Age related IgG subclass response to respiratory syncytial virus fusion protein in infected infants.

Respiratory syncytial virus (RSV) fusion protein was purified by immunoaffinity chromatography using a mouse monoclonal antibody coupled to Affi-gel 10. The fusion protein was homogeneous by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and free of other detectable viral or cellular protein. The purified fusion protein was used in a quantitative enzyme-linked immunosorbent assay (ELISA) to measure the age-related antibody response to this protein in infected infants. The four IgG subclasses, IgA and IgM levels were determined for infants under 6 months of age, infants aged 6 months to 1 year and infants aged 1 year and over. Most infants over 6 months of age showed marked increases in both IgG1 and IgG3 antibodies with poor or negligible response with IgG2 and IgG4. By contrast infants under 6 months failed to respond by the production of IgG antibodies, although increases in IgA and IgM levels were observed. These data may explain the failure of primary RSV infections to induce protective immunity and have implications for the strategic use of attenuated RSV vaccines.