Flow Cytometric Detection of Platelet-Monocyte Aggregates in patients with Chronic Obstructive Pulmonary Disease

Abstract

SUMMARY I nflammation and haemostasis are interrelated pathophysiological processes that considerably affect each other in bidirectional relationship in which the two systems function in a positive feedback loop. The extensive crosstalk between immune and haemostatic systems occurs at level of all components of the haemostatic system including vascular endothelial cells, platelets, plasma coagulation cascade, physiologic anticoagulants and fibrinolytic activity. During inflammatory response, inflammatory mediators, in particular proinflammatory cytokines, play a central role in the effects on haemostatic system by triggering its disturbance in a number of mechanisms including endothelial cell dysfunction, increased platelet reactivity, activation of the plasma coagulation cascade, impaired function of physiologic anticoagulants and suppressed fibrinolytic activity. The interaction between inflammatory cells and activated platelets is important in the pathogenesis of atherothrombosis and may contribute to cardiovascular risk in patients with COPD. PMA are formed when activated platelets release inflammatory chemokines and recruit inflammatory cells which is an early process in atherothrombosis. Circulating PMA is considered a sensitive measure of platelet activation. The level of PMA reflects the degree of platelet hyperactivity thus providing a robust index of blood thrombogenicity. However, cross-talk between platelets and monocytes is now regarded as a crucial pathophysiological mechanism linking thrombosis and inflammation and is believed to mediate, at least in part, the pro-inflammatory action of activated platelets. Thus, platelet activation represents a novel mechanism linking COPD, inflammation and cardiovascular disease. The aim of this study was to identify the presence of a hypercoagulable state in patients with COPD by studying the level of PMA as a marker of platelet activation in stable COPD patients and during its acute exacerbation, in addition to assaying its level in healthy control subjects. The study was conducted on 45 adult male subjects, their age group ranged from (42-65 years). They were categorized as 15 patients with stable COPD (stable group), 15 patients with acute exacerbation of COPD (exacerbation group) and 15 healthy subjects having no history of respiratory symptoms as the control group. The patients were diagnosed as COPD according to GOLD 2014 and they were admitted to the chest department of Ain Shams University hospitals. After taking an informed consent, peripheral venous blood samples were obtained from all subjects included in the study and flow-cytometric analysis was performed for detection of PMA using suitable monoclonal antibodies. They were well-matched for age and prior smoking habit to rule-out the effect of age and cigarette smoking on markers of platelet activation and PMA. Exclusion criteria in both patients and controls included other inflammatory and prothrombotic conditions to differentiate between the effects of COPD on platelet activation and those of comorbid conditions known to influence platelet function. In the present study, CRP (measured by a rapid latex agglutination test) was negatively correlated with PMA level. On comparing PMA levels among different groups, the results revealed that PMA levels were increased in patients with stable COPD compared with controls. Moreover, PMA was further increased in patients with COPD suffering from acute exacerbation. Taken together, these findings suggest that platelet function may be modified as a consequence of COPD. There was an increase in the number of peripheral blood leucocytes and monocytes in patients with COPD compared with control subjects. Also, patients with COPD had higher platelet counts than controls although levels remained within the normal range. Thus, in comparison with controls, patients with COPD not only have greater platelet activation but also increased numbers of platelets, and both may increase cardiovascular risk. Although there was an increase in platelet and monocyte counts, there was no correlation with PMA which significes the importance of the assessment of PMA irrespective of peripheral blood platelet and monocyte counts.