Fig. 3.

Growth of SARS-CoV-2 on DF1 and MDCK cells expressing either human ACE2, human TMPRSS2, or both (++). (A) DF1, DF1 expressing human ACE2, DF1 expressing human TMPRSS2, DF1 expressing both human ACE2 and TMPRSS2 (++), MDCK, MDCK expressing human ACE2, MDCK expressing human TMPRSS2, MDCK expressing both human ACE2 and TMPRSS2 (++), and Vero cells were inoculated with SARS-CoV-2 at multiplicity of infection (MOI) of 1. At time points indicated, supernatant samples were taken for RNA extraction and determination of viral titers by RT-PCR. The values shown are mean±standard deviation of triplicate samples. Two-way analysis of variance with Tukeys multiple comparison test was performed on titers at 48 h post inoculation to determine the statistical difference in virus titer between the cell lines. Lines with different lowercase letters indicate differences (p < 0.05). (B) Pass 2 of virus from cell culture lines expressing human ACE2, TMPRSS2, or both. After 72 h of growth, supernatants of pass 1 were transferred onto fresh monolayers of cells, allowed to absorb for 1 h and removed. Fresh media was added and samples were taken at time points indicated to determine virus titer by RT-PCR. Statistical analysis was performed at 48 h post inoculation. ND=Not detected.