Figure 4. Immunofluorescence and immunohistochemical analyses with human astrovirus Puget Sound capsid antibodies. A) Indirect double immunofluorescence–stained, formalin-fixed, paraffin-embedded tissue sections from 15-year-old boy with X-linked agammaglobulinemia and astrovirus encephalitis and a control with astrogliosis not caused by astrovirus infection. The sections were stained for the astrocyte marker glial fibrillary acidic protein (GFAP, green) and for viral capsid protein (rabbit serum 1:1,000, red). Viral capsid protein is present in hypertropic astrocytes throughout the subcortical white matter and cortex; astrocytes have swollen cell bodies with intense GFAP immunostaining. Blue signal (DAPI) indicates nuclear counterstaining. Original magnification ×100. B) Immunohistochemical localization of viral antigen in a frontal cortex biopsy specimen. Immunoalkaline phosphatase stain with viral capsid antibodies (rabbit serum 1:1,000) and naphthol-fast red with hematoxylin counterstain. Original magnification ×158.