Detection of Free and Olokizumab-Bound Interleukin-6 during Anticytokine Therapy

Abstract Elevated systemic production of interleukin-6 (IL-6) is associated with a broad spectrum of autoimmune and inflammatory diseases. Monoclonal antibody therapies targeting IL-6 or its receptor are widely used to neutralize the accompanying adverse effects. This study addresses the challenge of independently quantifying free and olokizumab (OKZ)-bound IL-6 in biological samples using a preclinical mouse model with regulated overexpression of human IL-6. We developed an enzyme-linked immunosorbent assay (ELISA), in which biotin-labeled OKZ served as a detecting agent, enabling in vivo tracking of dynamics of IL-6/OKZ immune complexes. OKZ effectively reduced free IL-6 levels in mice with cytokine overexpression for at least 7 days, while persisting in circulation as IL-6/OKZ complexes. Additionally, we assessed the kinetics of neutralizing anti-OKZ antibody formation in this preclinical model. The methods developed can be applied for clinical monitoring during anti-cytokine therapy and in preclinical studies using mouse models to evaluate the efficacy of such therapy in controlling IL-6-dependent inflammation in experimentally induced diseases.