Fig 2: Schematic summary.AKI induces rapid intravascular neutrophil train formation in lung alveolar capillaries, a form of neutrophil retention. Rapid retention is enhanced by decreased deformability secondary to F-actin polymerization (submembrane F-actin bands) in circulating neutrophils that impedes their lung capillary passage. CCR2+ classical monocytes are required for neutrophil train formation and release CXCL2 to attract neutrophils into trains. Neutrophil train formation reduces alveolar capillary blood flow and is associated with thrombosis (thrombi contain both platelets and fibrin). This capillary perfusion defect leads to reduced oxygenation due to a ventilation perfusion mismatch, a scenario that differs from infectious inflammatory lung diseases, such as bacterial pneumonia or pulmonary alveolar edema in which ventilation is affected.

Fig 3: Schematic summary.AKI induces rapid intravascular neutrophil train formation in lung alveolar capillaries, a form of neutrophil retention. Rapid retention is enhanced by decreased deformability secondary to F-actin polymerization (submembrane F-actin bands) in circulating neutrophils that impedes their lung capillary passage. CCR2+ classical monocytes are required for neutrophil train formation and release CXCL2 to attract neutrophils into trains. Neutrophil train formation reduces alveolar capillary blood flow and is associated with thrombosis (thrombi contain both platelets and fibrin). This capillary perfusion defect leads to reduced oxygenation due to a ventilation perfusion mismatch, a scenario that differs from infectious inflammatory lung diseases, such as bacterial pneumonia or pulmonary alveolar edema in which ventilation is affected.

Fig 4: CCR2+ classical monocytes and CXCL2/CXCR2 signaling drive lung capillary neutrophil retention after AKI.(A) Schematic of classical monocyte depletion using anti-CCR2 Ab in vivo. (B) Lung monocytes after pretreatment with anti-CCR2 Ab or control IgG. n = 6 per group. (C) Serum BUN indicating kidney injury level on day 1 after AKI. n = 6 per group. (D) Lung immunofluorescence staining after AKI in control versus anti-CCR2 Ab–treated animals. Shown are alveolar and interstitial macrophages (CD68+, red) and neutrophils (Ly6G+, green). Hoechst 33342 dye (blue) was used to visualize nuclei. Scale bar: 100 μm. n = 6 per group. (E) Total number of cell-cell communications inferred by CellChat based on the scRNA-Seq analysis for sham-operated versus AKI mice (also see Supplemental Figure 2). (F) Cell-cell communications from monocytes or macrophages to neutrophils were predicted at single ligand-receptor resolution (unbiased); the neutrophil chemoattractant CXCL2 in monocytes and macrophages and their receptor CXCR2 in neutrophils was predicted to be significantly increased in AKI versus sham groups and are underlined. (G) Lung immunofluorescence staining for Ly6G+ neutrophils (green) from WT C57BL/6 mice injected with anti-CXCL2 or control Ab and subjected to AKI. Scale bar: 100 μm. n = 4–5 per group. The graph shows a quantification of lung neutrophils detected by immunofluorescence. Data represent the mean ± SD. *P < 0.05 and **P < 0.01, by unpaired, 2-tailed Student’s t test.