Peripheral immune checkpoint gene expression as diagnostic biomarkers in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a relatively rare and progressive fibrotic interstitial lung disease with limited annual incidence and poor prognosis. Increasing evidence suggests that immune dysregulation, including altered immune checkpoint and innate regulatory signaling pathways, may contribute to disease pathogenesis. This study aimed to investigate peripheral blood expression levels of PD-1, PD-L1, TIM-3, and TOLLIP genes and to evaluate their diagnostic potential in patients with IPF.

This case-control study included 20 IPF patients and 20 age-matched healthy controls. Gene expression levels were quantified using real-time quantitative polymerase chain reaction (RT-qPCR) and calculated using the ΔCt method. Diagnostic discrimination was assessed by receiver operating characteristic (ROC) analysis.

PD-L1 (p < 0.001) and TOLLIP (p = 0.002) ΔCt values were significantly higher, indicating reduced relative gene expression. ROC analysis demonstrated strong diagnostic performance for PD-L1 (AUC = 0.883) and TOLLIP (AUC = 0.865). The combined PD-L1 + TOLLIP biomarker panel demonstrated superior diagnostic accuracy (AUC = 0.948). Internal validation using bootstrap resampling confirmed model stability (mean AUC = 0.950; 95% CI: 0.85-1.00).

In conclusion, peripheral blood PD-L1 and TOLLIP expression levels are significantly downregulated in patients with idiopathic pulmonary fibrosis. The combined PD-L1 + TOLLIP biomarker panel demonstrated strong diagnostic discrimination (AUC = 0.948), supporting the potential clinical utility of peripheral immune regulatory gene signatures as minimally invasive biomarkers in IPF. Larger prospective studies are warranted to validate these findings and to explore their potential role in clinical decision-making.