Virus infection of human monocytes induces differentiation into DCs. (A) Human PBMCs were infected for 6 hours with the indicated virus at a multiplicity of infection (MOI) of 10, and surface expression of IAV hemagglutinin or virus-encoded enhanced green fluorescent protein on CD3⁺ T cells, CD14⁺ monocytes, CD19⁺ B cells, CD56⁺ NK cells, lineage-negative (CD3/14/19/56)⁻HLA-DR⁺CD11c⁺CD123⁻ cDCs, or lineage-negative HLA-DR⁺CD11c⁻CD123⁺ pDCs was determined by flow cytometry. The results represent 1 of 2 separate experiments with similar results. (B) Flow cytometric analysis of T/monocyte/B/NK cells 6 or 18 hours after IAV infection at indicated MOI. % Max indicates percent of maximum. (C) Effect of IAV infection at indicated MOI 6 or 18 hours after infection on lineage-negative HLA-DR⁺ DC population (red box; left panel) or on cDC (circled CD123^lowCD11c⁺ population)/pDC (circled CD123⁺CD11c⁻ population) populations (middle panel), and the cell number of monocytes, cDCs, and pDCs in 5 × 10⁵ PBMCs 18 hours after IAV infection (right panel). (D) CD14⁺ monocyte-depleted PBMCs were infected for 18 hours with IAV and then stained with lineage markers and HLA-DR. The results in panels B through D are representative examples of 5 independent experiments. (E) Purified CD14⁺ monocytes were infected for 6 and 18 hours with IAV and then stained with anti-hemagglutinin antibody. The results are representative examples of 3 independent experiments.