Fig. 9.

Reactive astrogliosis in response to CNS tumors. a High magnification image of autopsy specimen from a man with widely infiltrating primary CNS lymphoma. Two color immunohistochemistry for GFAP and the cell cycle marker Ki67, shows the cytoplasm of reactive astrocytes stained blue (arrows), with nuclei of infiltrating, malignant and highly proliferative lymphoid elements stained brown (arrowheads). Note that essentially none of the GFAP-immunoreactive astrocytes show Ki-67-immunoreactive nuclei and are thus not proliferative and exhibit only a moderate degree of reactive astrogliosis with cell hypertrophy and up regulation of GFAP, in spite of the presence of numerous infiltrating lymphoma cells. b High magnification image of a medulloblastoma immunohistochemically stained for GFAP and showing many processes of reactive astrocytes along one edge of the tumor (at right of figure). Scale bars a 15 μm, b 25 μm