Identification and Characterization of Antibody-Binding Epitopes on the Norovirus GII.3 Capsid

Abstract

Genotype II.3 (GII.3) noroviruses are a major cause of sporadic gastroenteritis, particularly in children. The greater incidence of GII.3 noroviruses in the pediatric population compared to the adult demographic suggests development of herd immunity to this genotype, possibly as a consequence of limited evolution of immune epitopes. This study aimed to identify and characterize immune epitopes on the GII.3 capsid protein and to determine the level of immune cross-reactivity within the genotype. A panel of seven GII.3 virus-like particles (VLPs), representing norovirus strains isolated during 1975 to 2008, was tested by enzymelinked immunosorbent assay (ELISA) for reactivity with human sera and a rabbit anti-GII.3 strain-specific polyclonal serum generated against the 2008 GII.3 VLP. Immunoprecipitation of protease-digested GII.3 VLPs and sequencing of bound peptides via mass spectrometry were used to locate epitopes on the capsid. Two epitopes were investigated further using Mimotopes technology. Serum binding studies demonstrated complete intragenotype GII.3 cross-reactivity using both human and rabbit serum. Six immunoreactive regions containing epitopes were located on the GII.3 capsid protein, two within each capsid domain. Epitopes in the S and P1 domains were highly conserved within GII.3 noroviruses. P2 domain epitopes were variable and contained evolutionarily important residues and histo-blood group antigen (HBGA) binding residues. In conclusion, anti-GII.3 antibody-binding epitopes are highly cross-reactive and mostly conserved within GII.3 strains. This may account for the limited GII.3 prevalence in adults and suggests that a GII.3 strain may be a valuable inclusion in a multivalent pediatric targeted VLP vaccine. Exploration of norovirus immune epitopes is vital for effective vaccine design. IMPORTANCEThis study represents an important contribution to the understanding of norovirus immunology in a pediatric genotype. The high cross-reactivity and conservation of GII.3 epitopes suggest development of herd immunity against GII.3 and indicate that a GII.3 strain would be a valuable inclusion in a pediatric targeted multivalent vaccine. Immunological understanding of pediatric norovirus strains is important since norovirus vaccines will likely target high-risk groups such as the pediatric population.

Norovirus Epidemiology and Genetic Diversity in Leipzig, Germany during 2013–2017

“…While GII.3 infects a constantly renewed pool of young children, GII.4 repeatedly infects adults, escaping the patient's immune response due to higher evolution rates [46]. Limited evolution in GII.3 epitopes as well as cross-reactivity of antibodies among GII.3 strains was described [48], adding to being an interesting vaccine candidate.…”

Genotypes, Recombinant Forms, and Variants of Norovirus GII.4 in Gipuzkoa (Basque Country, Spain), 2009–2012

“…Strains with GII.3 capsid were almost only detected in children, as it has been described in other countries [28] – [30] . NoV GII.3 circulation was intense in the last decades of the last century [9] , [30] , which, together with high cross-reactivity and limited evolution of GII.3 epitopes, could explain why the incidence of NoV infection is currently scarce in the adult population [28] , [31] . The GII.3 strains detected in Gipuzkoa were found in combination with discordant polymerase genotypes, as previously reported [13] , [28] , [29] .…”

Neutralization of Lipocalin-2 Diminishes Stroke-Reperfusion Injury

“…Fifty-six 15-mer peptides with an overlap of 12 amino acids were commercially synthesized (Mimotopes, Victoria, Australia) to cover the entire LCN2 protein sequence [ 63 ]. These peptides were biotinylated at the N -terminus with a 4-amino-acid linker sequence (SGSG) and were included with an amide group at the C terminus.…”