Acute lung injury (ALI) is a severe inflammatory disease, for which no specific treatment exists. The decreased ratio of regulatory T cells (CD4⁺ CD25⁺ FoxP3 Tregs) and Th17 cells is implicated in ALI and inflammation. We here investigated whether maintaining the balance of CD4⁺ CD25⁺ Foxp3⁺ Tregs and Th17 cells can alleviate lung injury. For CD4⁺ CD25⁺ FoxP3 Treg depletion, 200 μg of an anti-CD25 antibody was administered intraperitoneally per mouse on days -3 and -1 before lipopolysaccharide (LPS) instillation. And 150 μg of TGF-β was administered intraperitoneally per mouse on day 0 after LPS instillation. To down-regulate of Th17 cells, 200 μg per mouse of isotype, IL-17 or IL-22 antibodies were injected intraperitoneally into mice at days 0 after LPS instillation. We detected lung morphology; lung wet-to-dry weight ratio; protein concentration, the count of total cells, neutrophils and macrophages, and cytokines in bronchoalveolar lavage fluid (BALF). And we also evaluated the percentage of CD4⁺ CD25⁺ Foxp3⁺ Tregs in lung, and Th17 cells in lung. CD4⁺ CD25⁺ Foxp3⁺ Tregs depletion via anti-CD25 treatment or TGF-β neutralization delayed recovery of ALI. The prolonged inflammation was mainly dominated by neutrophils, macrophages and Th17 cells. Furthermore, inhibition of Th17 cells via monoclonal antibodies against IL-17 and IL-22 alleviated ALI inflammation by inhibiting the recruitment of neutrophils and macrophages, increasing the number of CD4⁺ CD25⁺ Foxp3⁺ Tregs. Our findings support a critical role for CD4⁺ CD25⁺ Foxp3⁺ Tregs in regulating from ALI pathophysiology, and a potential therapeutic role for the inhibition of Th17 cells in ALI treatment. These findings provide a rationale for treating patients with ALI by modulating CD4⁺ CD25⁺ Foxp3⁺ Tregs and Th17 cells.

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