Alteration of virus entry mode: A neutralisation mechanism for dengue-2 virus

Polyclonal antibodies derived from dengue virus immune sera and 3H5 monoclo nal antibody showed potent neutralisation effect on dengue-2 virus in the p laque reduction neutralisation assay. This study demonstrated that antibodi es present in immune human sera and 3H5 monoclonal antibody neutralised den gue-2 virus by altering the virus entry pathway into cells. In the presence of neutralising antibodies, dengue-2 virus was endocytosed by LLC-MK2 cell s. The endocytosis process involved ruffling of antibody-coated virions by cellular pseudopodia and invagination of cell membrane. This mode of entry is atypical as compared to direct fusion of dengue-2 virus with cell membra ne in the absence of antibody. The virions were internalised in the form of virion-antibody complexes consisting of single or clumps of virions. After 3 minutes of incubation, neutralised virions were detected in cellular ves icles, and signs of intra-endosomal penetration into cytoplasm were not evi dent even after a prolonged incubation of 10 minutes, suggesting that viral uncoating was compromised. Vesicle-bound virions were no longer detected a fter 20 minutes of incubation. In addition, no sign of viral replication wa s detected in cells infected with "neutralised" virions by immunofluorescen ce assay. This indicated that internalised virions had been degraded leadin g to abortive infection. in conclusion, antibodies present in 3H5 monoclona l antibody and human immune sera rendered dengue-2 virus non-infective by n eutralising the viral fusion site and causing alteration of viral entry mod e. Antibodies in immune sera but not 3H5 monoclonal antibody also exerted m inimal inhibitory effect on virus binding and internalisation. J. Med. Viro l. 62:364-376, 2000. (C) 2000 Wiley-Liss, Inc.