Platelet-leukocyte interplay during vascular disease

Vascular disease is a progressive inflammatory condition fuelled by an unhealthy lifestyle of physical inactivity, cholesterol-rich diet, and smoking. Together with endogenous factors such as age, gender, and autoimmune status, an unhealthy lifestyle fosters a pro-inflammatory and pro-thrombotic milieu, which can lead to endothelial dysfunction, atherosclerotic plaque formation and vascular obstruction or degradation of the subendothelial matrix. Platelet-leukocyte interplay represents an important feature in this context. Platelets get activated in a pro-inflammatory and pro-thrombotic microenvironment and readily interact with innate and adaptive immune cells alike. Even though platelet affinity for physical cell-cell contact is highest with monocytes/macrophages and neutrophils, platelets also avidly interact with lymphocytes by soluble mediators. Platelet-leukocyte crosstalk regulates essential immune responses, supporting leukocyte recruitment at sites of vascular insult, promoting proliferation and differentiation of leukocytes and enhancing pro-inflammatory effector functions such as cytokine and reactive oxygen production. However, under certain conditions platelet-leukocyte interplay also dampens the inflammatory process. Crosstalk of platelet and leukocytes thus represents a driving force in vascular disease. In this review, we highlight the impact of various risk factors for vascular disease on platelet-leukocyte interactions and discuss the underlying mechanisms of platelet-mediated changes in immune responses and the effect of immune cells on the haemostatic system. As the underlying pathologies differ between vascular diseases, we summarize our current knowledge on platelet-leukocyte interplay in chronic vascular diseases such as abdominal aortic aneurysm, peripheral and coronary artery disease as well as acute vascular diseases such as ischaemic stroke and venous thromboembolism.