AIDS - Oligodendroglial infection in progressive multifocal leukoencephalopathy: This photomicrograph is taken from a lesion of PML, labeled histochemically (brown) for JC viral sequences after in situ nucleic acid; hybridization. The JC virus has a propensity to infect glia, especially oligodendroglia, as shown here. One result of this infection is the local degeneration of myelin normally maintained by the infected cells, resulting in a multifocal demyelinative process. Macrophages and reactive astrocytes are induced by this demyelinative process but are inconspicuous in the background in this photograph.