IL-37 Isoform A Prevents Collagen-Induced Arthritis in Mice by Modulating the Th17/Treg Balance via IL1R8 Receptors

Cytokines play a complex and pivotal role in modulating synovitis in rheumatoid arthritis. Interleukin (IL)-37 is known for its extensive anti-inflammatory properties that set it apart from the majority of other IL-1 family members. However, IL-37a, a member of the IL-37 family, lacks research into rheumatoid arthritis. This research aims to explore the role of IL-37a in regulating T-cell homeostasis in rheumatoid arthritis using the Collagen-Induced Arthritis(CIA) model. IL-37atg mice, a genetically altered strain carrying the human <i>IL-37a</i> gene, were used to test the influence of this cytokine on the progression of arthritis. The results show that IL-37atg mice demonstrated a notable reduction in both the incidence and severity of arthritis relative to WT mice. The protective effect was accompanied by lower levels of cytokines in plasma and synovial tissues (such as IL-17A and IL1β) that drive the inflammatory response. The ratio of Th17/Treg decreased in the lymph nodes of IL-37atg mice. However, the knockout of <i>IL1R8</i> in IL37atg mice eliminated the effects of IL-37a. Additionally, transcriptomic analysis revealed that Th17 cell differentiation is a key pathway through which IL-37a exerts its protective effects, and experiments confirmed that IL-37a suppresses Th17-polarizing in vitro.