FIG. 2.

Antibody-dependent enhancement of the American and Asian genotypes of DENV-1 or DENV-2 in human monocytes. (A) DENV ICs were formed with DENV-2 IQT2913, DENV-2 16681, or DENV-1 16007 and serially diluted human monotypic DENV-1 immune serum. The percentages of CD14-positive monocytes infected with DENV-1 (MOI, 2.0) or DENV-2 ICs were determined by a previously described flow cytometry method (6). Open symbols indicate mock infection. DV, dengue virus. (B) The amount of virus released from monocytes after 48 h was measured with directly inoculated Vero cells by flow cytometry, as described previously (6). (C) The amount of virus released from monocytes after 48 h was measured by titrating supernatants in duplicate in a Vero cell plaque assay (11).