IL-35 modulates Tfh2 and Tfr cell balance to alleviate allergic rhinitis

Allergic rhinitis (AR) represents a persistent inflammatory condition affecting the upper respiratory tract, characterized by abnormal initiation of the immunoglobulin E (IgE)-mediated cascade. Follicular helper T (Tfh) cells and regulatory T (Tfr) cells are pivotal in orchestrating the development of IgE production in AR patients. IL-35, an anti-inflammatory cytokine, secreted by various cellular subpopulations. To investigate the interplay and underlying mechanisms between interleukin-35 (IL-35) and Tfr/Tfh2 cells in the context of AR. Experimental animal models employing BALB/c mice and IL-35-deficient mice underwent sensitization and challenge procedures utilizing ovalbumin (OVA) as the antigen in vivo. IL-35 was administered intranasally prior to OVA challenges. Nasal histopathological examination, PBMC isolation, Tfr/Tfh2 cell staining, Tfr/Tfh2 sorting and culture, and qPCR analysis as well as enzyme-linked immunosorbent assay (ELISA) were conducted for exploring the effect of IL-35 on Tfr/Tfh2 cells. Administration of IL-35 suppressed OVA-elicited allergic inflammation in murine models. IL-35 treatment led to an elevation in the proportion of peripheral blood Tfr cells and a decrease in Tfh2 cells. IL-35 also downregulated IL-4 and IL-21 protein expression by Tfh2 cells and upregulated IL-10 and transforming growth factor-β (TGF-β) production by Tfr cells. The anti-ICOS treatment abrogated the effect of IL-35 on Tfh2 and Tfr cells. Our study provided novel insights into the mechanisms of IL-35 action and its promoting effects on Tfh2 and inhibiting effects on Tfr cells by targeting key transcription factors, contributing to the understanding of the pathogenesis and treatment of AR.