Saris A, Reijnders TDY, Nossent EJ, et al. - Via this observational study in patients with COVID-19 admitted to the intensive care unit (ICU), the pulmonary immune response during severe COVID-19 was investigated and compared with blood responses. Researchers obtained paired blood and BALF samples from 17 patients, four of whom died in the ICU. The most abundant cells in BALF were macrophages and T cells, with a high percentage of T cells expressing the ƴδ T cell receptor. Both CD4 and CD8 T cells in the lungs were mainly effector memory cells (87·3% and 83·8%, respectively); the exhaustion marker programmed death-1 was expressed at higher levels by these cells relative to the peripheral blood. They observed prolonged ICU stay (> 14 days) with a decreased proportion of activated T cells in peripheral blood and even more so in BALF. In fatal COVID-19 cases, they noted higher T cell activation in blood, but not in BALF. BALF had more pronounced increased levels of inflammatory mediators than plasma. Overall findings revealed a unique local profile of the bronchoalveolar immune response in COVID-19 that strongly differs from the immune profile in peripheral blood.