Increased lung monocyte infiltration in Fibrotic Interstitial Lung Diseases.

<bold>Background:</bold> Monocytes migrate to the lung upon injury, however, their role in idiopathic pulmonary fibrosis(IPF) pathogenesis is not yet understood. Current data suggest that high blood monocyte count in IPF patients is associated with worse prognosis. We evaluated monocyte infiltration in bronchoalveolar lavage(BAL) from patients with fibrotic Interstitial Lung Diseases (ILDs). <bold>Methods:</bold> This was a single-center study performed at the University Hospital of Crete. 201 patients with IPF and 144 with non-IPF fibrotic ILDs (chronic hypersensitivity pneumonitis, ILD associated with systemic autoimmune rheumatic diseases, and other idiopathic interstitial pneumonias, including idiopathic pneumonia with autoimmune features and unclassifiable ILD),were included. Bronchoscopy was performed at the time of diagnosis, and BAL was obtained.22 individuals, who underwent bronchoscopy for the investigation of haemoptysis, without any detectable lung abnormalities, were also included as a control group. <bold>Results:</bold> The percentage of BAL monocytes was higher in patients with IPF and non-IPF ILDs, compared to controls. No differences were observed among fibrotic ILDs. Further analysis of BAL cellular composition showed increased percentages of eosinophils, neutrophils, and higher neutrophil to lymphocyte ratio(NLR) in fibrotic ILDs. Interestingly, in non-IPF patients, lung monocyte infiltration correlated with eosinophil and neutrophil percentages, as well as NLR. However, BAL monocytes were not associated with progression or survival in fibrotic ILDs, in contrast to blood monocyte counts, which were associated with higher mortality. <bold>Conclusion:</bold> Our results showed increased lung monocyte infiltration in patients with fibrotic ILD.