Analysis of Archival Sera from Norovirus-Infected Individuals Demonstrates that Cross-Blocking of Emerging Viruses is Genotype-Specific.

ABSTRACT

BACKGROUND: Rapidly evolving RNA viruses, such as human norovirus, generate extraordinary sequence diversity, posing a significant challenge to vaccine design. This diversity coupled with short-lasting natural immunity leads to re-infection throughout one's lifetime. How re-exposure shapes humoral immunity to future norovirus strains remains incompletely understood. METHODS: We profiled the antibody responses following two community gastroenteritis outbreaks with GII.2 and GII.6 noroviruses in 1971. Using diverse VLPs, ELISA, and carbohydrate-blocking assays (surrogate for neutralization), we examined the antibody response at acute and convalescent timepoints following GII.6 infection. RESULTS: Convalescent sera displayed strong homologous blocking, demonstrating a 5-fold increase in GII.6 carbohydrate-blockade over acute samples, and broad blocking of diverse archival and modern GII.6 noroviruses. Convalescent sera displayed limited carbohydrate-blocking of heterotypic VLPs, despite high ELISA binding titers. Select individuals developed broad cross-genotype blockade, but this response was established before the second outbreak. Finally, we applied a novel competitive carbohydrate-blocking assay to demonstrate the epitope-specificity and discrete compartments of the neutralizing response. CONCLUSIONS: Our data show that infection generates narrow, focused immunity directed towards the infecting genotype. We did detect broad cross-blocking in specific individuals, but these responses could be attributed to diverse, genotype-specific antibodies pre-dating GII.6 infection.