Papovavirus antigens in paraffin sections of PML brains.

Brain tissue of 36 patients with definite PML (showing histologically the pathognomonic "PML cells") and of 12 cases with possible PML (showing patchy demyelination without PML cells) were studied for the presence of papovavirus antigens. A cross-reactive genus-specific serum and a serum raised against JCV were used in the peroxidase-antiperoxidase technique on formalin-fixed paraffin sections of autopsy brain. There was some variability in intensity of staining between the cases and between the sera. Papovavirus antigen-containing cells--mainly PML cells--were found in 35 definite and in one possible PML case. Twenty-nine of these brains reacted with anti-JCV serum. In five brains, antigen deposits were prominent in cytoplasm and processes of astrocytes in some areas of PML lesions. Giant astrocytes demonstrated viral antigens in six cases, indicating that these cells are indeed infected in PML. There was no staining of nerve cells or endothelial cells.