Down-regulation of HLA-DR at 1 day after infection on HCMV-infected cells. The expression of HLA-DR was analyzed at 3 to 24 hours after infection using flow cytometry. The expression of HLA-DR on mock-infected cells (gray line) and HCMV-infected cells (black line) at 3, 12, and 24 hours after infection is shown in panels A, B, and C, respectively.