Neutrophil infiltration following ICH is attenuated in TLR2 KO mice. (A-B) WT and TLR2 KO mice (n = 3) were subjected to collagenase-induced ICH. After 24 h, brains were dissociated, and the percentages of leukocytes (Leu; CD45hi, CD11b+), macrophages (M; CD45hi, CD11b+, Gr-1low), neutrophils (Neu; CD45hi, CD11b+, Gr-1hi), and microglia (Mg; CD45int, CD11b+) present in ICH-injured brain were determined by flow cytometry. Data are presented as mean ± SEM (** p < 0.01, * p < 0.05). (C-F) At 24 h (C and E) and 72 h (D and F) following collagenase injection, brain sections of WT and TLR2 KO mice (n = 5) were immunostained with anti-Gr-1 antibodies to detect neutrophil infiltration. Scale bars: 50 μm. (G) MPO activity (U/g) was measured in the ipsilateral brain hemisphere of WT and TLR2 KO mice 24 h post-ICH. Data are expressed as mean ± SEM (*** p < 0.001, vs. collagenase-injected WT mice, n = 5). (H) Total RNA was isolated from ipsilateral hemorrhagic tissue (AP, 0.0 to −2.0 mm) 6 h post-ICH and used for quantitative real-time RT-PCR to measure TNF-α mRNA levels. Data are expressed as mean ± SEM (* p < 0.05, ** p < 0.01 vs. collagenase-injected WT mice, n = 3).