Extracellular DNA in bronchoalveolar lavage fluid as a candidate biomarker of disease severity in autoimmune pulmonary alveolar proteinosis

BACKGROUND: Autoimmune pulmonary alveolar proteinosis (aPAP) results from the neutralization of autoantibodies against granulocyte-macrophage colony-stimulating factor, which leads to alveolar macrophage (AM) dysfunction and surfactant accumulation. However, disease progression cannot be solely explained by surfactant overload. This study aimed to investigate whether defective efferocytosis in aPAP contributes to persistent apoptotic debris and accumulation of extracellular double-stranded DNA (dsDNA), which is a candidate biomarker of disease severity. METHODS: We analyzed bronchoalveolar lavage fluid (BALF) samples obtained from 13 patients with aPAP and 13 patients with other interstitial lung diseases (controls). Apoptotic debris was assessed cytologically, extracellular dsDNA was quantified fluorometrically with urea correction, and efferocytosis was evaluated using flow cytometry. Additionally, we analyzed correlations between BALF dsDNA levels and clinical indices. RESULTS: BALF samples from patients with aPAP contained abundant apoptotic debris and significantly higher dsDNA levels than those from controls. Further, AMs from patients with aPAP showed s markedly reduced uptake apoptotic cells, indicating altered efferocytosis-related processes. Corrected BALF dsDNA levels were negatively correlated with the arterial oxygen pressure to inspired oxygen fraction ratio and percent predicted diffusing capacity of the lung for carbon monoxide. CONCLUSIONS: Altered efferocytosis-related processes in patients with aPAP may promote the accumulation of apoptotic debris and extracellular DNA in the alveolar space. Further, dsDNA levels in BALF strongly reflect impaired gas exchange and provide a biomarker of disease severity. These findings further elucidate the pathogenesis of aPAP and establish extracellular DNA as a promising tool for disease monitoring and therapeutic evaluation.