After 24 h of viral infection, overexpression of SERPINE1/PAI-1 blocked trypsin-mediated cleavage of HA0 into HA1 and HA2 (Figure 7(J)), suggesting that SERPINE1/PAI-1 regulates HA maturation and reduces viral infectivity, thereby inhibiting viral replication. This evidence concerns the gene SERPINE1 and viral infectious disease.