Neutrophils disturb pulmonary microcirculation in sepsis-induced acute lung injury

Abstract

The lung is highly vulnerable during sepsis, yet its functional deterioration accompanied by disturbances in the pulmonary microcirculation is poorly understood. This study aimed to investigate how the pulmonary microcirculation is distorted in sepsis-induced acute lung injury (ALI) and reveal the underlying cellular pathophysiologic mechanism.Using a custom-made intravital lung microscopic imaging system in a murine model of sepsis-induced ALI, we achieved direct real-time visualisation of the pulmonary microcirculation and circulating cellsin vivo. We derived the functional capillary ratio (FCR) as a quantitative parameter for assessing the fraction of functional microvasculature in the pulmonary microcirculation and dead space.We identified that the FCR rapidly decreases in the early stage of sepsis-induced ALI. The intravital imaging revealed that this decrease resulted from the generation of dead space, which was induced by prolonged neutrophil entrapment within the capillaries. We further showed that the neutrophils had an extended sequestration time and an arrest-like dynamic behaviour, both of which triggered neutrophil aggregates inside the capillaries and arterioles. Finally, we found that Mac-1 (CD11b/CD18) was upregulated in the sequestered neutrophils and that a Mac-1 inhibitor restored the FCR and improved hypoxaemia.Using the intravital lung imaging system, we observed that Mac-1-upregulated neutrophil aggregates led to the generation of dead space in the pulmonary microcirculation that was recovered by a Mac-1 inhibitor in sepsis-induced ALI.

Differences in Inflammation, Apoptosis and Tissue Hypo-perfusion Indicators Caused by Using Two Different Gauges in Cecal Ligation and Puncture-induced Rat Models of Sepsis

“…(13) It is demonstrated that the size of the needle used in the CLP procedure can be in uential in different septic outcomes such as mortality, cytokines concentrations, apoptosis, lactic acidosis, and autophagy. Previous studies showed that G-18 and G-21 induced sepsis more e ciently compared to other gauge groups (6,11,12).…”

“…Pulmonary complications of sepsis develop as a result of the cumulative effect of circulating cellular elements, soluble in ammatory mediators, and cytokines on the pulmonary tissues. (6) The main underlying mechanism of lung injury during sepsis is demonstrated to be acute alveolar in ltration and changes in respiration ratio (7).…”

Ventilation and Perfusion at the Alveolar Level: Insights From Lung Intravital Microscopy

“…Vacuum suction stabilized lung windows are now widely used to analyze the pulmonary immune system (Looney et al, 2011). This includes neutrophil margination (Kuebler et al, 1994(Kuebler et al, , 1997Park et al, 2019) or immune cell -tumor cell interactions (Hanna et al, 2016), as well as infections of the lung (Sewald, 2018;Ueki et al, 2018).…”

“…In recent years, this limitation has been overcome by e.g., combinations of fluorescent dyes and antibodies to differentiate leukocyte subsets. To address the role of neutrophils in a model of sepsis-induced lung injury, Park et al (2019) labeled erythrocytes ex vivo with DiD and reinfused them via a catheter. Concomitantly, vessels were visualized with FITC and Tetramethylrhodamine (TMR) conjugated dextran and neutrophils were specifically labeled in vivo with an anti-Ly6G + monoclonal antibody tagged with a fluorophore.…”

<p>NLRP3 Regulated CXCL12 Expression in Acute Neutrophilic Lung Injury</p>

“…[6][7][8] In animal models, the depletion of neutrophils reduces the severity of lung injury. 9 A promising therapeutic target would be to inhibit neutrophil recruitment, rather than eliminating them, in ALI. 4 In ARDS, chemokine levels are elevated in the lungs and correlate with outcome.…”