Expression of influenza A virus internal antigens on the surface of infected P815 cells

A panel of hybridoma antibodies was used to study the expression of the 2 major internal influenza A virus proteins, matrix protein (M), and nucleoprotein (NP) on the surface of influenza A-infected P815 cells. Using a sensitive radioimmunoassay (RIA) performed with live infected P815 cells only minute amounts of M were detectable, whereas M was not detected in 3 other cell-surface assays. In contrast, NP was detected in 10-fold greater amounts than M and 10- to 50-fold lower amounts than the viral glycoproteins by RIA. Furthermore, the presence of NP could be demonstrated by immunofluorescence, microcytotoxicity, and agglutination assays performed on live infected cells.