Lung Vaso-Occlusion in Sickle Cell Disease Mediated By Arteriolar Neutrophil-Platelet Micro-Emboli

Background: Vaso-occlusive crisis (VOC) is the primary reason for emergency medical care by sickle cell disease (SCD) patients. SCD patients hospitalized with VOC often develop acute chest syndrome (ACS), a form of acute lung injury, suggesting a role for pulmonary vaso-occlusion in the onset of ACS. However, the cellular, molecular and biophysical mechanism of pulmonary vaso-occlusion is unknown.

Methods: SCD transgenic or non-sickle control mice were intravenously (IV) challenged with 2 to 3 ng of bacterial lipopolysaccharide (LPS). Fluorescent anti-mouse Ly-6G and CD49b mAbs were administered IV for in vivo staining of circulating neutrophils and platelets, respectively. Multiphoton excitation enabled quantitative fluorescence intravital lung microscopy (qFILM) was used to determine the molecular mechanism of pulmonary vaso-occlusion in live mice. Function-blocking anti-mouse P-selectin mAb (Fab fragments) was administered IV to assess the role of platelet P-selectin in promoting pulmonary vaso-occlusion.

Results: A nanogram dose of IV LPS selectively triggered pulmonary vaso-occlusion in SCD but not control mice. Remarkably, pulmonary vaso-occlusion involved occlusion of the pre-capillary pulmonary arteriole bottle-necks (junction of an arteriole and capillaries) by large neutrophil-platelet embolic aggregates. IV administration of Fab fragments of function blocking anti-P-selectin mAb led to the resolution of pulmonary vaso-occlusion, which was primarily mediated by the attenuation of large neutrophil-platelet aggregates into smaller aggregates that are not stopped by the arteriolar bottle-necks.

Conclusion: These results establish the relevance of neutrophil-platelet aggregation in pulmonary arterioles in promoting pulmonary vaso-occlusion in SCD and also highlight the therapeutic potential of inhibiting platelet P-selectin to prevent ACS in SCD patients hospitalized with VOC.

Acknowledgments: This study was supported by 1R01HL128297-01 (P.S.), AHA 11SDG7340005 (P.S.), VMI startup funds (P.S.). M.F.B. was supported by NIH-NHLBI training grant T32HL110849 and NIH-NHLBI F32 NRSA 1F32HL131216-01.