Immunology, virology, and epidemiology of flaviviruses and other emerging viruses

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications & trials

Abstract

1. Antigenic evolution of dengue viruses over 20 years. An exceptional feature of the four dengue virus serotypes (DENV1-4) is that they can use preexisting heterotypic antibodies to infect Fc receptor-bearing immune cells, leading to higher viral load and immunopathological events that augment disease. If DENV1-4 are evolving antigenically, changes are expected to be most evident in a single highly endemic geographic location where strains interact directly with immunity derived from other currently or previously circulating strains. We tracked the antigenic dynamics of each DENV serotype using 1,944 sequenced isolates from Bangkok, Thailand between 1994-2014 (n=348) in comparison to regional and global DENV antigenic diversity (n=64 strains). Antigenic data were fitted using antigenic cartography and antigenic dynamics modeled with generalized additive models. Over the course of 20 years, the Thailand DENV serotypes gradually evolved away from one another. However, for brief periods, the serotypes became more similar, with corresponding changes in epidemic magnitude. We also found that antigenic evolution differed within a genotype versus during a major genotype replacement event. Within genotype for DENV1, DENV2, and DENV4, major outbreaks correlated with evasion of homotypic immunity. In the case of DENV3, antigenic similarity to other serotypes as well as to earlier DENV3 strains was associated with the lowest DENV3 incidence, potentially indicating selection for DENV3 strains that escaped both homotypic and heterotypic immunity. Our findings support a previous phylogenetic study of DENV in Thailand which showed that clade replacements are associated with declining incidence, suggesting immunological pressure imposed by co-circulating serotypes, rather than population bottlenecks, help govern replacement events. The balance between cross-protection and antibody-dependent enhancement has been posited to explain the phylogenetic distance between DENV1-4 and may help explain the more bounded nature of DENV antigenic evolution we observe here compared to other well-studied antigenically variable viruses. This work constitutes the most comprehensive dataset to date to explore hypothesized evolutionary tradeoffs for DENV and more broadly among antigenically interacting serotypes, with potentially important insights for identifying the determinants of viral antigenic evolution and informing virus surveillance and vaccine evaluation. 2. Beneath the surface: Amino acid variation underlying two decades of dengue virus antigenic dynamics in Bangkok, Thailand. Antibody levels are an important predictor of DENV infection risk and pathogenicity. Thus, identifying how sequence variation is associated with neutralization of distinct strains is important for vaccine design and development. Previous studies have primarily focused on the envelope protein, the main target of DENV-specific neutralizing antibodies. However, the role of other structural and non-structural proteins in modulating DENV antigenic properties is poorly understood. We used full genome sequences to identify the effects of residue variation in all 10 DENV proteins on antigenic differences among 348 DENV1-4 collected from individuals living in Bangkok, Thailand (1994-2014). In addition to identifying residues in the envelope protein within the epitopes of known neutralizing antibodies, we also identified residues with antigenic effects in other regions of the envelope protein, some neighboring antibody binding sites but also in the stem/anchor region, which was recently shown to become exposed at body temperature. When we examined residues outside of the envelope, only nonstructural protein 2A had significant antigenic signal beyond what was associated with linkage with the envelope. The nonstructural protein 2A is involved in orchestrating virus formation, suggesting it may have a role in modulating the assembly of the infectious virion. Our findings suggest it is important to investigate viral determinants in both structural and non-structural proteins to identify the antigenic determinants of DENV1-4.