Evaluation of a solid-phase immunoassay with fluorescein isothiocyanate-conjugated heterogeneous or monoclonal antibodies for identification of virus isolates, with influenza virus as a model

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Abstract
A solid-phase immunofluorometric assay was evaluated for the identification of viruses isolated in tissue culture, with influenza virus as a model. Purified IgG from hyperimmune rabbit sera specific for contemporary strains of influenza A or B was covalently attached to microscopic plastic beads to capture virus. Fluorescein isothiocyanate (FITC)-conjugated antibodies of different specificities were then reacted with bound antigen; the resulting complexes were quantified in a suitable filter fluorometer. The assay, with appropriately absorbed FITC-conjugated 2nd antibody, reliably identified virus present in harvests from cell cultures infected with clinical specimens. For influenza A (H1N1) virus, sensitivity of detecting antigen was about 8- to 32-fold less when an FITC-conjugated monoclonal IgG antibody pool specific for epitopes in 3 different antigenic sites on influenza hemagglutinin was used as the 2nd antibody, as compared to when IgG from hyperimmune sera specific for virus or its components was used as the 2nd antibody. The immunofluorometric assay provides a method for quantitative detection of viral antigen in tissue culture fluids and objective identification of virus type and subtype with FITC-conjugated reagents.