Surface expression of a nonstructural antigen on influenza A virus-infected cells.

Rabbit antiserum to the influenza A virus nonstructural protein, NS1, was used for indirect immunofluorescence studies of infected cells. Nonstructural antigens were detected on surfaces of P815 cells as early as 4 h after infection with A/WSN/40 virus. Adsorption of the serum with virion structural proteins did not affect the observed fluorescence, and a progressive increase in surface fluorescence at later times postinfection indicated that the surface antigen was newly synthesized during the replication cycle.