CX₃CR1 expression in whole blood. Whole blood from HC (n = 10), patients with HUS (n = 19), IC (n = 10), and UC (n = 14) was stained with FITC-labeled anti-CX₃CR1 and analyzed by flow cytometry as described in “Patients, materials, and methods.” (A) Representative dotplot of FSC versus SSC showing typical circulating leukocyte populations. Representative dotplots of FSC versus FITC fluorescence of (B) 1 healthy child and (C) 1 child with HUS, showing CX₃CR1 expression in mononuclear populations. The corresponding isotype control is also presented. (D) Percentage of CX₃CR1 cells among mononuclear cells was calculated according the gates indicated in panels B and C for the different clinical groups. Results are expressed as means ± SEM. **P < .001 compared with all clinical groups using the Mann-Whitney U test.