Fibroblasts were seeded at 3610 4 cells per well in 96-well plates. HB15-UL84prluc was preincubated with individual mabs for 1 h at 37uC at concentrations ensuring complete neutralization. Cells and the virus/mab mixture were cooled to 4uC and the virus/mab mixture was added to the cells at a multiplicity of infection (m.o.i.) of 0.5. Following incubation for 1h at 4uC, cells were washed three times with ice-cold PBS and cell lysates were prepared by freezing/thawing. DNA was extracted from the lysates using a MagNA Pure LC (Roche, Germany) instrument and quantitative real-time PCR was performed on an ABI PRISM 7500. To control for recovery of cells, copy numbers of albumine DNA was determined in parallel to HCMV and HCMV copies were calculated per 1000 copies albumine. Primers : CMV 59:GAG-CAGACTCTCAGAGGATCGG; CMV 59: AAGCGGCCTCT-GATAACCAAG; Albumine 59: GTGAACAGGCGACCATG-CT; Albumine 39: GCATGGAAGGTGAATGTTTCAG. For the penetration assay, precooled cells were preincubated with virus at a m.o.i. of 0.2 for 1 h at 4uC, washed twice with ice-cold PBS and incubated for 2 h at 37uC with log 10 dilutions of mabs. After incubation, remaining mabs were removed by washing twice with PBS before cells were incubated for 48 h at 37uC. Subsequent steps were carried out according to the virus neutralization assay. Chemiluminescence of virus only was set to 100%.