Blood fibrocytes are associated with severity and prognosis in COVID-19 pneumonia

Ghanem, Mada; Homps-Legrand, Méline; Garnier, Marc; Morer, Lise; Goletto, Tiphaine; Frija-Masson, Justine; Wicky, Paul-Henri; Jaquet, Pierre; Bancal, Catherine; Hurtado-Nedelec, Margarita; de Chaisemartin, Luc; Jaillet, Madeleine; Mailleux, Arnaud A; Quesnel, Christophe; Poté, Nicolas; Debray, Marie-Pierre; de Montmollin, Etienne; Neukirch, Catherine; Borie, Raphael; Taillé, Camille; Crestani, Bruno

Increased blood fibrocytes are associated with a poor prognosis in fibrotic lung diseases. We aimed to determine whether the percentage of circulating fibrocytes could be predictive of severity and prognosis during Coronavirus disease 2019 (COVID-19) pneumonia. Blood fibrocytes were quantified by flow cytometry as CD45+/CD15-/CD34+/Collagen-1+cells in patients hospitalized for COVID-19 pneumonia. In a subgroup of patients admitted in ICU, fibrocytes were quantified in blood and broncho-alveolar lavage (BAL). Serum amyloid P (SAP), TGF-b1,CXCL12, CCL2, and FGF2 serum concentration were measured in serum. We included 57 patients in the Hospitalized group (median age 59 years [23-87]) and 16 Healthy controls. The median percentage of circulating fibrocytes was higher in patients compared to controls (3.6% [0.2-9.2] vs. 2.1% [0.9-5.1], p=0.04). Blood fibrocyte count was lower in the 6 patients who died compared to survivors (1.6% [0.2-4.4] vs. 3.7% [0.6-9.2], p=0.02). Initial fibrocyte count was higher in patients showing a complete lung CT resolution at 3 months. Circulating fibrocyte count was decreased in the ICU group (0.8% [0.1-2.0]) whereas BAL fibrocyte count was 6.7% [2.2-15.4]. Serum SAP and TGF-b1 concentrations were increased in Hospitalized patients. SAP was also increased in ICU patients. CXCL12 and CCL2 were increased in ICU patients, and negatively correlated with circulating fibrocyte count. We conclude that circulating fibrocytes were increased in patients hospitalized for COVID-19 pneumonia and a lower fibrocyte count was associated with an increased risk of death and a slower resolution of lung CT opacities.