus antigens, other than antigenicity, may influence the outcome of the assay. Here, we have developed BIAcore™ surface plasmon resonance based assays for antibodies to the glycoproteins of hRSV which allow valid comparison of antibody titres against multiple hRSV strains. Glycoproteins from a number of lineages of hRSV sub-group A were captured from lysates of infected cells onto the dextran coated surface of a BIAcore™ sensor chip via primary monoclonal antibodies (MAbs) to conserved epitopes. For the G glycoprotein, primary MAbs were conjugated directly to the dextran of the sensor chip via free amide groups. For the F glycoprotein, direct conjugation was found to inactivate the MAb and primary MAb was immobilised on the chip via rabbit anti-mouse Fc antibody fragments in an indirect system. Using monoclonal antibodies as secondary MAbs, the glycoproteins in both systems were shown to exhibit a sub-set of conserved and variable epitopes, with some epitopes of both sorts being unavailable, presumably blocked by the primary antibody. Polyclonal anti-hRSV sera raised against viruses of different genotype bound equally to both F and G glycoproteins from homologous and heterologous viruses suggesting that mice immunised systemically with lysates of cells infected with recent isolates of virus do not respond well to genotype specific epitopes.