Immunofluorescence of p52 antigen in P3HR-1 cells superinfected with CMV. Immunofluorescence staining was performed to give a qualitative analysis of CMV protein expression and to further show susceptibility of infection. Approximately 50,000 P3HR-1 cells for each experimental group were subjected to a cytospin for antigen staining. The cells were fixed in acetone and methanol (1:1) mixture and stained with the appropriate dilution of the FITC labelled antibody. Presence of the p52 antigen was positive at all time points (24, 48, 72, 96, 120, and 168 hours), slide shown is at 24 hours post CMV superinfection. Uninfected cells and cells incubated with UV-irradiated CMV showed no presence of the p52 antigen (data not shown). Positive control slides were stained with the antibody to show that the antibody was working (data not shown).