ACE2 and viral infectious disease: For instance, Hamming and colleagues reported high levels of ACE2 expression in A549 cells [58], but others observed low levels of it [70, 89] and found that exogenous overexpression of ACE2 was required to render A549 cells permissive to viral infection and suggested that this difference could be due to different lineages of cell lines that may have evolved during the in vitro cell culture.