MOLECULAR BASIS OF MEASLES VIRUS PERSISTENCE: STUDIES OF AN SSPE TISSUE CULTURE MODEL (SUBACUTE SCLEROSING PANENCEPHALITIS)

Abstract

Subacute sclerosing panencephalitis (SSPE) is a degenerative, fatal neurologic disease of children, the consequence of persistent measles virus (MV) infection. A defective matrix (M) protein, one of the virion structural proteins, has been associated with SSPE. Defects in viral hemagglutinin and fusion proteins may also contribute to MV persistence. A unique SSPE-like tissue culture model, the IP-3-Ca cell line, which was derived from SSPE brain and which transfers viral macromolecules by cell-to-cell contact without viral release, was used to examine the molecular bases of MV persistence.;Protocols were designed to examine isolation attempts to recover infectious virus, immunocytochemical identification of MV-specific polypeptides, SDS-PAGE and protein kinetics analyses of immunoprecipitated viral gene products, and ultrastructural studies of persistent MV infections. All analyses included comparative studies of cells acutely infected with Edmonston MV.;IP-3-Ca cells failed to release virions upon cocultivation or fusion, were not temperature sensitive, and could not be activated to release virus by trypsin treatment. By lysing many cells in small volumes of medium, very low levels of infectious virus which displayed properties similar to Edmonston MV could routinely be recovered.;Immunofluorescence studies revealed MV antigens in IP-3-Ca cells similar to those in Edmonston MV-infected cells with one exception. The NP proteins of IP-3-Ca cells and IP-3-Ca-derived, infectious virus appear to have a different primary structure than Edmonston NP protein as determined by mouse monoclonal IgG specific for Edmonston NP.;SDS-PAGE analysis revealed that IP-3-Ca cells synthesized all the MV-specific polypeptides including a matrix protein. However, the M protein of IP-3-Ca failed to accumulate. Kinetics studies determined that while rates of synthesis of IP-3-Ca and Edmonston viral proteins were similar, the rate of turnover of IP-3-Ca matrix protein was four times faster than that seen in Edmonston MV. Viral isolates of IP-3-Ca origin synthesized all the MV polypeptides including a relatively stable matrix protein.;Ultrastructural studies revealed morphologic differences between intracytoplasmic nucleocapsids of acute and persistent infections, and unique intranuclear nucleocapsid-associated structures in IP-3-Ca cells.;These data suggest that SSPE viral persistence may result from multiple viral defects coupled with host cell restrictions placed upon complete viral replication.