MPO and granulomatosis with polyangiitis: Recent work from clinical cohorts has also shown significant differences in circulating IL-6 between patients with GPA and patients with MPA, supporting our findings that IL-6 is a key cytokine in mediating MGC and granuloma formation in patients with GPA.40 We confirmed a role of PR3 in mediating MGC even in patients with MPO-ANCA GPA, suggesting that certain cellular characteristics predispose to MGC formation in GPA, the subject of ongoing work.