IL-33/ST2 induces Tfh cells activation and GCs formation in collagen-induced arthritis

The Interleukin-33 (IL-33) has a strong[AL1] pro-inflammatory effect on collagen-induce arthritis (CIA), a classic animal model of rheumatoid arthritis (RA). However, the underlying mechanism remains unclear. In this study, we investigated the presence of the IL-33 receptor suppression of tumorigenicity 2 (ST2) on T follicular helper (Tfh) cells and its impact on CIA through regulation of Tfh cells and germinal center (GC) B cells. [AL1]LE: Please check if the corresponding author's telecommunications data are correctly captured/indicated.

In vitro studies involved treating polarized Tfh cells with IL-33 to analyze its effects on Tfh differentiation by measuring ST2, PD-1, and CXCR5 expression using flow cytometry. C57BL/6J mice were immunized with keyhole limpet hemocyanin (KLH) and divided into three groups: control, KLH-only, and KLH+IL-33. Additionally, ST2^-/^- mice were immunized with KLH. The ratio of T follicular regulatory (Tfr)/Tfh in spleens was examined by flow cytometry. DBA/1 mice were divided into four groups: control, CIA-only, CIA+low-does IL-33(days 1-5), and CIA+high-does IL-33 (days 1-5 and 21-25). Arthritis severity was assessed using arthritis score, hematoxylin and eosin (H&E) staining, and Safranin O-Fast Green staining. Flow cytometry measured CXCR5/PD-1 expression on CD4+T cells and GL-7/FAS expression on B cells in draining lymph nodes (LN). ELISA was used to detect serum[AL1] IgG, IgM and anti-bovine collagen type II IgG2a and IgG2b antibodies concentrations. [AL1]LE: Please check if the section headings are assigned to appropriate levels.

In vitro experiments showed that IL-33 promoted Tfh differentiation and survival. IL-33 disrupted the Tfr/Tfh balance in the KLH model. In CIA, IL-33 exacerbated arthritis severity by enhancing Tfh cell proliferation in LNs and significantly altering GC B cell development and antibody production.

This study reveals a novel mechanism by which IL-33 exacerbates RA, suggesting its pro-inflammatory effects are mediated through Tfh cell polarization and GC activation. Key Points • The IL-33/ST2 axis promotes Tfh cell differentiation and viability. • IL-33 exacerbates arthropathy and enhances germinal center reactions in CIA mice. • IL-33 increases the Tfh cell ratio and ST2 expression on Tfh cells in CIA mice. • The IL-33/ST2 axis disrupts the Tfr/Tfh balance in KLH-immunized mice.