FIG 2.

Susceptibility of human primary immune cells to SARS-CoV-2 infection. (A) Human monocyte-derived DCs and MΦs from four different blood donors were separately infected with SARS-CoV-2 Fin-1 and Fin-25 strains at an MOI of 1 TCID₅₀/cell, and samples were collected at different times after infection as indicated in the figure. From total cellular RNA samples, viral RNA expression was analyzed using a SARS E gene-specific qRT-PCR assay. Individual donors are shown with different symbols, and the results are shown as relative copy numbers over the mock sample. Data are presented as the means ± SEM of cells generated from four independent blood donors. SARS-CoV-2-infected cells from the same four donors were collected and pooled for viral protein expression analysis and immunoblotted using anti-N (SARS-CoV) and anti-GAPDH antibodies. Fin-1-infected Vero E6 cell extract was used as a positive control (Pos Ctrl). From the same cell cultures, the supernatant samples were harvested for virus titrations in Vero E6 cells, and titers are shown as log TCID₅₀/ml representing the means ± SEM from DC or MΦ cultures from four different blood donors. (B) Human monocytes and lymphocytes from four different donors were infected with SARS-CoV-2 Fin-1 and SARS-CoV (MOI of 1) for 6, 24, and 48 h, and cellular RNA samples from different donors were pooled and analyzed for the expression of viral RNA. The data are shown as a relative copy number over the mock sample. (C) Human PBMCs from four different blood donors were separately infected with the SARS-CoV-2 Fin-25 strain and IAV at an MOI of 1, and samples were collected at different times after infection as indicated in the figure. SARS-CoV-2- or IAV-infected cells were harvested, fixed separately, and double stained with indicated antibodies for specific cell surface markers and viral antigens. The samples were analyzed with a FACSCanto II (BD) device using FACSDiva software. Data are presented as the means ± SEM of cells generated from four independent blood donors. Representative histogram patterns from flow cytometric analysis of SARS-CoV-2 Fin-25 and IAV virus-infected CD14-positive cells from one donor is shown. A 6-h time point was included to the IAV-infected samples due to the faster infection kinetics.