Background/Purpose: Microscopic polyangiitis (MPA) is the most common anti-neutrophil cytoplasmic antibodies(ANCA) associated small-vessel vasculitis with specificity of the ANCA to myeloperoxidase(MPO) of neutrophils. MPA mainly affects kidneys and lungs. The kidneys are the most commonly affected organ; and kidney vasculitis can result in renal failure. The interplay of ANCA, neutrophil and complement activation has been implicated in the pathogenesis of MPA. In this study, we tried to establish the relationship of complement activation and the disease activity of MPA and to identify potential biomarkers for this disease.
Methods: Blood samples were collected from 45 MPO-ANCA positive patients who had clinical diagnosis of MPA in People’s Hospital, Peking University, after informed consent. The samples, according to serum C3 levels, were divided into two groups: normal C3 group: ≥0.8 g/L (n=18) and low C3 group: C3<0.8 g/L (n=27). Inflammatory markers (i.e. ESR, CRP), renal functional markers (i.e. BUN, creatinine, 24-hour urinary protein level), and lung diseases were evaluated in the two groups. Birmingham Vasculitis Activity Score-version 3 (BVAS[V3]) was calculated. Data was analyzed using corresponding t test, chi-square test, linear correlation analysis and binary logistic regression, respectively.
Results: We found that: 1) Compared with normal C3 group, low C3 group had significantly lowered C4 (0.17±0.08 g/L vs 0.25±0.08 g/L) but significantly increased CRP (101±57 mg/L vs 33±33 mg/L), 24-hour urinary protein (1.4±1.3g/d vs 0.6±0.5g/d), BUN (17.08±9.02 mmol/L vs 8.62±5.28 mmol/L) and BVAS(V3) (21.4±3.6 vs 15.4±3.8). 2) BVAS(V3) has a significant linear correlation with serum complement C3 level (R2=0.43, P<0.01). 3) Morbidity of severe lung injury (i.e. interstitial lung disease, pneumorrhagia) in low C3 group was higher than that in normal C3 group (92.6% vs 33.3%, X2=17.69, P<0.01). 4) C3, CRP and ESR levels were closely related to the occurrence of severe lung injury, and the logistic regression equation was: P(y)=1/(1+e-2.1+7.54×C3-0.054×CRP-0.027×ESR), in which the overall correct percentage was 93.3%.
Conclusion: Serum complement C3 levels were associated with the disease activity and clinical manifestations of MPA. Therefore, serum C3 level may represent as a biomarker for disease activity and an indicator for organ injury of MPA.
Disclosure:
D. Liu,
None;
J. S. Zhou,
None;
Q. P. Chen,
None;
C. Y. Duan,
None;
L. Wang,
None;
Y. Jia,
None;
K. Li,
None.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/c3-activation-is-associated-with-the-disease-activity-of-microscopic-polyangiitis/