Cell Host Microbe https://bit.ly/35X1jay (2020)

A subset of patients with COVID-19 that require hospitalization undergo a rapid deterioration accompanied by respiratory failure. In Cell Host & Microbe, Koutsoukou and colleagues compare the clinical parameters of patients with COVID-19 and patients hospitalized for bacterial sepsis and, retrospectively, patients infected by the 2009 H1N1 influenza virus. Patients with COVID-19 with severe respiratory failure have distinct immune profiles that contrast with the profiles of patients with bacterial sepsis. In particular, although the patients with COVID-19 have higher numbers of circulating monocytes, they have low numbers of natural killer cells and lymphocytes (including CD4+ and CD8+ T cells and CD19+ B cells). Monocytes from patients with severe COVID-19 disease have sustained expression of the cytokines tumor necrosis factor (TNF) and interleukin-6 (IL-6), suggesting a dysregulation of cytokine production. Additionally, the expression of HLA-DR on monocytes from patients with COVID-19 is decreased relative to that of healthy volunteers; this effect is inversely correlated with IL-6 serum concentrations. The expression of HLA-DR on healthy monocytes decreases following culture with plasma from patients with COVID-19 who have immune dysregulation, an effect that could be partially reversed by the addition of tocilizumab to block IL-6 signaling. Indeed, for a subset of patients with severe COVID-19, tocilizumab treatment increased lymphocyte counts, indicating that some patients may be able to rebound from viral-induced immune paralysis.