Sublingual allergen immunotherapy (SLIT), a disease-modifying treatment for allergic rhinitis, can produce long-term therapeutic improvements through immunological responses such as the production of regulatory B (Breg) and T (Treg) cells. IL-35, the newest member of the IL-12 class, is an anti-inflammatory cytokine generated by Breg and Treg cells. There has been little research on the role of IL-35 in allergic rhinitis and during SLIT. This study covers current studies related to IL-35 and its function in SLIT. Recombinant IL-35 protein can stimulate the production of immunosuppressive IL-35-producing Breg and Treg cells. In allergic rhinitis patients, levels of IL-35 and IL-35-inducible Treg (iTR35) cells are dysregulated, which can be restored by SLIT. T cell proliferation, Th2 cytokine production, and B cell synthesis of IgE antibodies are all suppressed by IL-35-mediated tolerance to allergens.

Emerging research suggests that IL-35 and iTR35 cells may play a role in tolerance maintenance during SLIT. A deeper knowledge of the involvement of IL-35 and iTR35 cells may open up new pathways for the creation of clinical biomarkers to measure the success of allergen immunotherapy as well as innovative treatment options for allergic rhinitis.