Abstract
Objective: Interleukin-35 (IL-35) is a heterodimeric member of the IL-12 family consisting of p35/IL-12a and EBI3/IL-27b subunits. Expressed in murine Treg cells, IL-35 controls inflammatory diseases in mouse models.
However, human IL-35 is expressed in Teff cells rather than in Treg cells and is shown to be upregulated under inflammatory conditions. Our aim was to examine the involvement of IL-35 in the pathogenesis of rheumatoid arthritis (RA).
Methods: Immunohistochemical and immunofluorescence analysis was used to determine the expression and localization of IL-35 and its subunits (p35/EBI3) and IL-35 receptor (IL12R beta 2/gp130) in RA, osteoarthritis (OA) and psoriatic arthritis (PsA) synovial tissues. Expression of p35/EBI3 subunits and release of inflammatory cytokines upon stimulation with IL-35 were assessed in RA synovial fibroblasts (SFs) and peripheral blood mononuclear cells (PBMCs).
Results: Both IL-35 and its subunits were upregulated in RA in comparison with OA or PsA synovium. Using cell-specific markers, p35 and EBI3 were identified in macrophages, dendritic cells, SFs, and T as well as B cells in RA synovium.
Both p35 and EBI3 were induced by TNF alpha, in RASFs and PBMCs. IL-35 dose-dependently upregulated release of pro-inflammatory mediators IL-1 beta, IL-6 and MCP-1 in PBMCs.
While gp130 receptor subunit was upregulated in RA synovium and was expressed in RASFs and PBMCs, there was no difference in IL12R beta 2 expression subunit among tissues and its presence in RASFs was lacking. Conclusion: Upregulation of IL-35 at sites of inflammation in RA and its pro-inflammatory potential suggests that IL-35 might play an important role in RA pathogenesis.