Efficacy of Intravenous Cyclophosphamide Pulse Therapy for P-Glycoprotein-expressing B Cell-associated Active True Renal Lupus Vasculitis in Lupus Nephritis

True renal lupus vasculitis (TRLV), a vascular lesion usually associated with proliferative lupus nephritis (LN), is resistant to conventional treatments. The expression of P-glycoprotein (P-gp) on activated lymphocytes causes drug resistance. We herein report a patient with TRLV, minimal change LN, overexpression of P-gp on peripheral B cells, and accumulation of P-gp(+) B cells at the site of TRLV. High-dose corticosteroids combined with intravenous cyclophosphamide pulse therapy resulted in clinical remission and the long-term normal renal function.