Reestablishing immune tolerance and long term suppression 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) in vitro. However the molecular mechanism of RA pDC-mediated Treg induction remains elusive. Herein, we sought to identify novel targets of RA pDCs that contributes to the induction of tolerance and might lead to remission.Materials/methods
pDCs were isolated from peripheral blood of RA patients responding to anti-TNF therapy (remission based on disease activity score DAS28 <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 pDCs. Finally, in vitro cultures of pDCs activated with CpG B were performed to assess the functional importance of these gene signatures.Results
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. We verified these results using flow cytometry for the surface expression levels of IL-6 receptor in a subsequent cohort of patients responding to therapy (n=3) vs healthy. Moreover, in functional experiments assessing IL-6R activation, coculture of healthy pDCs with CpG B in the presence or absence of recombinant IL-6, revealed that pSTAT3 levels were increased in pDCs cultured in the presence of IL-6. Cytokine expression studies (IFN-α, β, TNF-α, IL-6) are in progress to address the role of pDCs upon IL-6 signalling. The functional importance of the previous findings will be addressed in coculture experiments of IL-6 stimulated pDCs with CD4+CD25- T cells isolated from cord blood and monitor T cell proliferation based on dilution of CFSE staining.Conclusions
We found that pDCs from RA patients in remission display increased IL-6R expression levels and IL-6 signalling pathway is induced in healthy pDCs in the presence of IL-6. This novel finding that may drive pDCs towards a previously described tolerogenic phenotype, need to be further addressed.