A 5-year-old with systemic juvenile idiopathic arthritis presents with new-onset unremitting fever, hepatosplenomegaly, and confusion. Labs show thrombocytopenia, elevated aspartate transaminase, and hyperferritinemia. The erythrocyte sedimentation rate has paradoxically decreased. In addition to high-dose intravenous glucocorticoids, which targeted therapy is most appropriate for the emergency management of this condition?