THU0072 Gene signature of plasmacytoid dendritic cells reveals novel pathways contributing to tolerance in rheumatoid arthritis patients
Authors: G. Papadaki, P. Goutakoli, J.R. Grün, A. Grützkau, A. Fanouriakis, G.A. Pavlopoulos, I. Iliopoulos, G. Bertsias, D. Boumpas, P. Sidiropoulos, P. Verginis
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Reestablishing immune tolerance and long term remission represent major therapeutic goals in rheumatoid arthritis (RA). Our laboratory previously demonstrated that plasmacytoid dendritic cells (pDCs) from RA patients in remission have the ability to induce IL-10 producing regulatory T cells (Tregs) <i>in vitro</i>.<sup>1</sup> However, the molecular pathway of RA pDC-mediated Treg induction remains elusive. <h3>Objectives</h3> Herein, we sought to identify the molecular mechanism through which pDCs contribute to restoration of tolerance in RA. <h3>Methods</h3> pDCs were isolated from peripheral blood of RA patients responding to anti-TNF therapy (remission based on disease activity score DAS28 &lt;5.1) and healthy control subjects and DNA microarrays were performed. Flow cytometry and real time PCR were used to verify the expression of de-regulated genes in RA pDCs. Finally, <i>in vitro</i> cultures of pDCs activated with CpG A in the presence or absence of recombinant IL-6 (rIL-6) were performed to assess the functional importance of these gene signatures. <h3>Results</h3> pDCs from RA patients (n=5) exhibited a differential gene signature (6741 deregulated genes) compared to pDCs from healthy controls (n=5). Notably, IL-6 receptor (IL-6R) gene, exhibited increased expression levels in pDCs isolated from RA patients compared to healthy pDCs and the surface expression levels of IL-6 receptor were verified in a subsequent cohort of patients responding to therapy (n=9) versus active patients or healthy donors. Moreover, assessment of IL-6 signalling pathway in RA patients versus healthy donors revealed a significant increase of pSTAT1 expression levels in RA patients (n=9) compared with healthy donors (n=6) (mean fluorescence intensity ±SEM, 7.98±0.8 versus 12.65±1.18, p value=0.0076). Importantly, IL-6-treated pDCs exhibited a vast decrease in TNF-α production (p value=0.0002) whereas no differences were found in the production of IFN-α and in their antigen presenting capacity between CpG-treated pDCs in the presence or absence of rIL-6. Moreover, confocal experiments in progress will assess the expression levels of TNF-α in pDCs isolated from RA patients in remission versus active or healthy donors. The functional importance of the previous findings will be addressed in coculture experiments of IL-6 stimulated pDCs with monocytes isolated from healthy donors and monitor their activation and maturation status. <h3>Conclusions</h3> We found that pDCs from RA patients in remission display increased IL-6R expression levels and an activated IL-6 signalling pathway. Activation of IL-6 signalling on pDCs <i>in vitro</i> significantly decreases the production of TNF-α whereas it does not alter IFN-α production and their antigen presenting capacity. This novel finding and the underlying mechanism that may drive pDCs towards a previously described tolerogenic phenotype, need to be further addressed. <h3>Reference</h3> [1] Kavousanaki, et al. Arthritis Rheum2010. <h3>Acknowledgements</h3> Project funded by "Pancretia" health organisation. <h3>Disclosure of Interest</h3> None declared