Fluorescent Antibodies to Influenza Virus in Various Immunoglobulin Fractions of Serum after Natural Infection or Vaccination

Abstract

Abstract Sera from confirmed cases of influenza and from recipients of attenuated or killed influenza virus vaccines were tested for IgM, IgA, and IgG antibodies by the indirect fluorescent antibody technique. Treatment with 2-mercaptoethanol and by sucrose density gradient centrifugation proved that IgM antibodies, as well as IgA and IgG, were located exclusively in the 7S fraction of globulin. The 7S IgM antibodies rose rapidly after onset of disease in all cases and persisted in decreasing titers for 3 months. The appearance of IgA antibodies was detected in 75% of the cases. These attained lower titers and were of shorter duration. IgG fluorescent antibody (FA) titers increased in all subjects and the levels observed were closely analogous to hemagglutination inhibition titers. The three classes of FA were proven to be independently located in their respective subunits of immunoglobulin and to be specific for either type A or B influenza virus. IgM antibody increases were measurable in 52% of the vaccinees receiving attenuated viruses administered intranasally but only 12% responded with IgA antibodies. Both classes of antibody were of lower titer and shorter duration than were those after clinical disease. Their development, titer, and decline were independent of the presence or absence of IgG antibodies. In fact, many subjects had IgG antibodies at the time of vaccination. IgM and IgA antibodies in low titers were detected in 57% of the post-inoculation specimens from persons receiving inactivated vaccine. All had responded with increased titers of antibody in the IgG fraction. Finally, it was shown that it is possible to detect recent influenza infection or vaccination by the demonstration of IgM or IgA antibodies in serum.