CCL4 and COVID-19: Single-cell transcriptomic analysis of PBMC in 7 hospitalized COVID-19 patients revealed a depletion of CD16+ monocytes in peripheral blood and the induction of an ISG signature in CD14+ monocytes, but detected no substantial induction of pro-inflammatory cytokine genes, such as TNF, IL6, IL1β, CCL3, CCL4 or CXCL2 in these cells, suggesting that peripheral monocytes are no major contributors to the cytokine response in COVID-19 (155).