Background/Purpose: Enhanced evidence supports that autoimmune diseases often result from an imbalance between regulatory T cells (Tregs) and interleukin-17-producing T helper (Th17) cells. However, under inflammatory arthritic conditions, natural Treg cells (nTregs) lose Foxp3 expression and undergo transdifferentiation into Th17 cells, which has a key role in the pathogenesis of autoimmune arthritis. Our previous data showed that induced iTregs are able to alleviate collagen-induced arthritis(CIA), which inspired us to study the characteristics and functional difference between nTreg and iTreg especially their interaction with inflamed synovial fibroblast cells (ISFs), since ISFs are the most prominent player in both inflammation and joint destruction in rheumatoid arthritis.

Methods: To determine the stability of iTregs or nTregs in the present of ISFs isolated from CIA mice, iTregs or nTregs were co-cultured with ISFs and the expression of Foxp3 and IL-17a was detected by flow cytometry. We also pretreated nTreg and iTreg with ISFs and then compared their suppressive activities against effector T cells. Additionally, iTregs and nTregs were co-cultured with ISFs, and the production of the pro-inflammatory factors TNF-α, IL-6, IL-12, IL-18, IL-1β, IL-11, IL-15 , MCP-1, MMPs, as well as anti-inflammatory cytokines IL-10, IL-1R by ISFs were measured by qPCR, the tumor-like biologic behaviors of ISFs were detected by CCK-8 (proliferation) or crystal violet staining (migration and invasion). To determine the function of nTreg and iTregs on ISFs in CIA mice, ISFs isolated from CIA mice treated with nTregs or iTregs were also subjected to detect the expression of the pro-inflammatory factors and observe their tumor-like biologic behaviors. Finally, we also treated colitis mice with nTregs or iTregs that had been pretreated with or without ISFs to determine their difference in treating an inflammatory disease.

Results: iTregs are more stable functional in the presence of ISFs relative to nTregs. iTreg maintained most Foxp3 and less are converted into Th1 and/or Th17 cells when explored with ISFs. Moreover, ISFs treated with iTregs but not nTregs show reduced expression of pro-inflammatory factors and matrix metalloproteinases and suppressed tumor-like biologic behaviors, with lower proliferation, migration and invasion. In line with results in vitro, infusion of iTregs are more functional to reduce the activation of osteoclasts and bone erosion in CIA mice. ISFs isolated from CIA treated with iTregs also showed reduced expression of pro-inflammatory factors and matrix metalloproteinases and suppressed tumor-like biologic behaviors when compared to treated with nTregs. Adoptive transfer of iTregs that had been pretreated with ISFs are still able to alleviate colitis, while nTreg lost the therapeutic effects on colitis although they are effective if they are not pretreated with ISFs.

Conclusion: iTregs could be more stable and functional than nTregs in the environment of inflammatory synovial tissues in autimmune arthritis. The manipulation of iTreg therapy may provide an advantage strategy in treating patients with rheumatoid arthritis in the future.  

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/difference-of-induced-cd4-and-natural-regulatory-t-cells-in-targeting-inflamed-synovial-tissues-in-autoimmune-arthritis/