Phagocytosis by neutrophils from critically ill patients is defective and related to C5a exposure. (A) Phagocytosis by patients' neutrophils is significantly reduced compared with healthy volunteers. ***P = .001 by Mann-Whitney U test. Data are shown as median (central line), interquartile range (box), and range (whiskers) (n = 39 participants: 29 patients and 10 healthy volunteers). (B) Relationship between surface CD88 expression and phagocytosis by neutrophils. P < .0001, r = 0.8 by Spearman rho. The solid line indicates phagocytosis predicted by linear regression at a CD88 of 250 GMF units, the predefined cutoff for neutrophil dysfunction (n = 29 patients). (C) Representative images of patient neutrophils exposed to zymosan before (left) and after (right) GM-CSF treatment (magnification ×32).