Granulocyte macrophage-colony stimulating factor (GM-CSF) upregulates toll-like receptor (TLR) 4 and CD14 expression via extracellular signal-regulated kinase (ERK) 1/2 and p38, respectively. (A, B) Microglia were pretreated with U0126 or SB 203580 for 1 h before stimulation with 20 ng/ml GM-CSF for 48 h. Surface expression levels of TLR4 were assessed by flow cytometry (FCM) (A). Data indicate mean ± SD of three independent experiments; P < 0.001 (between GM-CSF and GM-CSF + U0126), P < 0.05 (between NT and GM-CSF + U0126). Surface expression levels of CD14 were assessed by FCM (B). Data indicate mean ± SD of three independent experiments; P < 0.001 (between GM-CSF and GM-CSF + SB 203580); P > 0.05 (between NT and GM-CSF + SB 203580). (C) Microglia were treated with 20 ng/ml GM-CSF. Then cells were lysed and total cell lysates were analyzed by western blotting for p-ERK1/2, ERK1/2, p-p38, and p38. Data are representative of two independent experiments.