Virological, immunochemical, and cytochemical studies of four HeLa cell lines infected with two strains of influenza virus.

The production of infectious virus, hemagglutinin, and viral (V) antigens and the changes in ribonucleoprotein (RNP) and lipoprotein metabolism have been studied in four sublines of HeLa cells infected with the PR8 and a PR8 recombinant strain of influenza virus. Much greater amounts of infectious virus and much less hemagglutinin were produced by the PR8 recombinant than by PR8 virus in all four cell lines. Different amounts of infectious virus per infected cell were produced by the recombinant in the four cell lines, whereas very little infectious virus was produced by the PR8 strain in any of the HeLa cells. In all cell lines infected with both strains of virus, "soluble" (S) antigen appeared early in the nucleolus. In cells infected with PR8 recombinant, S antigen subsequently filled the nucleus and later appeared in the cytoplasm. In most cells infected with PR8 virus, nuclear S antigen did not fuse to fill the nucleus, and S antigen was not detected in the cytoplasm. V antigen was observed in the cytoplasm of cells when diffuse nuclear S antigen had formed. The earliest and most frequent change in the RNP of the infected cells was a decrease in stainable RNP spherules (nucleolini) in the nucleolus. This was followed, in a smaller proportion of cells, by the appearance of nuclear and cytoplasmic inclusions containing RNP. There was a characteristic difference in the morphology of the cytoplasmic inclusions produced by the two strains of virus, but the same types of inclusions were observed in all four HeLa lines. A significant increase in lipoprotein was observed only in association with the cytoplasmic inclusions produced by PR8 recombinant virus. There was a striking difference in the proportion of cells with cytochemical changes in RNP in the four cell lines. A significant cytopathic effect (CPE) was observed only in three virus-cell systems in which a high proportion of cells exhibited changes in nucleolinar RNP. It is suggested that disappearance of RNP in the nucleolini may be an indication of shutdown of host ribonucleic acid synthesis and that this in turn results in a CPE. Virus infection resulted in a C-mitotic block that was followed by karyorrhexis. Infection of the cell did not always result in the production of infectious virus, in changes in the RNP of the nucleolini, in the development of nuclear or cytoplasmic RNP inclusions, or in CPE. The results suggest that production of infectious virus, shutdown of cellular RNP synthesis with accompanying CPE, and the formation of inclusions appear to be independent events.