If a participant experiences a first flare after initial response, participants in the Step-Up group will start prednisolone treatment at the last effective dose (i.e., participants that previously responded to prednisolone 40 mg/day will receive a dose of 40 mg/day for at least 3 days and up to 2 weeks; participants that previously responded to prednisolone 1 mg/kg/day will receive a dose of 1 mg/kg/day for a minimum of 7 days and up to 2 weeks). If the last effective dose was 40 mg/day and the participant does not respond within 14 days, the dose will be adjusted to 1 mg/kg/day for a minimum of 7 days and up to 2 weeks. In case the participant does not respond to prednisolone (i.e., does not return to their individual baseline partial Mayo score obtained at study Week 4), the participant will enter Level 3 and receive treatment with IV infliximab.