Blocking IL-1 reduces microglia activation. Hippocampi were harvested at days 1, 3, and 7 after lipopolysaccharide (LPS) administration and stained with anti-CD11b. Pictures show CA1 (scale bar 50 μm, 20×) and photomicrographs were blindly scored and microglia activation was graded on a scale 0 (lowest) to 3 (highest). (a, e and i) normal controls; no microgliosis was observed in wild type nor IL-1R-/-. Panel 1: LPS. Reactive microglia were found at days 1 and 3 (c and d) after LPS injection compared with (b) naive. Resting microglia (box a, 40×) shifted to a 'reactive state' (box b, 40×). Panel 2: IL-1Ra. Reduction in the number of reactive microglia was observed (g and h) after administering IL-1Ra both at days 1 and 3, (f) with no changes from controls. Panel 3: IL-1R-/-. (j to l) Administration of LPS to IL-1R-/- did not induce microglia activation at any time point assessed. Immunohistochemical grading (0 to 3) illustrates panels 1, 2, and 3. One day after LPS administration we found clear microgliosis, which was attenuated by IL-1Ra treatment (day 1 ** P < 0.001 vs naïve, day 3 * P < 0.05 vs naïve). Significant reduction in microgliosis was found both after IL-1 Ra administration and in IL-1R-/- (n = 4). Non parametric data are presented with Kruskal-Wallis followed by Dunn's test.