While macrophages in COVID-19 samples expressed chemokines that primarily engage CC and CXC family chemokine receptors on neutrophils (Figure 4D, orange box), macrophages in influenza samples expressed ligands that engage formyl peptide receptors (FPR), FPR1 and FPR2 (Figure 4D, pink box). Here, CXCR1 is linked to influenza.