PRIMARY INFLUENZA-A VIRUS-INFECTION INDUCES CROSS-REACTIVE ANTIBODIESTHAT ENHANCE UPTAKE OF VIRUS INTO FC RECEPTOR-BEARING CELLS

Sera of young children who had had a primary infection with influenza A virus or were immunized with a live attenuated influenza A virus vac cine were examined for antibody responses that neutralized virus or en hanced uptake of virus into Fc receptor-bearing cells, because antibod ies that enhance uptake of influenza virus into Fc receptor-bearing ce lls have been reported using mouse immune serum and monoclonal antibod ies. The neutralizing antibody titers to the homologous infecting viru s and to another H1N1 virus isolated several years later were higher a fter natural infection than after infection with the live attenuated v irus. Natural infection and the attenuated vaccine induced antibodies that enhanced uptake of homologous virus and H1N1 virus isolated sever al years later. These results demonstrate that primary influenza A vir us infection results in the induction of infection-enhancing antibodie s.