Additionally, systemic complement activation stigmas are observed with increased plasma and urine levels of C3a, C5a, and soluble C5b-9, increased plasma levels of Bb (but not C4d) and decreased plasma levels of properdin in AAV patients with active disease, in comparison to those in remission and healthy controls [13,14]. Here, C5AR1 is linked to anti-neutrophil cytoplasmic antibody-associated vasculitis.