COVID-19 acute respiratory distress syndrome promotes a specific alternative macrophage polarization

Acute respiratory distress syndrome (ARDS) alveolar environment induced a pro-repair anti-inflammatory macrophage polarization. However, patients with coronavirus disease 2019 (COVID-19) ARDS frequently exhibit a huge lung inflammation and present pulmonary scars and fibrosis more frequently than patients with non-COVID-19 ARDS, suggesting that the COVID-19 ARDS alveolar environment may drive a more inflammatory or pro-fibrotic macrophage polarization. This study aimed to determine the effect of the COVID-19 ARDS alveolar environment on macrophage polarization. The main finding was that broncho-alveolar lavage fluids (BALF) from patients with early COVID-19 ARDS drove an alternative anti-inflammatory polarization in normal monocyte-derived macrophages; characterized by increased expressions of CD163 and CD16 mRNA (3.4 [2.7-7.2] and 4.7 [2.6-5.8] fold saline control, respectively - p = 0.02), and a secretory pattern close to that of macrophages stimulated with IL-10, with the specificity of an increased production of IL-6. This particular alternative pattern was specific to early ARDS (compared with late ARDS) and of COVID-19 ARDS (compared with moderate COVID-19). The early COVID-19 ARDS alveolar environment drives an alternative anti-inflammatory macrophage polarization with the specificity of inducing macrophage production of IL-6.