Participants from an ongoing observational study (P05319) who have a limited (adequate but less than optimal) response to infliximab will be randomized to either increase the frequency of infliximab infusions from every 8 weeks to every 6 weeks, or to add weekly methotrexate to their current treatment plan. While receiving infliximab study treatment(s), patients in this study will attend regularly scheduled office visits for various clinical tests for safety and effectiveness evaluations.