Complement activation in ANCA-associated vasculitis

Aim

To study the common and alternative pathway comple- ment components in patients with ANCA-associated vasculi- tis (AAV).

Material and methods

Complement components were evaluated in 59 patients with newly diagnosed or relapsing granulomatosis with polyangiitis or microscopic polyangiitis and 36 healthy volunteers. Only patients with active disease as assessed by Birmigham Vasculitis Activity Score (BVAS) were enrolled in the prospective study.

Results

The median concentrations of the common pathway components C3a, C5a and C5b-9 and the alternative pathway components factor B were higher in active AAV pati- ents than in healthy controls (p<0.001). Achievement of remission was associated with reductions in C3a (p=0.005), C5a (p=0.035), and factor B levels (p=0.045), whereas C5b-9 and properdin levels did not change significantly. In active AAV, complement levels did not depend on ANCA specificity, disease phenotype, previous immunosuppression, or disease severity.

Conclusion

Our findings suggest activation of the com- plement system predominantly via the alternative pathway in AAV patients.

Key words

Complement, ANCA, vasculitis, biomarker, meta-analysis.