PF4 and COVID-19: Potential candidates that have been proposed thus far include PF4, whose gene expression is increased ~5.5 fold in lung tissue of fatal COVID-19 cases (198), and an array of NET-inducing cytokines and chemokines such as IL-6, IL-8, TNF-α, IL-1β and CCL20 whose expression levels are up-regulated in COVID-19 BALF samples and/or human lung epithelial cells infected with SARS-CoV-2 (188, 189, 194, 195).