Evaluation of urinary factor H excretion in patients with idiopathic membranous nephropathy

Background: The complement system plays an important role in renal pathogenesis, and C5b-9, a terminal complement complex, is regarded as the principal mediator of proteinuria in idiopathic membranous nephropathy (MN). Since factor H regulates complement activation at the C3 step and is a crucial factor in complement-mediated tissue injury, the urinary excretion of factor H in patients with idiopathic MN was investigated. Methods: Seven patients with biopsy-proven idiopathic MN were studied for twenty-four weeks. Urinary factor H levels were measured by ELISA from regularly collected urine samples, and then evaluated and compared with assays of urinary protein and C5b-9 excretion. Results: During the study, five patients were treated with steroid therapy. All seven patients maintained stable renal function and showed a decline in urinary protein excretion. The mean level of urinary factor H was markedly elevated (156.1±47.1U/mg U-Cr) before treatment (0 week), and gradually declined to 127.2±43.5U/mg U-Cr at 12 weeks, and to 64.7±26.9U/mg U-Cr) at 24 weeks. This followed decreases in urinary protein and urinary C5b-9 excretion. Percent change in urinary factor H level significantly decreased 24 weeks after treatment without affecting the plasma factor H level. Conclusion: These results suggest that factor H contributes to the regulatory mechanism of in situ complement activation, and thus the study of urinary factor H levels, as well as urinary C5b-9, may be significant in idiopathic MN.