GM-CSF attenuates innate immune activation. Photomicrographs and enumeration of anti-CD11b+ microglia in the SN of mice treated with PBS, MPTP (16 mg/kg × 4 doses), or pretreated with 50 μg GM-CSF/kg followed by MPTP A. Midbrains from mice 2 d after MPTP treatment stained with anti-Mac-1 Ab, HRP-conjugated secondary Ab, and visualized with DAB. Activated microglia are identified as those stained cells exhibiting large amoeboid cell bodies and shortened processes. B. Differences in mean ± SD (n = 5 per group) were determined where p < 0.05 compared with groups treated with aPBS, bMPTP, or cGM-CSF pretreated and MPTP (GMCSF Pretreatment).