HUVEC supernatants, when stimulated with serum from patients with severe COVID-19 compared to control medium, showed a marked increase in a range of cytokines including IL-1α, IL-1Ra, IL-5, IL-6, IL-10, IL-12(p40), IL-18, IL-27, TNF-α, TGF-α, FGF-2, G-CSF, M-CSF, FLT-3L, fractalkine, MIG, eotaxin, IP-10, MIP-1β, MDC, and GROa (Figures 5, 6). This evidence concerns the gene FLT3LG and COVID-19.