Fibroblasts (1610 4 ) in a volume of 100 ml were seeded in 96well plates. HB15-UL84prluc (275 pfu) was preincubated with serial log 2 dilutions of complement inactivated serum or mab in a volume of 50 ml in culture medium for 1 h at 37uC. The mixture was added to fibroblasts for 4 h. The inoculum was removed and the cells were incubated at 37uC for 48 h. Cells were lysed using 100 ml Glo Lysis Buffer (Promega, USA) per well. 30 ml of each cell lysate was placed in white 96-well LIA-plates. Per well, 50 ml assay buffer (15 mM KH 2 PO 4 , 25 mM glycylglycine, 1 M MgSO 4 , 0.5 M EGTA, 5 mM ATP, 1 mM DTT) was added. Luciferase activity was measured by injection of 50 ml D-luciferin (P.J.K., Germany) solution per well (in 25 mM glycylglycine, 1 M MgSO 4 , 0.5 M EGTA, 2 mM DTT and 0.05 mM D-luciferin) and detection of chemiluminescence was performed by an Orion Microplate Luminometer (Berthold Technologies, Germany). Neutralization assays using endothelial and epithelial cells were performed using the HCMV isolate TB40E as described [69] . The influence of complement on neutralization capacity of monoclonal antibodies was tested by inclusion of 5% rabbit complement (Cedarlane Labs, Canada) in the neutralization assay.