Samples were obtained from HIV-negative patients without PML (HIV −, PML −), HIV-positive patients without PML (HIV +, PML −) and HIV-positive patients with PML (HIV +, PML +) and analyzed by immunohistochemistry as described in Materials and Methods. Normal astrocytes in the cortex of a control brain were labeled with Glial Fibrillary Acidic Protein (Panel A, rhodamine), and showed no expression of Rad51 (Panels B, fluorescein and C, double labeling). Bizarre astrocytes within demyelination plaques in cases of Progressive Multifocal Leukoencephalopathy, also labeled for GFAP (Panel D, rhodamine), demonstrated numerous foci of Rad51 in the nuclei (Panels E, fluorescein and F, double labeling). JCV infected oligodendrocytes were labeled with VP1 (Panel G, rhodamine), highlighting the intranuclear viral inclusion body, and showed minimal foci of Rad51 in the same nuclear location (indicated by arrows in Panels H, fluorescein, and I, double labeling). All panels original magnification ×1000.