Since its first isolation in 1954, measles has been considered to be an antigenically stable virus1,2, a view supported by numerous epidemiological studies demonstrating that a single exposure to measles confers life-long immunity on the infected host3. The basis for protection against recurrent infection is thought to be the production of polyclonal neutralizing antibodies that recognize a virus existing in only one, invariant antigenic form. Indeed, comparison of several independent isolates of measles virus for biological parameters such as cytopathic effect (CPE), host range and haemagglutination has supported the view that variation in measles virus is uncommon4,5. However, there has been no evaluation of variation at the molecular level by rigorous biochemical analysis of measles virus strains and of their structural proteins. We report here the isolation and characterization of spontaneously arising antigenic variants of measles by immunoselection, using neutralizing monoclonal antibodies directed against antigenic determinants of the Edmonston measles haemagglutinin protein. One of these variants has been shown to be antigenically similar to a low-passage ‘street’ virus isolate of measles, which suggests possible antigenic variation outside the laboratory.
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