Figure 3C demonstrates plasma cell infiltration in the kidneys of four active GPA patients. For two of these patients, the urinary CD27+CD38hi B cell frequency was determined and this frequency was increased compared to the circulation (Figure 3B). These findings might indicate that CD27+CD38hi B cells migrate from the circulation to inflamed kidneys during active disease. Here, CD27 is linked to granulomatosis with polyangiitis.