FIG. 4.

Neutralization activity of MAb 1418-1 (VP1u) and MAb 860-55D (Caps). (A) B19 was preincubated with the MAbs or PBS (no antibody [No Ab]) for 1 h at 4°C. Subsequently, protein G-agarose beads or PBS was added, as indicated, and the mixture was further incubated overnight. After a short centrifugation to pellet the beads, the supernatants were added to UT7 cells at a multiplicity of infection of 500 DNA-containing particles per cell and incubated at 37°C for 4 days. Cells were fixed and stained as specified in Materials and Methods and visualized under a fluorescence microscope. A representative field is shown. (B) Cells showing specific B19 immunofluorescence staining indicative of infection. (C) Cells infected with B19 in the presence of increasing concentrations of MAb 1418-1 (VP1u). (D) Attachment of B19 to UT7 cells in the presence or absence of MAb 1418-1 (VP1u). Cells were infected as specified above in the presence or absence of MAb 1418-1 and incubated at 4°C for 1 h to allow virus attachment. Subsequently, cells were washed four times with PBSA and the amount of cell-associated viral DNA was quantified by real-time PCR as described in Materials and Methods. PG, protein G-agarose beads.