FIG. 1.

Monocytes can be infected by endotheliotropic strains of HCMV, but the infection is blocked at early stages of the viral cycle. (A) At 24 h after infection, the IE (IE1-2), early (p52), and early-late (phosphoprotein pp65 and glycoprotein gB) viral antigens were detected by immunofluorescence (green staining) in monocytes inoculated with TB40E, AD169, and UV-inactivated TB40E (UV-TB40E) at an MOI of 5. Mock-infected monocytes were the negative controls. All photographs are from 1 donor representative of 20 (original magnification, ×60). Insets show in detail the pattern of fluorescence for a single cell (original magnification, ×100). (B) The percentages of IE1-2, p52, gB, and pp65 antigen-positive cells were evaluated at different time points after TB40E infection as the ratio of the number of positive cells to the total number of cells. Values are the mean ± SD of 10 different microscopic fields. The kinetic analysis from one donor representative of 20 is shown. (C) At different time points after infection, the amount of infectious virus present in monocyte supernatants and cytoplasmic extracts was evaluated by titration. Monocytes (3 × 10⁶) were inoculated at time t = 0 with 1.5 × 10⁷ PFU of TB40E (corresponding to an MOI of 5), and at 12 h postinfection they were washed with acid buffer in order to remove the unabsorbed viral particles. The number of viable monocytes (line graph) was evaluated at each time point. Uninfected and TB40E-infected monocytes were similar in viability and morphology.