Immune responses to SARS-CoV-2 in the lung.

Human immunity to SARS-CoV-2 has been characterised extensively; however, our understanding of the immune responses in the lung, the site of infection, is limited. A previous study assessing bronchoalveolar lavage (BAL) samples showed a higher proportion of inflammatory monocytes and macrophages in patients with severe COVID-19 disease. In contrast, the moderate patients showed an accumulation of clonally expanded CD8 T cells.1 The data suggested an enhanced inflammation in the lungs, but paired analysis of peripheral blood and BAL is even more limited.2 In this issue, Saris et al present a study in which the authors characterised the cellular immune composition of paired blood and BAL samples from 17 patients with severe COVID-19 infection, of which 4 patients were deceased.3 They observed a significant increase in monocyte populations in BAL of all patients, consistent with the idea that activated blood monocytes migrate to the …