CD27 and granulomatosis with polyangiitis: In the abovementioned study by von Borstel et al, the researchers demonstrated an increased frequency of CD27 + CD38hi B cells in the kidney and urine, but not in the circulation, of GPA patients with active renal involvement, while patients without active renal involvement did not present with B cells in the urine, indicating that CD27 + CD38hi B cells migrated from the circulation to the inflamed kidney.