Histomorphometry of microglia response. The picture sequence demonstrates the morphological and spatial changes of microglia in response to experimental bacterial meningitis due to infection with S .pneumoniae. Microglial staining was performed by staining AIF-1 and sections were observed using a 20 × (pictures A, C and E), respectively 40 × (pictures B, D and F) magnifying objective. The resting microglia (picture A and B) transforms from a ramified to an amoeboid, phagocytic phenotype during the early acute phase of the disease (pictures C and D). Three days after infection we find a pronounced infiltration of microglial cells into the subgranular zone of the dentate gyrus (highlighted by dotted lines) where neuronal apoptosis occurs (picture E and F). The transformation and redistribution of the resting microglia to the site of tissue damage is in well agreement with the transcriptional data shown in figure 9.