Background/Purpose

Flip (CFLAR) has been identified as a rheumatoid arthritis (RA) risk allele and is important in preventing death receptor mediated apoptosis of dendritic cells (DCs). To examine the in vivorole of Flip in DCs in maintaining immune homeostasis, mice deficient in Flip in conventional DCs were generated (DC-Flip-KO).  The DC-Flip-KO mice spontaneously develop erosive, inflammatory peripheral arthritis, resembling rheumatoid arthritis (RA). These studies were conducted to define the mechanisms that contribute to the development of arthritis in these mice.  

Methods

Immune cell phenotyping was performed by flow cytometry.  DC function was examined by antigen presentation and T regulatory cell (Treg) induction.  Thymic T cell development, selection and tolerance were examined. T cell autoreactivity was determined by the syngeneic mixed lymphocyte response in vitro and by adoptive transfer in vivo, monitored by dilution of CFSE labelled T cells. Treg function was examined by suppression of CD4⁺ T cell proliferation.  Autoantibodies to joint components were identified by immunoblotting. DC-Flip-KO mice were crossed with Rag^-/- to generate DC-Flip-KO-Rag^-/-double mutant lines and arthritis was evaluated.  All data are analyzed comparing indicated genotypes in age and gender matched groups.

Results

CD11c-cre mediated Flip deficiency resulted in consistent reduction of the CD11c⁺CD8α⁺ subset of DCs in central and peripheral lymphoid organs before or after the onset of arthritis. No defects in thymic central tolerance were identified, however, increased autoreactive CD4⁺ T cells and plasmablasts are identified in the lymph nodes draining the inflamed joints, and both were positively correlated with the severity of arthritis.  The DC-Flip-KO mice possessed autoantibodies specific for joint components.  Further, Tregs were reduced in the thymus and spleen of DC-Flip-KO mice in a setting of lymphopenia.  In addition, the number of Tregs in the spleen inversely correlated with the severity of the arthritis and adoptive transfer of Tregs ameliorated joint inflammation.  DCs isolated from the DC-Flip-KO mice effectively presented antigen but were deficient in promoting the induction of Tregs. Supporting the role of T and B cells, DC-Flip-KO-Rag^-/- mice, which lack of both T and B cells, develop significantly milder and self-resolving arthritis compared with the DC-Flip-KO-Rag^+/-mice. 

Conclusion

Flip plays a key role in the survival of the CD8α⁺CD11c⁺ DC subset in vivo. The loss of this subset impairs the generation and/or maintenance of Tregs, which in turn permits the expansion of antoreactive CD4⁺T cells and autoantibody producing B cells, resulting in autoimmune arthritis. Our observations suggest that the DC-Flip-KO mouse is a novel model of RA that may provide important insights and permit in depth interrogation of the pathogenesis of RA.

---

« Back to 2014 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/flip-deficiency-in-dendritic-cells-promotes-spontaneous-arthritis-mediated-by-reduced-treg-and-increased-autoreactive-cd4t-cells/