Host-dependent restriction of influenza virus maturation

Abstract

Host-dependent restriction of influenza virus replication in nonpermissive HeLa cells was studied under single cycle conditions using as inoculum bovine kidney (MDBK)-grown virus which was relatively free of defective interfering particles. Biochemical and ultrastructural changes in infected HeLa cells were compared to MDBK cells, which are permissive for influenza virus replication [ Choppin and Pons (1970), Virology, 42, 603–610]. Two subclasses of virus-specific nucleoproteins separated in renografin density gradients were present in the nucleus and cytoplasm of both MDBK and HeLa cells; however, the assembly of the 1.26 g/ml virus-specific RNPs occurred at a faster rate in HeLa cells than in MDBK cells. The overall patterns of synthesis of polypeptides in HeLa cells were similar to those seen in MDBK cells, and the polypeptide compositions of virus released from HeLa and MDBK cells were also similar. Electron microscopy showed that elongated virus particles accumulated in tightly packed arrays on the plasma membrane of HeLa cells; however, only a small number of spherical virions were observed budding from the plasma membrane of MDBK cells. Large, intracytoplasmic vesicles filled with budding virus particles were numerous in HeLa cells but were not observed in MDBK cells. Many finely striated inclusions and dense granular inclusions were observed in the cytoplasm of HeLa cells within 24 hr after infection. In contrast, MDBK cells showed much less cytopathic effect at 24 hr after infection, and virus-induced inclusions occurred much less frequently than in HeLa cells. These results suggest that. in HeLa cells the final stages of maturation of virus particles at the plasma membrane may be,blocked, allowing the accumulation of viral products within the cytoplasm and budding virus particles on. the surface of nonpermissive cells. Thus, in the absence of defective interfering particles in the inoculum, the host-dependent restriction in influenza virus replication in HeLa cells does not occur early in the virus growth cycle, but appears to be due to a defect in a late event involving the participation of the plasma membrane. in virus maturation.