PB1294 - Pulmonary thrombosis promotes sever flu in mice exposed to cigarette smoke.

Background: Epidemiological evidence suggests that prior exposure to cigarette smoke (CS) or habitual smoking increases the risk of influenza A virus (IAV)-triggered respiratory failure (severe flu). Although emerging evidence supports the role of thrombo-inflammation in the development of CS and IAV-triggered lung injury, the innate immune mechanism that contributes to this morbidity remains poorly understood.

Aims: To determine whether neutrophil-platelet aggregation and NETs generation in the pulmonary microcirculation promotes CS and flu-induced severe lung injury.

Methods: We used mouse model of 4-week long exposure to CS with subsequent infection with IAV A/PR/8/34 (H1N1) strain. The body weight changes and oxygen saturation were measured every day for 7 days post IAV infection followed by assessment of lung injury. Lungs were harvested for histological assessment and estimation of viral titer using RT-PCR. Quantitative fluorescence intravital lung microscopy (qFILM) was conducted 72-96 hours post IAV-infection to visualize the lung microcirculation of mice intravenously administered with fluorescent dextran, anti-Ly6G Ab and anti-CD49Ab to visualize pulmonary microcirculation, neutrophils and platelets, respectively.

Results: Mice exposed to CS+IAV manifested significantly more weight loss, drop in oxygen saturation and lung injury compared to mice exposed to room-air+IAV. qFILM revealed that severity of lung injury in CS+IAV exposed mice was associated with significantly larger regions with impaired blood flow and vascular leakage in the lung, which was secondary to significantly more pulmonary vascular occlusion by platelet-rich neutrophil-platelets aggregates in mice exposed to CS+IAV than room-air+IAV .

Conclusion(s): These initial results suggest that CS primes pro-thrombo-inflammatory signaling in neutrophils and platelets to promote severe lung injury following flu.