Cigarette Smoking Exacerbates Flu-Induced Thrombo-Inflammation

Rationale: 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.

Materials and methods: We have developed a two-hit model of CS-induced severe flu in mice. Mice were exposed to four weeks of room air (air) or CS followed by intra-nasal administration of A/PR/8/34 (H1N1) IAV. The body weight was measured every day for two weeks after IAV administration followed by assessment of lung injury at day 7 and 14. Lungs were harvested for histological assessment of lung injury and estimation of viral titer by RT-PCR. Quantitative fluorescence intravital lung microscopy (qFILM) was conducted at 2-, 3- and 4-days post IAV-infection to visualize dynamics of neutrophil and platelet recruitment in the lung of mice IV administered with fluorescent dextran, anti-Ly6G Ab and anti-CD49Ab.

Results: Mice exposed to CS+IAV manifested significantly more weight loss, lung injury, lung congestion and alveolar hemorrhage compared to mice administered room-air+IAV. QFILM revealed that severity of lung injury was associated with significantly more entrapment of neutrophil-platelet aggregates within the pulmonary microcirculation and infiltration into the air spaces of CS+IAV than room-air+IAV administered mice.

Conclusion: These initial results suggest that CS primes innate immune signaling in neutrophils and platelets to promote their recruitment in the lung following flu. Currently, studies are underway to identify innate immune pathways in neutrophils and platelets that drive this severe thrombo-inflammatory response.