IL6 and Castleman disease: IL-6 is well established as a valuable clinical target, and antibodies that block either IL-6 (e.g., siltuximab) or IL-6R (e.g., tocilizumab or sarilumab) are routinely used for treatment of inflammatory arthritis, juvenile idiopathic arthritis, multi-centric Castleman disease, cytokine release syndrome (commonly encountered in the setting of tumor immunotherapy), and giant cell arteritis (212–217).