This study investigated the effect of mycophenolate mofetil and cyclosphosphamide on lymphocyte subsets in patients with proliferative lupus nephritis. Patients with biopsy-proven Class III/IV+/-V LN were randomized to received: 1) prednisolone (0.8mg/kg/day) plus CTX (1.5-2mg/kg/d) for 6 months) followed by Azathioprine (AZA) (1-1.5mg/kg/d) maintenance; OR 2) prednisolone (0.8mg/kg/d) plus MMF (1g bd) for 6 months, followed by MMF (tapered according to clinical status) as maintenance. The lymphocyte subsets and serum cytokine profiles will be measured at 4-, 12-, and 24-, 36- and 48 weeks after induction treatment. The lymphocyte subsets and serum cytokine profiles will be compared between the two treatment regimens, and also correlated with subsequent risk of relapse.