CXCR4 regulates pulmonary monocyte margination and predisposition to injury. (A) Schematic of the lung efflux assay. (B) Monocyte numbers released from the lung vasculature after indicated treatments. Results expressed as mean (n = 5–7 per group) and representative of one out of three independent experiments. ns, not significant; *, P < 0.05; **, P < 0.01; ***, P < 0.001 (one-way ANOVA). (C and D) Frequency of blood (C) and pulmonary release (D) of CD14⁺CD16⁻ classical monocytes in humanized mice at baseline and 2 h after AMD3100 treatment (n = 8–11). Results are representative of one out of two independent experiments. **, P < 0.01 (Student’s t test). (E) Net monocyte release from the lungs of two individual nonhuman primates (Macaca fascicularis) over a 4-h observation period. (F–H) Lyz2^creCxcr4^fl mice were compared with Cxcr4^fl control mice for lung vascular leakage during acute lung injury (F; n = 5; **, P < 0.01, Student’s t test) or fold-increase accumulation of lung Ly6C^hi (left) and Ly6C^lo (right) monocytes (G; n = 3–5; ***, P < 0.001, Student’s t test) and their mortality using the Kaplan-Meier survival curve (H; n = 10; ****, P < 0.0001, Mantel-Cox) in the CLP sepsis model. Results are representative of one out of three independent experiments.