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Review
. 2021 Oct 18:12:764825.
doi: 10.3389/fimmu.2021.764825. eCollection 2021.

Emerging Role of Eosinophils in Resolution of Arthritis

Yi Qin  1 , Hui-Zhi Jin  1 , Yu-Jing Li  2 , Zhu Chen  1
Affiliations
Review

Emerging Role of Eosinophils in Resolution of Arthritis

Yi Qin et al. Front Immunol. .

Abstract

Eosinophils are a minor component of circulating granulocytes, which are classically viewed as end-stage effector cells in host defense against helminth infection and promoting allergic responses. However, a growing body of evidence has emerged showing that eosinophils are versatile leukocytes acting as an orchestrator in the resolution of inflammation. Rheumatoid arthritis (RA) is the most common chronic inflammatory disease characterized by persistent synovitis that hardly resolves spontaneously. Noteworthy, a specific population of eosinophils, that is, regulatory eosinophils (rEos), was identified in the synovium of RA patients, especially in disease remission. Mechanistically, the rEos in the synovium display a unique pro-resolving signature that is distinct from their counterpart in the lung. Herein, we summarize the latest understanding of eosinophils and their emerging role in promoting the resolution of arthritis. This knowledge is crucial to the design of new approaches to rebalancing immune homeostasis in RA, considering that current therapies are centered on inhibiting pro-inflammatory cytokines and mediators rather than fostering the resolution of inflammation.

Keywords: alternatively activated macrophages; eosinophil; innate lymphoid cells; resolution; rheumatoid arthritis.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
The role of ILC2–eosinophil–M2 macrophage axis in promoting resolution of arthritis. In allergen-triggered lung inflammation, ILC2 was expanded and activated in response to stimulators such as IL-33 and IL-25. Systemically elevated IL-5 secreted by ILC2 drives proliferation and recruitment of rEos into the inflamed joints, where they produce a variety of lipid mediators and anti-inflammatory type 2 cytokines, which facilitate M2 macrophage priming and eventually contribute to the resolution of arthritis.
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