Progressive multifocal leukoencephalopathy: JC virus detection by in situ hybridization compared with immunohistochemistry.

In four cases of progressive multifocal leukoencephalopathy (PML), we compared biotin-labeled DNA:DNA in situ hybridization with peroxidase immunohistochemistry for the detection of JC virus (JCV). The localization of JCV DNA and JCV capsid protein was compared in formalin-fixed, paraffin-embedded brain tissues. Infected oligodendrocytes showed both JCV DNA and JCV protein. However, bizarre astrocytes demonstrated JCV capsid protein less often than JCV DNA. In situ hybridization with a biotinylated probe was as sensitive and specific as immunohistochemistry for diagnosis on formalin-fixed tissue. The presence of both JCV DNA and viral capsid protein in bizarre astrocytes suggests that these cells are neither truly transformed nor permissively infected, but are distinctively altered by JCV.