Hypocomplementemia dynamics during tocilizumab therapy in systemic juvenile idiopathic arthritis: a retrospective longitudinal study

Complement C3 and C4 levels during TCZ treatment follow a trajectory characterized by a rapid early decline followed by a sustained low-level plateau. Long-term hypocomplementemia appears to be well tolerated, with no increased risk of serious infections or autoimmune complications. These findings suggest that hypocomplementemia reflects deep IL-6 signaling inhibition rather than pathological complement consumption.