<qa>  What is the main cause of proliferative glomerulonephritis?Proliferative glomerulonephritis is a common and severe manifestation of systemic lupus erythematosus SLE that usually requires intensive therapy with high doses of glucocorticosteroids and cytotoxic drugs, such as intravenous IV cyclophosphamide CYC. The objective of the MAINTAIN Nephritis Trial is to compare mycophenolate mofetil MMF and azathioprine AZA, in terms of efficacy and toxicity, as remission-maintaining treatment of proliferative lupus glomerulonephritis, after a remission-inducing therapy with a short-course IV CYC regimen. The hypothesis addressed by the MAINTAIN Nephritis Trial is that MMF is superior to AZA. 