Numerous astrocytes and neurons in the cortex of both cerebral hemispheres and at the gray-white junction and are infected by JCV. (A) Typical appearance of giant, bizarre astrocytes with multiple nuclei (arrrows) located in proximity to a neuron with an enlarged nucleus and marginated chromatin (arrowhead, bar= 25 μm). (B) Cortical pyramidal neurons harboring atypical nuclei 5 to 6 times their normal size with central clearing of the chromatin (arrows) are interspersed among unaffected cells. Bar= 25 μm. Hematoxylin and eosin stain. (C, D) Double immunohistochemistry staining for JCV T Ag (sc-20800, dark blue) and myelin and oligodendrocytes (C, CNPase, C5922, brown) or astrocytes (D, GFAP, M0761, light brown), displayed in 25,000,000 pixels pictures of a 1cm² representative area of cerebrum, shows a linear area of tissue necrosis at the gray-white junction (C,D, arrowheads), and patchy areas of cell loss in the cortex (D, arrows). Most JCV-infected cells (C, dark blue, arrows) which are located at the gray-white junction and the cortex, are not oligodendrocytes (C, inset, absence of staining for myelin (brown) in JCV-infected cells (blue, arrow)). Conversely, numerous JCV-infected astrocytes (D, inset, light brown cell with blue nucleus, arrowhead) can be found within or in proximity to areas of tissue necrosis, interspersed among JCV-infected non-glial cells with neuronal morphology (D, inset, arrows). Bars = 1mm. (E, F) Double immunofluorescence (IF) staining for the neuronal marker MAP-2 (E, M4403, F, AB5622, AlexaFluor 488, green) and for JCV T Ag (sc-20800) or VP1 (PAB597, AlexaFluor 568, red) shows that numerous neurons are infected by JCV and express T Ag (E, arrows) and/or VP1 (F, arrows), interspersed among JCV-infected glial cells (E, F, arrowheads), some of them with clear astrocytic morphology (E, asterisk). Bars = 50μm. GM, gray matter; GWJ, gray-white junction; WM, white matter.

Electron microscopy of a cortical area containing JCV infected neurons.
JCV VP1 immunoreactivity is demonstrated by electron dense DAB bound to anti VP1 ab clumping in the cytoplasm (Cy, arrow). Large amounts of 40 nm viral particles, consistent with the size of polyomaviruses, are present in the nucleus (Nu), close to the nuclear membrane (inset). Bar 2 μm.

Multiple cortical lesions are present in both cerebral hemispheres.
(A) Magnetic resonance imaging shows patchy areas of hyperintense signal in FLAIR images (TR: 8002.0 ms, TE: 128.4 ms, slice thickness 5 mm) in the temporal, parietal and frontal cortex bilaterally (arrows). (B) Three months later, additional cortical areas are affected, and the abnormal signal extend to the subcortical white matter (arrows).

Expression of NeuN confirms the neuronal phenotype of JCV-infected cells. (A) Double immunofluorescence (IF) staining for the neuronal marker NeuN (MAB377, AlexaFluor 488, green) and for JCV T Ag (AlexaFluor 568, red) confirm the presence of JCV-infected neurons expressing T Ag (arrows), interspersed among uninfected neurons. Bar = 25μm. (B–C) Double immunohistochemistry (IHC) staining for NeuN (MAB377, brown) and JCV T Ag (B, sc-20800, blue) or the VP1 capsid protein (C, PAB597, blue). Numerous JCV-infected neuron processes (B, C, arrows) contain JCV T-Ag and VP1 in their axons and dendritic processes (B, C, arrowheads). Bars = 50μm.