Immunoglobulins in human serum reactive with murine Friend leukaemia virus

Fresh human sera neutralize Friend leukaemia virus (FLV). The activity is abolished by heating (56 degrees C for 30 min), hydrazine and EDTA treatment, suggesting the involvement of complement. Human sera also contain antibody which specifically reacts with FLV. Following incubation with human whole serum, IgG and F(ab')2 fragments, FLV acquire the ability to bind anti-human Ig sera, as shown in neutralization and radioimmunoprecipitation assay. The same is true for FLV-infected cells but not for uninfected control cells, as assessed by immunofluorescence. The binding of antibody to FLV-infected cells is prevented by pre-treating the cells with antisera to FLV and FLV-gp71, and is completed by FLV, FLV-gp71 and, to a lesser extent, by FLV-p12 and p30.