Highlights
•  Severe COVID-19 patients display immune dysregulation or macrophage activation syndrome
•  Severe respiratory failure is associated with a major decrease of HLA-DR on CD14 monocytes
•  CD4 cell and NK cell cytopenias are characteristics of severe COVID-19
•  IL-6 blocker Tocilizumab partially rescues SARS-CoV-2-associated immune dysregulation