Background: Osteopontin is a pleiotropic cytokine involved in the recruitment and retention of neutrophils to sites of inflammation, which are the primary targets cells in antineutrophil cytoplasmic autoantibody-associated vasculitis (AAV). Osteopontin may play a role in the pathogenesis of AAV.
Methods: 24 patients with systemic AAV and six patients with limited granulomatous disease were included. 19 patients were followed up at 6 and 12 months after the initiation of immunosuppressive therapy. 21 matched healthy volunteers and 20 body mass index and glomerular filtration rate-matched patients with IgA nephropathy were included as controls. Plasma levels of osteopontin were measured by ELISA. Disease activity was gauged by the Birmingham vasculitis activity score (BVAS) and C-reactive protein (CRP).
Results: Osteopontin levels are elevated compared with controls (healthy p<0.001; IgA p<0.001).Osteopontin levels decrease significantly during follow-up (p=0.02). Osteopontin levels correlate with disease activity (BVAS r=0.93; CRP r=0.73; all p<0.001) as well as erythrocyturia (r=0.7, p<0.001) and proteinuria (r=0.54, p=0.007).
Conclusions: Active AAV is characterised by increased plasma levels of osteopontin, which decrease dramatically with successful therapy. Osteopontin may mediate the inflammatory process in AAV through the recruitment of neutrophils.