At day 8 postchallenge, mean titers remained consistent at 151

At day 8 postchallenge, mean titers remained consistent at 151.7 (95% CI, 124.7 to 184.6). significantly better than they blocked GII.2.2002, GII.2.2008, and GII.2.2010, suggesting that blockade epitopes within the GII.2 strains have evolved in the past decade. To potentially map these epitope changes, we developed mouse monoclonal antibodies (MAbs) against GII.2.1976 VLPs and compared their reactivities to a panel of norovirus VLPs. One MAb had broad cross-genogroup EIA reactivity to a nonblockade, linear, conserved epitope. Six MAbs recognized conformational ATR-101 epitopes exclusive to the GII.2 strains. Two MAbs recognized GII.2 blockade epitopes, and both blocked the entire panel of GII.2 variants. These data indicate that the GII.2 strains, unlike the predominant GII.4 strains, have undergone only a limited amount of evolution in blockade epitopes between 1976 and 2010 and indicate that the GII.2-protective component of a multivalent norovirus vaccine may not require frequent reformulation. == INTRODUCTION == Noroviruses (NoVs) are the leading cause of viral acute gastroenteritis globally, resulting in over 20 million cases annually in the United States alone. Worldwide, an estimated 200,000 deaths occur each year in developing countries among children under age 5 (1,2). Young children, the elderly, and the immunocompromised are the most susceptible populations to complications arising from norovirus infection (35). With an infectious dose of as few ATR-101 as 20 viral particles, large quantities of viral shedding, and resistance to many chemical disinfectants, noroviruses have been referred to as the perfect human pathogen (6). The onset of symptoms occurs 10 to 24 h following exposure, and the duration of severe gastroenteritis resolves after 24 to 48 h in most cases (7), but there are instances of chronic infection, primarily ATR-101 in immunocompromised individuals (810). Prevention of transmission is complicated by the fact that not all infected individuals are symptomatic, and viral shedding can occur for weeks after symptoms have resolved (1). Members of the familyCaliciviridae, noroviruses are 7.5-kb positive-sense, single-stranded RNA viruses that are structurally composed of three open reading frames (ORFs). ORF1 encodes the nonstructural proteins, including the RNA-dependent RNA polymerase (RdRp). ORF2 and ORF3 encode the major (VP1) and minor (VP2) structural proteins, respectively (11,12). The sequence of ORF2 is used to classify noroviruses; sequence identity of >85% corresponds to the strain, 56.2 to 85% to the genotype, and 38.6 to 55% to the genogroup (12). Genogroup I (GI) and GII strains cause almost all human NoV infections. Within GI and GII, there are currently 31 different genotypes (13), although enhanced outbreak investigation continues to expand the number of identified NoV genotypes. Structurally, the major capsid protein is composed of the shell (S) domain, and the protruding (P) domain, which is further divided into the P1 and P2 subdomains. Ninety copies of dimerized S domain make up the icosahedral shell. The P1 subdomain forms a stalk rising from the shell, while the P2 subdomain forms the tip of the protrusion of the capsomere and ATR-101 is responsible for histo-blood group antigen (HBGA) binding and a majority of identified antibody recognition sites (1417). The P2 subdomain of GII.4 NoVs is under selective pressure and subsequently is hypervariable. Changes in the P2 subdomain result in loss of VLP reactivity with potentially neutralizing blockade antibodies and correlate with the emergence of new, antigenically distinct, GII.4 strains. Additionally, P2 amino acid changes have been shown to influence HBGA binding of GII.4 strains, potentially modulating population susceptibility. While immune escape and variable HBGA binding are well documented for GII.4 NoV strains, the impact of viral evolution on other NoV genotypes is not well characterized. GII.4 strains, which cause a majority (70 to 80%) of NoV outbreaks, have undergone an 9% amino acid substitution rate in the capsid protein sequence over 12 years (1823). In comparison, GII.2 strains cause about 8% of NoV infections KSR2 antibody and have only 2.6% amino acid diversity in the GII.2 capsid over a similar time frame (4). Harris et al. (4) have proposed that the evolution in the capsid.