Early events in myxovirus replication: immunofluorescent spots.

Indirect immunofluorescent staining of Ehrlich ascites tumor cells infected with two influenza A strains, WSA (HON1) and TUR (Hav1 Nav3), revealed early fluorescent spots which became detectable in the cytoplasm within 30 minutes of infection, before the nucleoprotein antigen appeared in the nucleus. These spots seemed to be linked to some structural antigen of the virus not identical with hemagglutinin, neuraminidase, or nucleoprotein. Their formation was not inhibited by actinomycin, p-fluorophenylalanine or amantadine in concentrations sufficient to block viral replication; amantadine led to an altered time course of spot evolution and to the emergence of coarser spots. The exact serologic specificity of early spots remains to be worked out but appears to differ from that of known influenza A antigens.