CXCL9 and COVID-19: This classifier reinforced the prognostic importance of monocyte/macrophage, NK cell, and Th1-pathway activation, with prediction of severe COVID-19 driven by higher concentrations of IL-7, CXCL10, IL-15, and CXCL9, and lower concentrations of MDC and IL-5 (Fig. 1d, e).