FIG. 6.

Antibody-dependent enhancement of WNV replication in alpaca macrophages. Virus was incubated with IgGs purified from naturally infected (A) or vaccinated/boosted (B) animal sera at concentrations that yielded less than 90% neutralization in PRNT assays. Virus-antibody mixtures were inoculated onto monolayers of alpaca macrophages, and supernatants were collected at 48 h postinoculation. Virus released from infected cells was quantified by plaque assay. Dashed lines represent virus obtained from macrophages inoculated with WNV in the absence of antibody. Symbols are labeled with names or numbers assigned to the alpacas from which serum samples were obtained.