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Complement system activation is associated with spinal radiographic progression in axial spondyloarthritis after 2
Clara Mistegaard1,2,3, Anne Troldborg1,2,3, Murat Torgutalp4
1Department of Rheumatology, Aarhus University Hospital, Aarhus, Denmark.
Objective:
To investigate complement system activation and complement protein levels in relation to radiographic progression in axial spondyloarthritis (axSpA) within a longitudinal randomised controlled trial (RCT) of radiographic axSpA patients initiating tumour necrosis factor inhibitor (TNFi) therapy.
Methods:
Serum samples from 96 patients with active radiographic axSpA in the multicentre RCT CONSUL were analysed by immunoassays for complement activation, that is, C3dg and complement proteins (MBL, CL-L1, M-, H- and L-ficolin; MASP-1,-2 and -3; and MAp44) before and after 108 weeks of TNF inhibitor therapy with golimumab.
Results:
Baseline serum levels of total complement activation, that is, C3dg and lectin pathway activating protease MASP-1 were elevated in patients with new bone formation (new syndesmophytes and/or growth of existing syndesmophytes) after 2 years of follow-up, whereas baseline MASP-3 levels were decreased. Assessed by univariate logistic regression, baseline levels of MASP-1, MASP-3 and C3dg were associated with the development of new bone formation and remained significant in a corresponding multivariate logistic regression analysis. At follow-up, serum levels of C3dg and complement lectin pathway initiator L-ficolin were elevated in patients with new bone formation, and C3dg remained significant in a corresponding multivariate logistic regression analysis.
Conclusions:
Complement activation marker C3dg, MASP-1 and MASP-3 levels before TNFi therapy predicted new bone formation after 2 years of follow-up among axSpA patients with a high risk of radiographic progression. Furthermore, levels of L-ficolin and C3dg at follow-up were elevated in axSpA patients with new bone formation. Our findings support an association between activation of the complement system and radiographic spinal progression in patients with axSpA.
