PF4 and COVID-19: Different serum proteins that have been reported as altered after COVID-19 infection (i.e. CRP, von Willebrand factor, HSPA5, or LMAN2) in several proteomic studies (Table S9) were directly connected with the protein changes seen in ECFCs in the current approach in response to COVID-19 positive sera (SURF4, LAMP2, PF4, CTSL or CTSD, among others) (Figure 7).