In 1965, in collaboration with Marcus, we described an assay system for rubella virus growing under noncytopathic conditions.1Green monkey kidney cells infected with rubella virus were challenged with a high multiplicity of Newcastle disease virus (NDV) five days later and did not replicate the Newcastle disease virus. The replication of NDV was measured by a standard hemadsorption test with bovine erythrocytes. The rubella infected cells stood out as hemadsorption negative, since they did not produce hemagglutinin.
This noninterferon-mediated interference against superinfection with NDV has been called intrinsic interference.2 Subsequently, Sindbis and West Nile viruses,2polioviruses,2 lymphocytic choriomeningitis virus,3 infectious bronchitis virus,4 cytomegalovirus,5 and reovirus6 have also been shown to induce intrinsic interference when growing under noncytopathic conditions in a variety of tissue culture systems. We sought interference with the development of NDV hemadsorption as an assay system for serum hepatitis