Phenotypic analysis of ICAM-1 KO mice and role in platelet-monocyte interaction. Platelet reactivity in blood from ICAM-1 KO, compared with WT mice, were no different following (A) collagen or PAR4 amide stimulation, but were significantly inhibited in response to 0.3 μM U46619 (n = 6 for all). (B) Flow cytometric imaging (×60 objective) of samples stimulated by U46619 (0.3 μM) revealed a potential difference in platelet (green) monocyte (red) interactions. Scale bars represent 7 μm. (C) Quantitation of these interactions identified significantly more platelet-monocyte interactions upon U46619 stimulation in WT mice compared with ICAM-1 KO mice. In WT mice, this interaction was exaggerated when blood was prestimulated with mTNF-α but reversed when performed in the additional presence of eptifibatide or the fibrinogen peptide γ-117-133. The level of interaction in ICAM-1 KO mice remained constant through all conditions (n = 3 for all). (D) Corresponding representative histograms of platelet (CD42d-PE) binding of the Ly6C (monocyte)-positive population in WT (left) and KO (right) mice in absence (red) and presence (blue) of eptifibatide. Data presented as mean ± SEM, *P < .05 by 2-way ANOVA.