Severe leptospirosis is frequently complicated by a hemorrhagic diathesis, of which the pathogenesis is still largely unknown. Thrombocytopenia is common, but often not to the degree that spontaneous bleeding is expected. We hypothesized that the hemorrhagic complications are not only related to thrombocytopenia, but also to platelet dysfunction, and that increased binding of von Willebrand factor (VWF) to platelets is involved in both platelet dysfunction and increased platelet clearance.
A prospective study was carried out in Semarang, Indonesia, enrolling 33 hospitalized patients with probable leptospirosis, of whom 15 developed clinical bleeding, and 25 healthy controls. Platelet activation and reactivity were determined using flow cytometry by measuring the expression of P-selectin and activation of the α IIbβ 3 integrin by the binding of fibrinogen in unstimulated samples and after ex vivo stimulation by the platelet agonists adenosine-diphosphate (ADP) and thrombin-receptor activating peptide (TRAP). Platelet-VWF binding, before and after VWF stimulation by ristocetin, as well as plasma levels of VWF, active VWF, the VWF-inactivating enzyme ADAMTS13, thrombin-antithrombin complexes (TAT) and P-selectin were also measured. Bleeding complications were graded using the WHO bleeding scale. Our study revealed that platelet activation, with a secondary platelet dysfunction, is a feature of patients with probable leptospirosis, especially in those with bleeding manifestations. There was a significant inverse correlation of bleeding score with TRAP-stimulated P-selectin and platelet-fibrinogen binding (R = -0.72, P = 0.003 and R = -0.66, P = 0.01, respectively) but not with platelet count. Patients with bleeding also had a significantly higher platelet-VWF binding. Platelet counts were inversely correlated with platelet-VWF binding (R = -0.74; P = 0.0009. There were no correlations between platelet-VWF binding and the degree of platelet dysfunction, suggesting that increased platelet-VWF binding does not directly interfere with the platelet α IIbβ 3 signaling pathway in patients with probable leptospirosis.
Bleeding is a frequent complication of leptospirosis, a disease caused by the pathogenic spirochaete Leptospira. Although thrombocytopenia is common, studies have shown that it does not fully explain the bleeding events seen in these patients. We hypothesized that platelet dysfunction plays a role in the development of bleeding complications. The present study involved 33 hospitalized patients with probable leptospirosis and 25 healthy controls. We report that circulating platelets from patients with severe, probable leptospirosis were activated, but less reactive to ex vivo activation. The degree of this platelet dysfunction was associated with bleeding, in contrast to the degree of thrombocytopenia. Platelets of leptospirosis patients also demonstrated increased binding with von Willebrand factor (VWF), and a strong negative correlation with platelet count suggesting that this binding is important for platelet clearance.