Eight monoclonal antibodies (MAbs) prepared against the flavovirus Saint Louis encephalitis, dengue 2 and dengue 3 viruses all recognized epitopes on the envelope protein of the prototype flavivirus, yellow fever (YF) virus. Three of these MAbs with flavivirus group-common specificity and two MAbs with a flavivirus-subgroup specificity were found to distinguish wild-type YF viruses from YF 17D-204 vaccine virus, but not from the closely related 17DD vaccine virus nor from the French neurotropic vaccine virus. This pattern of reactivity was seen only with viruses grown in Aedes albopictus C6/36 cells and not with viruses grown in vertebrate cells (SW13 and Vero cells), where all five MAbs recognized epitopes on both wild-type and 17D-204 viruses. Examination of adult A. aegypti mosquitoes infected with the same YF viruses as above gave a different pattern of results to those in C6/36 cells. Thus, epitope expression differs between mammalian and arthropod cells and between arthropod cells in vitro and in vivo. Neutralization tests showed that all five MAbs would neutralize wild-type Asibi virus grown in SW13 cells, but not Asibi virus grown in C6/36 cells, nor 17D-204 vaccine virus grown in either cell type. Therefore, it is concluded that when YF virus is grown in mosquito cells, wild-type virus is antigenically and biologically distinct from the 17D-204 vaccine virus.
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