Monocytes from patients with severe COVID-19 are hyperresponsive to P-selectin and fibrinogen regarding inflammatory cytokine secretion. Monocytes (1 × 105) from patients with severe COVID-19 or control participants were plated on recombinant human albumin, P-selectin, or fibrinogen coated surfaces. (A) The number of monocytes (DAPI, nuclei) adhered on each condition is shown. Scale bar represents 100 µm. (B-D) The concentration of MCP-1/CCL2 (B), TNF-α (C), and IL-1β in each condition (D). Bars represent mean ± standard error of the mean of monocytes from 5 independent control participants and 6 independent patients with severe COVID-19. #P < .05 compared with monocytes from control participants in the same condition; *P < .05 compared with albumin.