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

Abstract

Introduction: COVID-19 can lead to severe acute pneumonia in 15-20% of patients. The increase of circulating fibrocytes is associated with a poor prognosis in fibrotic lung diseases and acute respiratory distress syndrome. We aimed to quantify the % of circulating fibrocytes in patients hospitalized for COVID-19, in order to determine their prognosis value.

Methods: Blood fibrocytes were quantified by flow cytometry as CD45+/CD15-/CD34+/Collagen-1+. Clinical and imaging data were obtained at inclusion and at 3 months. In a group of ICU patients, we quantified fibrocytes in blood and broncho-alveolar lavage fluid (BALF).

Results: We included 57 patients admitted for COVID-19 pneumonia (median age 59 years [23-87]) and 16 healthy controls. Samples were taken 11 days [4-31] after first symptom. The median % of circulating fibrocytes was higher in patients compared to controls (3.6% vs 2.1%, p=0.04). The % was lower in patients who died (6/57) as compared to survivors (1.6% versus 3.7%, p=0.02). Fibrocyte % did not correlate with biological severity markers. At 3-months follow-up, a complete resolution of CT opacities was observed in 13/32 patients and was associated with a significantly higher initial fibrocyte count as compared to patients with an incomplete resolution (4.5% vs 3.4%, p=0.04). In 7 ICU patients (median age 62 years [50-73]), blood fibrocyte count was 0.94% while BALF fibrocyte count was 6.7%.

Conclusion: Circulating fibrocytes were increased in patients with COVID-19 pneumonia. Lower fibrocyte count was associated with an increased risk of death and a slower resolution of lung CT opacities, possibly resulting from an alveolar recruitment of fibrocytes in severe cases.