Subacute sclerosing panencephalitis virus dominantly interferes with replication of wild-type measles virus in a mixed infection: implication for viral persistence.

Interaction between the Edmonston or Nagahata strain of acute measles virus (MV) and the defective Biken strain of MV isolated from a patient with subacute sclerosing panencephalitis (SSPE) was examined by a cell fusion protocol. Biken-CV-1 cells nonproductively infected with Biken strain SSPE virus were fused with neomycin-resistant CV-1 cells. All the fused cells selected with the neomycin analog G418 expressed Biken viral proteins, as determined by an immunofluorescence assay. This procedure enabled the transfer of Biken viral genomes into cells previously infected with MV. In the fused cells coinfected by Biken strain SSPE virus and Edmonston or Nagahata strain MV, early MV gene expression was suppressed, as determined by immunoprecipitation with strain-specific antibodies. Maturation of Edmonston strain MV was also suppressed. When the coinfected fused cells were selected with G418, Biken viral proteins remained at a constant level for up to 7 weeks. Wild-type MV proteins gradually decreased to a barely detectable level after 4 weeks and became undetectable after 7 weeks. Immunofluorescence studies showed a steady decline in cells expressing wild-type MV proteins in the coinfected cultures. These results suggest that Biken strain SSPE virus dominantly interferes with the replication of wild-type MV. The possible mechanisms of dominant interference and the implication for evolution of a persistent MV infection are discussed.