Expansion of profibrotic monocyte-derived alveolar macrophages in patients with persistent respiratory symptoms and radiographic abnormalities after COVID-19 [PASC]

As many as 10–30% of the nearly 750 million survivors of COVID-19 develop persistent symptoms that define the post-acute sequelae of COVID-19 (PASC) syndrome. To understand the molecular basis of this syndrome, we combined a machine learning based analysis of lung computed tomography (CT) with flow cytometry and single cell RNA-sequencing analysis of bronchoalveolar lavage fluid and nasal curettage samples in a cohort of thirty-five patients with respiratory symptoms and radiographic abnormalities more than 90 days after infection with COVID-19. CT images from patients with PASC revealed primarily fibrotic abnormalities involving 73 +/- 28% of the lung, most of which improved on subsequent imaging. The presence of profibrotic monocyte-derived alveolar macrophages in BAL fluid was significantly associated with increased levels of alveolar cytokines and fibrotic abnormalities on CT. Persistent infection with SARS-CoV-2 was identified in 6 patients and secondary bacterial or viral infections in two others. These findings suggest persistent alveolar inflammation characterized by the ongoing recruitment of monocyte derived alveolar macrophages is associated with fibrotic CT changes in some COVID-19 survivors with implications for diagnosis and therapy.