Background/Purpose:

Recently, it has been reported that interleukin (IL)-27 treatment reduces inflammation and ameliorates arthritis in collagen-induced arthritis mice. IL-27 is a heterodimeric cytokine composed of IL-27p28, which is similar to IL-6, and EBI3, which is similar to soluble IL-6 receptor (sIL-6R). Notably, each subunit is produced independently, allowing IL-27 to associate with other proteins. sIL-6R is highly concentrated in serum from patients with rheumatoid arthritis (RA). We elucidated the role of sIL-6R in regulating IL-27 signaling.

Methods:

Surface Plasmon Resonance analysis was used to examine the binding of IL-27 to sIL-6R. Competitive ELISA was performed to evaluate the binding to IL-27p28 and the dissociation of EBI3 from IL-27p28 in the presence of sIL-6R. CD14⁺ cells were isolated from peripheral blood mononuclear cells of healthy subjects. CD14⁺ cells were incubated with IL-27 and sIL-6R for 20 minutes, and phosphorylation of STAT3 was measured by FACS. CD14⁺ cells were incubated with M-CSF, TNF-α, IL-27 and sIL-6R for 48 hours, and MCP-1 production from CD14⁺ cells was measured by ELISA. CD14⁺ cells were cultured with RANKL and M-CSF in the presence of IL-27 and sIL-6R for 4 days, and the number of osteoclasts was counted after tartrate-resistant acid phosphatise (TRAP) staining. Concentrations of IL-27p28/sIL-6R complex and IL-27p28/EBI3 complex in serum from healthy subjects and those with RA were determined by ELISA.

Results:

Surface Plasmon Resonance analysis showed that binding curves were generated from experiments in which IL-27 was exposed to a high-density of sIL-6R coated on a sensor chip. sIL-6R promoted the dissociation of EBI3 from IL-27p28 and the formation of IL-27p28/sIL-6R complex in a dose-dependent manner. Anti-IL-6 receptor antibody (tocilizumab) inhibited the formation of IL-27p28/sIL-6R complex. To examine the effect of sIL-6R on IL-27 signaling, we measured phosphorylation of STAT3, which is increased by IL-27, after stimulating sIL-6R and IL-27, and found that sIL-6R decreased phosphorylation of STAT3. Next, we examined whether sIL-6R inhibited the IL-27-mediated anti-arthritic effect. Whereas IL-27 reduced TNF-α-induced MCP-1 production from CD14⁺ cells, IL-27 did not decrease TNF-α-induced MCP-1 production in the presence of sIL-6R. Similarly, RANKL-mediated osteoclast formation was inhibited by IL-27 but was not inhibited by IL-27 in the presence of sIL-6R. Finally, we examined whether IL-27p28/sIL-6R complex was formed in serum from healthy subjects and from those with RA. Surprisingly, IL-27p28/sIL-6R complex in RA serum was significantly higher than that in healthy serum.

Conclusion:

We elucidated that sIL-6R binds to IL-27p28, antagonizes IL-27 signaling, and blocks IL-27-mediated anti-arthritic effect. In addition, we showed that IL-27p28/sIL-6R complex was more abundant in serum from RA patients than in that from healthy subjects. These data suggest that sIL-6R may be involved in regulating the IL-27 function in RA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-role-for-soluble-interleukin-6-receptor-as-an-antagonist-of-interleukin-27-signaling/