FLT3LG and COVID-19: Patients with moderate to severe COVID-19 significantly increased the production of mucosal pro-inflammatory factors, including IL-8, TNF-β, IL-2, IL-9, IL-17A, Flt-3L, GM-CSF, IL-12p40, MDC, VEGF, IL-15, sCD40L, and TGF-α, during the early response phase (Fig. 3C through O).