Role of platelet-eosinophil interactions in COPD morbidity

PROJECT SUMMARY / ABSTRACT Identification of targeted therapies for chronic obstructive pulmonary disease (COPD), a leading cause of morbidity and mortality in the United States and globally, has lagged other lung diseases. Eosinophil count, which has been a good biomarker for identifying type-2 inflammation and response to monoclonal therapies in asthma has proven to be less beneficial in COPD with unclear molecular mechanism. Since COPD is a heterogenous disease marked by systemic inflammation and high comorbidity burden it is critical that the impact of dysfunctional platelets, which act as immune and inflammatory cells, is considered in the mechanistic pathway of type-2 inflammation and eosinophil activation. Mounting evidence suggests that the magnitude of platelet activation, independent of cardiovascular comorbidity, is associated with respiratory outcomes in COPD. Activated platelets conjugate to eosinophils which leads to eosinophil activation and translocation into the lung tissue. Understanding the role of platelet-eosinophil conjugates in COPD morbidity and associations between platelet activation and eosinophil activity would enhance understanding of underlying mechanisms for type-2 inflammation in COPD and lead to novel therapeutic options. To elucidate the association of activated platelets with eosinophils in COPD we will directly measure platelet-eosinophil conjugates and eosinophil activation using flow cytometry in 50 individuals with COPD without overt or subclinical cardiovascular disease co-enrolled in the ongoing study "Platelet Activation Pathways and Respiratory Morbidity in COPD" (NHLBI K23HL151758). We hypothesize that a higher proportion of platelet-eosinophil conjugates and activated platelets as measured by flow cytometry will be associated with disease severity, worse respiratory symptoms, higher proportion of circulating activated eosinophils, and more type-2 inflammation. Platelet-eosinophil conjugates will be identified in whole blood as cells simultaneously expressing eosinophil (CCR3) and platelet (CD42a or P-selectin) surface markers in unstimulated and agonist-stimulated samples while activated eosinophils will be distinguished as those expressing CD69, CD63, CD29, or CD18. Proportion of activated platelets will be identified in platelet rich plasma before and after in vitro stimulation as part of the K23 study as those expressing P-selectin, CD63, CD40L, or PAC1. Completion of the proposed aims will elucidate the role of platelet-eosinophil conjugates and associations of activated platelets with eosinophil activation which will inform future pathway-specific mechanistic and interventional studies toward the ultimate goal of personalized therapy for COPD. The proposed study uses the infrastructure and refined laboratory protocols created as part of the K23 study to investigate the role of activated platelets with eosinophils. A more refined understanding of the mechanisms through which eosinophils are associated with COPD morbidity could potentially reveal more broadly applicable endotypes for targeted therapy.