Immunohistochemical analysis of C4d depositions was performed on kidney biopsies from seven patients with active AAV and kidney involvement (αPR3-ANCA positive GPA, n = 5; αMPO-ANCA positive MPA, n = 2) with median (IQR) eGFR of 30 (21–87) mL/min/1.73 m2. Here, ATRAID is linked to microscopic polyangiitis.