BACKGROUND AND OBJECTIVES: Bronchial instillation of lipopolysaccharide (LPS) provides a reversible model of lung inflammation that may resemble early stages of acute respiratory distress syndrome (ARDS). We investigated the distributions of T-cell subsets in the human airways and sought to determine whether pro- and anti-inflammatory T cells are involved in the local immune response to lung inflammation. METHODS: Bronchoalveolar lavage (BAL) was performed in 15 healthy volunteers, after which Escherichia coli LPS (4 ng/kg) was administered. BAL was repeated at 2, 4, 6, 8 or 24 h after instillation of LPS. RESULTS: BALF CD4+ and CD8+ T cells were characterized by expression of activation markers (HLA-DR+CD38+), the proportion of cells expressing naïve markers (CD45RA+CD27+CCR7+) was lower, and that of cells expressing effector memory markers (CD45RA-CD27+CCR7-) was higher, compared with peripheral blood. Bronchial LPS induced a local inflammatory response with recruitment of CD4+ (P=0.014), CD8+ T cells (P=0.034), an increase in the proportion of CD4+CD25+CD127lowFoxp3+ regulatory T cells (Tregs) (P=0.045) and a tendency towards an increase in CD4+CD161+ cells (P=0.071) were observed. CONCLUSIONS: A unique distribution of T cells with little day-to-day variation was found in human airways. An increase in Tregs after endobronchial LPS suggests a role for Tregs during early stages of pulmonary inflammation.