In addition to receiving study drug (rituximab or placebo), participants in each treatment group received mycophenolate mofetil at a starting dose of 1500 mg/day IV in 3 divided doses and were titrated up by 500 mg/week to 3000 mg/day by Week 4, as tolerated. Participants in each treatment group also received methylprednisolone 1000 mg IV prior to and 3 days following the first study drug infusion and methylprednisolone 100 mg IV prior to the other study drug infusions. Participants in each treatment group also received diphenhydramine 50 mg orally and acetaminophen 1000 mg orally 30-60 minutes prior to each study drug infusion. From Days 2 to 16, participants in each treatment group received prednisone 0.75 mg/kg/day orally (maximum dose of 60 mg) except on the day of the second methylprednisolone dose. On Day 16, a taper was initiated to achieve a dose of 10 mg/day by Week 16.