Progressive multifocal leukoencephalopathy (PML) is a rare yet deadly brain disease caused by the JC virus. The mechanism for this infection is that the JC virus's specific tissue tropism is for the glial brain support cells.
Interestingly, the JC virus is exceedingly common, but usually is completely asymptomatic. Over 80% of the human population has been exposed to the virus, usually without any issues.
The ties to JC virus took a long while to discern because JC virus only seems to cause PML in very immunosuppressed patients. For instance, leukemia patients recieving irradiation, or HIV-positive patients. This confounded researchers' understanding of the origins of the disease because it suggested that one of the two diseases may have somehow had a hand in the development of PML.
Because of the critical nature of glia in the human nervous system, researchers had no real way of studying the disease in vivo or in vitro. In order to study and potentially cure the disease in the future, Steven Goldman and his team at the University of Rochester have developed a model of PML in mice, as is described in the Journal of Clinical Investigation. Using the model, Goldman and colleagues concluded that JC virus selectively destroyed astrocytes and glial progenitor cells (GPCs), not oligodendrocytes as previously assumed.
In reality, JC virus functionally depletes by astrocytes and oligodendrocytes, as astrocytes nourish and support oligodendrocytes, and when they disappear, so too do the ODCs.
Brains affected by PML. From http://acelebrationofwomen.org/wp-content/uploads/2011/04/pml2.jpg.