SSPE‐BIKEN: A Naturally arising hemagglutination‐defective mutant of measles virus

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Abstract
Biochemical and genetic methods have been used to investigate a defective variant of measles virus previously isolated from a patient with subacute sclerosing panencephalitis (SSPE). Since its isolation, this syncytiogenic strain (SSPE‐BIKEN) has remained cell‐associated; infected cells do not hemadsorb and do not release infectious virus. Immune precipitation and polyacrylamide gel electrophoresis were used to study the synthesis of measles virion proteins in SSPE‐BIKEN‐infected cells. All of the virion proteins were detected in immune precipitated whole cell extracts. However, the hemagglutinin (HA) protein was not detected on the cell surface by lactoperoxidase iodination. These results suggest that the failure of the HA protein to insert into the cell membrane accounts for the block in the release of infectious virus. Radioactively labeled, noninfectious, virus‐like particles have been purified from the media of SSPE‐BIKEN‐infected cells. These particles contain virus nucleocapsid, nucleocapsid‐associated, and membrane proteins, but very little HA and hemolysin proteins. Genetic complementation between SSPE‐BIKEN and a temperature‐sensitive mutant of measles virus was observed and suggests that the SSPE isolate defect is due to a mutation. Additional evidence of a mutation is provided by the detection of low frequency revertant progeny in SSPE‐BIKEN stocks. Our results support the hypothesis that genetic variants of measles virus are involved in the etiology of SSPE.