Figure 9

A defective phenotype of IRF8-deficient microglia in vivo in the cuprizone-induced demyelination model. (A) There was no quantitative difference in corpus callosal microglia, myelinating oligodendrocytes, and NG2-positive oligodendroglial precursor cells between Irf8 ^+/+ and Irf8 ^-/- mice before cuprizone feeding. Microglia and myelinating oligodendrocytes were identified by immunoreactivity for nuclear PU.1 and for the cytosolic CC1 epitope, respectively. (B) Cuprizone-mediated demyelination in the medial corpus callosum in Irf8 ^+/+ and Irf8 ^-/- mice. Representative LFB-PAS-stained paraffin sections of the medial corpus callosi of Irf8 ^+/+ and Irf8 ^-/- mice at 4 and 6 weeks of cuprizone diet (left panel). Scale bar: 100 μm. Reduction of myelinating oligodendrocytes in the corpus callosum. CC1⁺ oligodendrocytes per unit area of 6 μm-thick coronal sections were counted. At least three mice were used for each data point (right graph). (C) Microglial accumulation in the corpus callosum was delayed in Irf8 ^-/- mice compared with Irf8 ^+/+ mice. CD11b⁺ microglia with PU.1⁺ nuclei were quantified in 6 μm-thick coronal sections as in B (right graph). Note that the abnormal oval cell shape of activated Irf8 ^-/- microglia at 6 weeks of cuprizone feeding. Scale bar: 100 μm. (D) Oil red O plus hematoxylin staining of the corpus callosum of Irf8 ^+/+ and Irf8 ^-/- mice at 0, 4 and 6 weeks of cuprizone feeding. Lipid-rich myelin debris visualized by Oil red O staining (red arrows) rapidly accumulated in the corpus callosum of Irf8 ^-/- mice, as demyelination progressed. Scale bar: 25 μm. Data are presented as mean ± standard error. *P < 0.05 by Mann-Whitney U test.