Dissecting the common and compartment-specific features of COVID-19 severity in the lung and periphery with single-cell resolution.

Severe COVID-19 is accompanied by rampant immune dysregulation in the lung and periphery, with immune cells of both compartments contributing to systemic distress. The extent to which immune cells of the lung and blood enter similar or distinct pathological states during severe disease remains unknown. Here, we leveraged 96 publicly available single-cell RNA sequencing datasets to elucidate common and compartment-specific features of severe to critical COVID-19 at the levels of transcript expression, biological pathways, and ligand-receptor signaling networks. Comparing severe patients to milder and healthy donors, we identified distinct differential gene expression signatures between compartments and a core set of co-directionally regulated surface markers. A majority of severity-enriched pathways were shared, whereas TNF and interferon responses were polarized. Severity-specific ligand-receptor networks appeared to be differentially active in both compartments. Overall, our results describe a nuanced response during severe COVID-19 where compartment plays a role in dictating the pathological state of immune cells.