(A) Immunolabelling for CD11b, a microglial activation marker (green fluorescence), revealed intense and widespread staining throughout the hippocampus of SE animals pre-treated with vehicle (n = 7; Ai, iii), which was reduced by IVIg (n = 4; Aii, v). Cell nuclei are shown in blue (DAPI staining). CD11b-positive cells in vehicle-treated SE mice (Aiv, arrow) displayed the typical morphology of activated microglia, i.e. a larger cell body with short, thickened radial processes. (B) Quantification of CD11b-positive cell numbers in the CA1 region of the hippocampus. Note that IVIg pre-treatment significantly reduced CD11b-positive cell numbers. (C) Staining for CD68 (red fluorescence) and iba1 (green fluorescence) in the hippocampus of control, vehicle and IVIg post-treated SE animals. Cell nuclei are again shown in blue. Note the significant increase in microglial activation (CD68) and density (Iba1) in vehicle but not IVIg post-treated SE mice. (D,E) Quantification of CD68- and iba1-positive cell numbers in the CA1 region of the hippocampus of 8 vehicle post-treated SE animals and 8 IVIg post-treated animals. Scale bar = 500 μm. Data represent mean ± standard error of the mean. *p < 0.05; ****p < 0.00005.