Quantification of NK subsets in different clinical groups. Whole blood from HC (n = 16), patients with HUS (n = 14), UC (n = 5), and IC (n = 6) was stained with PECy5-labeled anti-CD3, PE-labeled anti-CD56, and FITC-labeled anti-CX₃CR1 and analyzed by flow cytometry as described in “Patients, materials, and methods.” (A) Representative dotplots from a healthy child and a child with HUS. By gating on CD3⁻ lymphocytes, and according to CD56 and CX₃CR1 membrane expression, NK cells are classified into CD56^dim and CD56^bright. The value in each quadrant represents the percentage relative to the total number of NK cells. (B) Each bar represents the percentage of CD56^dim NK cells relative to the total number of lymphocytes, expressed as the mean ± SEM for each clinical group: HC (n = 16), patients with HUS (n = 14), UC (n = 5), and IC (n = 6). (C) Each bar represents the percentage of CD56^bright NK cells relative to the total number of lymphocytes, expressed as the mean ± SEM, within each clinical group: HC (n = 18), patients with HUS (n = 16), UC (n = 9), and IC (n = 8). **P < .005 compared with control groups.