REEVALUATION OF A CASE OF PROGRESSIVE MULTIFOCAL LEUKOENCEPHALOPATHY PREVIOUSLY DIAGNOSED AS SIMIAN-VIRUS 40 (SV40) ETIOLOGY

A case of progressive multifocal leukoencephalopathy (PML) reported pr eviously to be of simian virus (SV40) etiology was re-evaluated. The s upernatant from a 10% homogenate of brain material was inoculated into African green monkey kidney cells and BSC-1 cells which are permissiv e for SV40. However no cytopathic effect (CPE) developed and no virus was isolated. The brain supernatant agglutinated human group O erythro cytes and contained 5120 units/mL. The Hirt supernatant from the brain contained three DNA bands corresponding to forms I, II and III of cir cular double-stranded viral DNA. Restriction endonuclease cleavage ana lysis revealed that this viral DNA was different from SV40 DNA, but si milar to JC virus DNA. After cloning of this viral DNA into pBR322 at the BamHI site, DNA homology of this virus and of SV40 was investigate d. The cloned DNA hybridized with all four HpaI/EcoRI fragments of SV4 0 genome at the effective temperature (Tm) of -50-degrees-C. At Tm -28 -degrees-C, however, the cloned DNA hybridized with only HpaI/EcoRI fr agment B of the SV40 genome. In contrast to this, JC virus DNA hybridi zed with all five EcoRI/BamHI/HindIII fragments of cloned DNA even at Tm -28-degrees-C. Therefore, the causative agent of this PML case was not SV40 but JC virus.