Inducible CD4 ⁺LAP ⁺Foxp3 ^- regulatory T cells suppress allergic inflammation

Regulatory T cells (Tregs) play a critical role in the maintenance of airway tolerance. We report that inhaled soluble Ag induces adaptive Foxp3 ⁺ Tregs, as well as a regulatory population of CD4 ⁺ T cells in the lungs and lung-draining lymph nodes that express latency-associated peptide (LAP) on their cell surface but do not express Foxp3. Blocking the cytokine IL-10 or TGF-β prevented the generation of LAP ⁺ Tregs and Foxp3 ⁺ Tregs in vivo, and the LAP ⁺ Tregs could also be generated concomitantly with Foxp3 ⁺Tregs in vitro by culturing naive CD4 ⁺ T cells with Ag and exogenous TGF-β. The LAP ⁺ Tregs strongly suppressed naive CD4 ⁺T cell proliferation, and transfer of sorted OVA-specific LAP ⁺ Tregs in vivo inhibited allergic eosinophilia and Th2 cytokine expression in the lung, either when present at the time of Th2 sensitization or when injected after Th2 cells were formed. Furthermore, inflammatory innate stimuli from house dust mite extract, nucleotide-binding oligomerization domain containing 2 ligand, and LPS, which are sufficient for blocking airway tolerance, strongly decreased the induction of LAP ⁺ Tregs. Taken together, we concluded that inducible Ag-specific LAP ⁺ Tregs can suppress asthmatic lung inflammation and constitute a mediator of airway tolerance together with Foxp3 ⁺ Tregs.