Characterization of the Inflammatory Response to Severe COVID-19 Illness

Abstract

<b>Rationale:</b> Coronavirus disease (COVID-19) is a global threat to health. Its inflammatory characteristics are incompletely understood.<b>Objectives:</b> To define the cytokine profile of COVID-19 and to identify evidence of immunometabolic alterations in those with severe illness.<b>Methods:</b> Levels of IL-1β, IL-6, IL-8, IL-10, and sTNFR1 (soluble tumor necrosis factor receptor 1) were assessed in plasma from healthy volunteers, hospitalized but stable patients with COVID-19 (COVID_stable patients), patients with COVID-19 requiring ICU admission (COVID_ICU patients), and patients with severe community-acquired pneumonia requiring ICU support (CAP_ICU patients). Immunometabolic markers were measured in circulating neutrophils from patients with severe COVID-19. The acute phase response of AAT (alpha-1 antitrypsin) to COVID-19 was also evaluated.<b>Measurements and Main Results:</b> IL-1β, IL-6, IL-8, and sTNFR1 were all increased in patients with COVID-19. COVID_ICU patients could be clearly differentiated from COVID_stable patients, and demonstrated higher levels of IL-1β, IL-6, and sTNFR1 but lower IL-10 than CAP_ICU patients. COVID-19 neutrophils displayed altered immunometabolism, with increased cytosolic PKM2 (pyruvate kinase M2), phosphorylated PKM2, HIF-1α (hypoxia-inducible factor-1α), and lactate. The production and sialylation of AAT increased in COVID-19, but this antiinflammatory response was overwhelmed in severe illness, with the IL-6:AAT ratio markedly higher in patients requiring ICU admission (<i>P</i> < 0.0001). In critically unwell patients with COVID-19, increases in IL-6:AAT predicted prolonged ICU stay and mortality, whereas improvement in IL-6:AAT was associated with clinical resolution (<i>P</i> < 0.0001).<b>Conclusions:</b> The COVID-19 cytokinemia is distinct from that of other types of pneumonia, leading to organ failure and ICU need. Neutrophils undergo immunometabolic reprogramming in severe COVID-19 illness. Cytokine ratios may predict outcomes in this population.