IL-27-Dependent Lag3 Regulates CD4⁺ Foxp3⁺ Regulatory T Cells to Alleviate Airway Inflammation in Allergic Asthma

Allergic asthma is associated with a reduction in the number of regulatory T cells (Tregs). Although interleukin-27 (IL-27) has been shown to modulate Tregs potentially through the Lymphocyte-activation gene 3 (Lag3) pathway, the underlying mechanism remains incompletely defined. Objective: This study sought to determine whether IL-27 ameliorates airway inflammation in asthma by modulating Tregs in a Lag3-dependent manner. Acute asthma was induced in wild-type (WT) and Lag3 knockout (Lag3^-/-) mice through sensitization and challenge with house dust mite (HDM). A treatment group received intranasal recombinant IL-27 prior to challenges. In WT mice, IL-27 administration significantly attenuated airway inflammation, goblet cell hyperplasia, and total cell counts in bronchoalveolar lavage fluid (BALF), along with reduced levels of Th2 cytokines (IL-4, IL-5). It also upregulated T-bet (Th1) mRNA expression, downregulated GATA-3 (Th2) and RORγt (Th17) levels, and increased the proportions of CD4⁺ Foxp3⁺ Tregs, CTLA4⁺ Tregs, and Lag3⁺ Tregs in lung tissue. Conversely, in Lag3^-/- mice, the protective effects of IL-27 were completely abrogated, with no observed increases in Treg populations or suppression of Th2/Th17 immune responses. The anti-asthmatic effect of exogenous IL-27 is associated with increased Treg frequency and upregulation of inhibitory markers, with Lag3 serving as a pivotal target on Tregs.