Involvement of JC Virus–Infected Mononuclear Cells from the Bone Marrow and Spleen in the Pathogenesis of Progressive Multifocal Leukoencephalopathy

PROGRESSIVE multifocal leukoencephalopathy (PML), a subacute demyelinating disease resulting from infection of oligodendrocytes by JC virus, occurs almost exclusively in immunocompromised patients.1 , 2 The pathogenesis of PML has remained obscure because the nature of the primary infection, the site of virus during latency, and the route by which JC virus enters the brain have not been determined. Previous studies indicating that JC virus may be present in systemic organs have reported urinary excretion of JC virus by pregnant women and patients receiving immunosuppressive drugs after transplantation.3 , 4 JC virus DNA has been detected by Southern blotting in tissue from the spleen, lymph . . .