Role of IL-35 in sublingual allergen immunotherapy

Background: Grass pollen-specific immunotherapy involves immunomodulation of allergen-specific T_H2 responses and induction of IL-10⁺ and/or TGF-β⁺CD4⁺CD25⁺ regulatory T cells (induced Treg cells). IL-35⁺CD4⁺CD25⁺ forkhead box protein 3-negative T (IL-35-inducible regulatory T [iT_R35]) cells have been reported as a novel subset of induced Treg cells with modulatory characteristics.

Objective: We sought to investigate mechanisms underlying the induction and maintenance of immunologic tolerance induced by IL-35 and iT_R35 cells.

Methods: The biological effects of IL-35 were assessed on group 2 innate lymphoid cells (ILC2s); dendritic cells primed with thymic stromal lymphopoietin, IL-25, and IL-33; and B and T_H2 cells by using flow cytometry and quantitative RT-PCR. Grass pollen-driven T_H2 cell proliferation and cytokine production were measured by using tritiated thymidine and Luminex MagPix, respectively. iT_R35 cells were quantified in patients with grass pollen allergy (seasonal allergic rhinitis [SAR] group, n = 16), sublingual immunotherapy (SLIT)-treated patients (SLIT group, n = 16), and nonatopic control subjects (NACs; NAC group, n = 16).

Results: The SAR group had increased proportions of ILC2s (P = .002) and IL-5⁺ cells (P = .042), IL-13⁺ cells (P = .042), and IL-5⁺IL-13⁺ ILC2s (P = .003) compared with NACs. IL-35 inhibited IL-5 and IL-13 production by ILC2s in the presence of IL-25 or IL-33 (P = .031) and allergen-driven T_H2 cytokines by effector T cells. IL-35 inhibited CD40 ligand-, IL-4-, and IL-21-mediated IgE production by B cells (P = .015), allergen-driven T-cell proliferation (P = .001), and T_H2 cytokine production mediated by primed dendritic cells. iT_R35 cells suppressed T_H2 cell proliferation and cytokine production. In addition, allergen-driven IL-35 levels and iT_R35 cell counts were increased in patients receiving SLIT (all, P < .001) and NACs (all, P < .001) compared with patients with SAR.

Conclusion: IL-35 and iT_R35 cells are potential novel immune regulators induced by SLIT. The clinical relevance of SLIT can be underscored by restoration of protective iT_R35 cells.