Platelet monocyte interaction associate with monocyte inflammatory activation in COVID-19. (A) The percentage of platelet-monocyte complexes among classical, intermediate, and nonclassical monocyte subsets from SARS-CoV-2-negative control participants and patients with mild to severe COVID-19 syndrome. (B) The percentage of platelet-monocyte complexes in HLA-DR-positive or negative monocytes from patients with severe COVID-19. (C) The Log2 fold change of the transcripts for P-selectin and fibrinogen receptors P-selectin glycoprotein ligand 1 (SELPG), integrin β₁ (ITGB1), integrin β₂ (ITGB2), integrin α_X (ITGAX), and integrin α_M (ITGAM) in monocytes from patients with severe COVID-19. *P < 2.5 × 10⁻¹³. (D-F) The percentage of CD11b-positive monocytes in blood from SARS-CoV-2-negative control participants and patients with mild to severe COVID-19 syndrome (D); or from patients with severe COVID-19 stratified according to the requirement of invasive mechanical ventilation or noninvasive O₂ supplementation (E) or the 28-day mortality outcome as survivors or nonsurvivors (F). The horizontal lines in the box plots represent the median, the box edges represent the interquartile ranges, and the whiskers indicate the minimal and maximal value in each group. *P < .05 compared with control in the same monocyte subset; #P < .05 between selected groups.