Background Interleukin 35 (IL-35) is a recently identified member of the IL-12 family of cytokines and represents a novel target for therapies of autoimmune, inflammatory, and infectious diseases, including rheumatoid arthritis (RA).^{Choi et al. 2015}

IL-35 is a heterodimer consisting of EBV-induced gene 3 (EBI3) and IL-12α chain p35 (Nakano et al. 2015). In contrast to other IL-12 cytokine family members, IL-35 appears to have anti-inflammatory and immunosuppressive properties mediated by induction of regulatory T and B cells; (Choi et al. 2015. Huang et al. 2017). In particular, IL-35 may play an important role in suppressing the inflammatory response by expanding regulatory T cells and in dampening the differentiation of Th17 cells (Niedbala et al. 2007).

Objectives This study was designed to analyse effects of IL-35 on stimulated peripheral blood mononuclear cells (PBMC) and their subpopulations in RA patients and healthy controls.

Methods PBMCs of 10 RA patients and 10 controls as well as CD14 +and CD4+cells isolated from PBMCs using magnetic separation were cultured for 24 hours, and subjected to three conditions: no stimulation, stimulation with LPS (PBMC and CD14+) or stimulation with anti-CD3/anti-CD28 antibodies (PBMC and CD4+), and stimulation with added IL-35 (100 ng/ml). A panel of nine cytokines (IL-1β, IL-6, IL-8, IL-10, IL-12 (p70), IL-17a, IFN-γ, MIP-1β and TNF) was analysed in the cell culture supernatants.

Results RA patients had higher serum levels of IL-35 compared to healthy controls. A decreased secretion of IL-8 and increased secretion of TNF in the presence of IL-35 was observed in vitro in stimulated PBMCs of RA patients. In the control group, we observed an increased secretion of IL-6 by PBMCs and decreased secretion of IL-10 by T lymphocytes as a result of IL-35 addition to stimulated cells.

Conclusions In this study, we found elevated serum levels of IL-35 in RA patients suggesting a possible involvement of IL-35 in the pathogenesis of RA. However, in vitro, the effect of IL-35 on stimulated immune cells was partially anti-inflammatory and partially pro-inflammatory, suggesting that the effect of IL-35 is pleiotropic and depends on the type and the state of the affected immune cell.

References [1] Huang A, Cheng L, He M, et al. Interleukin-35 on B cell and T cell induction and regulation. J. Inflamm. (United Kingdom)2017;14.

[2] Choi J, Leung PSC, Bowlus C, Gershwin ME. IL-35 and Autoimmunity: a Comprehensive Perspective. Clin Rev Allergy Immunol2015;49:327–332. doi:10.1007/s12016-015-8468-9

[3] Nakano S, Morimoto S, Suzuki S, et al. Immunoregulatory role of IL-35 in T cells of patients with rheumatoid arthritis. Rheumatology (Oxford)2015;54:1498–1506. doi:10.1093/rheumatology/keu528

[4] Niedbala W, Wei XQ, Cai B, et al. IL-35 is a novel cytokine with therapeutic effects against collagen-induced arthritis through the expansion of regulatory T cells and suppression of Th17 cells. Eur J Immunol2007;37:3021–3029. doi:10.1002/eji.200737810

Acknowledgements Grant support: APVV-15–0228 and VEGA 2/0161/16

Disclosure of Interest None declared