Diagnostic role of endothelial microparticles in vasculitis

Objective. Endothelial cells play a central pathogenetic role in ANCA-associated small-vessel vasculitis (AAV). Circulating endothelial cells (CECs), as a marker of endothelial damage, have been shown to be elevated in vasculitis. More recently, endothelial microparticles (EMPs) were found to be increased in active childhood vasculitis. The role of EMP in adult AAV and the relationship between EMP and CEC is unclear. Patients and methods. We studied 26 patients with AAV, 12 healthy volunteers and 10 patients with IgA nephropathy as disease control. Platelet-poor plasma was ultracentrifuged. MPs were identified and enumerated with flow cytometry, Annexin V, CD62E and CD105 antibodies. Leucocyte- and platelet-derived MPs were also measured. CEC were isolated and enumerated with CD146-driven immuno-magnetic isolation. Results. EMPs are significantly elevated in patients with active vasculitis (CD62E: mean 248 MP/mu l;+/- 198 s.d.; CD105: 121 +/- 135/mu l) compared with patients in remission/partial remission (CD62E: 55 +/- 30/mu l, P = 0.001; CD105: 16 +/- 12/mu l, P = 0.002) and healthy volunteers (CD62E: 66 +/- 33/mu l, P = 0.002; CD105: 25 +/- 26/mu l, P = 0.007). The MP count correlates with disease activity measured by the Birmingham Vasculitis Activity Score (BVAS) (CD62E: r = 0.703; CD105: r = 0.445, P < 0.023). Conclusion. EMPs are elevated in active adult AAV. EMP levels correlate with disease activity and might serve as a marker of endothelial activation and damage. Differential detection of endothelial, platelet- and leucocyte-derived MPs may provide more insight in to the pathogenesis of AAV.