Intractable membranous lupus nephritis showing selective improvement of subepithelial deposits with tacrolimus therapy: a case report

A 37-year-old female patient was admitted for evaluation of nephrotic proteinuria refractory to prednisolone and other immunosuppressants in 2004. On admission, urinary protein loss was 16 g/d. Anti-ds DNA antibody was positive and hypocomplementemia was detected. Renal biopsy revealed membranous lupus nephritis. Because 5 cyclophosphamide pulse therapies did not have an effect, tacrolimus was started at 3 mg daily. Proteinuria decreased to 4.8 g/d after 5 months and was < 0.1 g/d in 2009, but antids DNA antibody remained positive and hypocomplementemia persisted. Repeat renal biopsy revealed thinning of the glomerular capillary walls and disappearance of subepithelial electron-dense deposits. However, the subendothelial and mesangial deposits were unchanged. In this patient, proteinuria refractory to various immunosuppressants including cyclosporine A improved after administration of tacrolimus, and selective disappearance of subepithelial deposits was seen histologically. This is the first histological evidence that tacrolimus therapy may cause removal of subepithelial deposits, which are separated from the circulation by the glomerular basement membrane. This finding is supported by experimental data that tacrolimus selectively block the binding of FK-binding protein 12 to transient receptor potential-cation channel 6, resulting in normalization of affected podocytes.