Platelets are activated in ANCA-associated vasculitis via thrombin-PARs pathway and can activate the alternative complement pathway

Abstract

BackgroundIn this study, we investigated the mechanism of platelet activation in patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), as well as the activation of the alternative complement pathway by platelets in AAV.MethodsCD62P and platelet-leukocyte aggregates in AAV patients were tested by flow cytometry. Platelets were stimulated by plasma from active AAV patients. The effect of the thrombin-protease-activated receptors (PARs) pathway was evaluated by blocking thrombin or PAR1 antagonists. After platelets were activated by plasma from AAV patients, Ca/Mg-Tyrode’s buffer and Mg-EGTA buffer were used to measure complement activation in liquid phase and on the surface of platelets.ResultsThe levels of CD62P-expressing platelets and platelet-leukocyte aggregates were significantly higher in active AAV patients than those in remission and normal controls. Platelets were activated by plasma from active AAV patients (percentage of CD62P-expressing platelets, 97.7 ± 3% vs. 1 ± 0.2%, p < 0.0001, compared with those incubated with healthy donor plasma), and this was inhibited by thrombin or PAR1 antagonists (percentage of CD62P-expressing platelets, 97.7 ± 3% vs. 2.7 ± 1%, p < 0.0001, 97.7 ± 3% vs. 5 ± 1.4%, p < 0.0001, respectively). Platelets activated by plasma from AAV patients could trigger complement activation via the alternative pathway, as demonstrated by significant elevation of C3a, C5a, and sC5b-9 and significantly more C3c and C5b-9 deposition on the surface of platelets.ConclusionsPlatelets were activated in AAV patients, and such activation was at least partially attributed to the thrombin-PARs pathway. Activated platelets triggered the alternative complement pathway in AAV.

Gene Expression Pathways across Multiple Tissues in Antineutrophil Cytoplasmic Antibody-associated Vasculitis Reveal Core Pathways of Disease Pathology

“…(34,35) Platelets are acute phase reactants, but can also secrete cytokines and mediate inflammatory responses. (36,37) Despite the increased CV risk associated with AAV, at this time there are no specific recommendations for CV risk reduction in these patients.…”

Inflammation as a Driver of Vulvar Squamous Cell Carcinoma Progression.

“…pro-in ammatory proteins, such as high-mobility group box 1 (HMGB1) that was shown to be elevated in AVV patients' sera [55]. In the pathogenesis of GPA, besides neutrophils, the key effector cells (https://clinicaltrials.gov/ct2/show/NCT01862068), also activated platelets are proposed to play an important role [56]. NETs can activate the alternative complement pathway and contribute to thrombus formation while in turn platelets induce NETosis with HMGB1 expression on the platelets mediating the process [54].…”

“…The hrHPV status of tissue samples was determined, as described previously [64], using the AmpliSens® HPV HCR-genotype-titre-FRT kit (InterLabService Ltd.), which detects 14 high risk HPV (hrHPV) genotypes, namely: HPV16, 18,31,33,35,39,45,51,52,56,58,59,66 is the -log (p value). Pathways predicted to be activated are in orange (based on the Z-scores, the activation scores determined by IPA), and grey bars relate to pathways with no activity pattern available.…”

Complement factor H levels in steady state sickle cell anaemia

“…There was also a negative correlation between complement factor H and platelet count although the correlation was not statistically significant. Miao et al describes the role of platelets in immunology through their ability to bind complement proteins, and initiate complement activation (22). The negative correlation between platelet count and complement factor H is an example of the complement activation that overwhelms regulatory mechanisms.…”