CD11b and MHC-II expression in hippocampi of aged female mice detected by immunohistochemistry and flow cytometry. Seven days after KA treatment, the number of activated microglia was greater in WT mice (A) than in IL-18 KO mice (B) with similar neuropathological changes. Very few activated microglia were found in the hippocampi of saline-treated mice (C) and negative controls with omission of the primary antibody showed no positive staining (D). CD11b positive cells were shown as dark brown in color. By flow cytometry, microglia of hippocampi were identified as a homogeneous population of CD11b+/CD45low/moderatecells (E). The proportion of MHC-II positive cells was higher in WT mice (n = 5) than in IL-18 KO mice (n = 6) after KA treatment. Before KA delivery, there was no difference of MHC-II positive cells between the two groups (F). *P < 0.05. Bars = 100 μm.