Our studies continue on the molecular pathology of JC virus and human glial cells in culture, and more recently, with human brain tissue sections from infected patients wth progressive multifocal leukoencephalopathy (PML). Experiments have focues at the intracellular level describing the nature of viral persistance in the CNS, pathogenesis of PML as a demyelinating disease, and the mechanisms of generic regulation of the viral and cellular genes involved. Our results include solving the biggest problems that working with JC has presented, namely the host and tissue restriction for growth to primary human fetal glial cells in culture. We have estalbished an immortalized line of human fetal astroglial cells using a mutant transforming gene of SV40. These cells are able to produce infectious JCV and have allowed us to examine the kinetics of CV DNA replication and T protein synthesis. We have also found that the SV40 T protein made in human glial cells complexes with a glial cell protein, p53, and stablizes this protein in the cell. The JCV T protein does not appear to complex with the p53 protein, perhaps due to confirmational differences between the T proteins of SV40 and JCV. Additional evidence for such differences came from our experiments suggesting alkylation of cycteine residues of the JCV T protein was necessary in order to resolve the immunoprecipitated T protein using denaturing gel electrophoresis. This was not necessary for either the T proteins of SV40 or the related human BK virus. Studies of paraffin embedded or fozen brain tissue from PML patients showed the presence of JCV DNA using in situ hyridization and correlated with the detection of viral capsid antigen using immunocytochemical tests. These studies also revealed that aligodendroglian cells are the main target for JCV gene expression but that bizarre astrocyctes present in PML plaques showed JCV DNA and capsid antigen. This latter finding questions role the of JC virus may have in the pathogenesis of malignant gliomas in the general population that has been suggested by others.