Quantification of NK cells in whole blood from 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 and PE-labeled anti-CD56 and analyzed by flow cytometry as described in “Patients, materials, and methods.” (A) Representative dotplots from 1 child within each clinical group showing NK (CD3⁻CD56⁺) and NKT (CD3⁺CD56⁺) subpopulations in the lymphocyte gate. Dot plot quadrants are defined as: CD3⁺/CD56⁺, top right; CD3⁻/CD56⁺, top left; and CD3⁺/CD16⁻, bottom right. The percentages of the different subpopulations are shown within each quadrant. (B) Each bar represents the mean ± SEM of the percentage of NK cells (CD3⁻CD56⁺) relative to lymphocytes. *P < .005 compared with MC.