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

---

Aleksandra V. Pavlova¹, Anna M. Litvinova^1,2,3, Ekaterina O. Gubernatorova^2,3, Anastasia S. Yakovleva^2,3,4, Sergei A. Nedospasov^1,2,3,4, Marina S. Drutskaya^1,2,3,4,a*, and Irina V. Astrakhantseva^1,b*

¹Department of Immunobiology and Biomedicine, Life Sciences and Genetics Center, Sirius University of Science and Technology, 354340 Sochi, Russia

²Laboratory of Molecular Mechanisms of Immunity, Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, 119991 Moscow, Russia

³Center for Precision Genetic Technologies for Medicine, Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, 119991 Moscow, Russia

⁴Faculty of Biology, Lomonosov Moscow State University, 119991 Moscow, Russia

^* To whom correspondence should be addressed.

Received: July 23, 2025; Revised: November 1, 2025; Accepted: November 20, 2025

---

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.

---

KEY WORDS: autoimmune diseases, IL-6-dependent systemic inflammation, enzyme-linked immunosorbent assay, mouse models, IL-6/OKZ complexes

DOI: 10.1134/S0006297925602308

Publisher’s Note. Pleiades Publishing remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

---