Antibody-mediated enhancement of dengue virus infection in mouse macrophage cell lines, Mk1 and Mm1.

Antibody-mediated enhancement of dengue type 2 virus (D2V) replication in murine macrophage cell lines (Mk1 and Mm1) was studied. While both Mk1 and Mm1 supported D2V replication in the absence of enhancing antibodies, virus production was enhanced when both cell lines were inoculated with D2V in the presence of dengue type 1 virus (D1V)-hyperimmune rabbit IgG, D1V-hyperimmune mouse ascitic fluids, or D2V-hyperimmune mouse ascitic fluids at subneutralizing concentrations. The enhancement ratios were greater in Mk1 than in Mm1. Type-specific neutralizing monoclonal anti-D2V antibody also mediated D2V replication enhancement in Mk1 to the same extent as mediated by three other enhancing antibodies described above. In contrast, however, the same monoclonal antibody mediated only a slight and smaller magnitude of D2V replication enhancement in Mm1 than did the other enhancing antibodies. Fluorescent antibody observations revealed that virus replication enhancement in both Mk1 and Mm1 was due primarily to an increase in the numbers of virus-infected cells. D2V infection enhancement in Mk1 by the anti-D2V mouse ascitic fluids at a dilution showing nearly 50% plaque-reduction activity was markedly suppressed by addition of complement to the inocula, whereas that by the monoclonal antibody, which has been identified as mouse IgG1, was not. Phagocytoses of tritiated thymidine-labeled bacteria by Mk1 and Mm1 were also enhanced when the bacteria had been opsonized with antibody. The phagocytosis enhancement ratios were again greater in Mk1 than in Mm1.