Correlation of PD-1/PD-L1 Signaling Pathway with Treg/Th17 Imbalance from Asthmatic Children

<b><i>Background:</i></b> The balance between T helper 17 (Th17) and regulatory T cells (Treg) is a new paradigm in asthma pathogenesis, but no therapeutic targets could modulate the Th17/Treg balance specifically for asthma. Since previous studies have shown the programmed cell death-1(PD-1)/PD-ligand 1 (PD-L1) pathway is critical to immune homeostasis in this disease, we hypothesized that the PD-1/PD-L1 pathway might be involved in the regulation of Treg/Th17 imbalance in asthmatic children. <b><i>Methods:</i></b> The percentage of Treg and Th17 cells and the expression of PD-1 and PD-L1 were detected by flow cytometry in children with asthma and healthy controls. CD4⁺ T cells were stimulated with Th17 and Treg differentiating factors, and treated with anti-PD-1. Then cells were harvested and measured for Th17 and Treg percentages and Foxp3 and RORγt levels using RT-PCR. <b><i>Results:</i></b> We observed an inverse correlation between the percentages of Treg and Th17 cells, and the expression of PD-1 and PD-L1 in the two subsets also changed in the mild persistent and moderate to severe persistent groups compared with healthy controls. In vitro, administration of anti-PD-1 could decrease Th17 percentages and RORγt mRNA, and increase Treg percentages and Foxp3 mRNA in CD4⁺ T cells of children with asthma in the mild persistent and moderate to persistent groups. Additionally, the role played by anti-PD-1 in regulating Treg/Th17 balance was further confirmed in an asthmatic mouse model. <b><i>Conclusion:</i></b> Alteration of the PD-1/PD-L1 pathway can modulate Treg/Th17 balance in asthmatic children. Treatment with anti-PD-1 posed protective effects on asthma models, providing a novel theoretical target for asthma.