Study to Evaluate the Safety and Tolerability of Two Doses of Rilonacept in Pediatric Subjects With Active Systemic Juvenile Idiopathic Arthritis (SJIA)

Inclusion Criteria include, but are not limited to, the following: * Patients aged 4 to less than 21 years who meet the criteria for active SJIA * Must have been on a stable dose of non-steroidal anti-inflammatory drugs (NSAIDs) for at least 4 weeks prior to the screening visit Exclusion Criteria include, but are not limited to, the following: * Use of certain medications prior to the baseline visit * History of recurrent infections