Modulating dendritic cell function in allergic asthma with Toxoplasma gondii serine protease inhibitor 1.

Tolerogenic adjuvants can enhance allergy vaccine efficacy. We previously showed that intranasal administration of recombinant Toxoplasma gondii serine protease inhibitor 1 (rTgPI-1) with ovalbumin alleviates asthma symptoms in mice. This study investigates the immunomodulatory mechanisms of rTgPI-1, focusing on its effect on dendritic cells (DCs). Bone marrow-derived DCs (BMDCs) were generated in the presence of rTgPI-1 and analyzed for their phenotype. rTgPI-1 exposed BMDCs showed reduced CD80, CD86, and MHCII, increased PDL-1 and CD45Rb, and a higher IL-10/IL-12 ratio. These BMDCs induced fewer CD69⁺CD4⁺ T cells, decreased proliferation and secretion of IL-17 and IL-4, and increased CD4⁺FoxP3⁺ T cells. In vivo, intranasal co-administration of rTgPI-1 with allergen in asthmatic mice reduced CD80high/CD86high DCs, expanded lung CD4⁺FoxP3⁺ regulatory T cells, and decreased the cDC2 subset, correlating with reduced IL-4 levels. Importantly, nafamostat mesylate-a synthetic serine protease inhibitor previously shown to alleviate asthma symptoms-failed to induce FoxP3⁺ T cells both in vitro and in vivo, underscoring the unique tolerogenic activity of rTgPI-1. Finally, stimulation of peripheral blood mononuclear cells from mite-allergic patients with house dust mite extract in the presence of rTgPI-1 led to reduced allergen-specific IL-4 and IL-5 secretion. These findings demonstrate that rTgPI-1 promotes a semimature, tolerogenic DC phenotype, suppresses T cell activation, and fosters regulatory T cell differentiation. Moreover, rTgPI-1 selectively modulates DC subsets in vivo. The observed effects on patient-derived PBMCs support its potential for further preclinical development as an adjuvant for allergen-specific immunotherapy.