These data will help to further elucidate potential correlates of safety, which are critically needed to assess efficacy of long term norovirus vaccines. Supplementary Material Supplemental Furniture and FiguresClick here to view.(749K, docx) Acknowledgments. We are grateful to Matthew Jaqua, John Oh, Rachele Cruz, Sandra Martin, and Keenan Williamson of the Oregon Health Expert (OHA) and Catherine Yen (CDC) for coordinating enrollment and data/sample collection. showed seroconversion for IgG (80%), IgA (78%), and blockade antibodies (87%). Salivary IgA levels strongly correlated with increased convalescent serum IgA titers and blockade antibodies. Conclusions. Salivary IgA levels strongly correlated with serum IgA titers and blockade antibodies and remained elevated 3 months after a norovirus outbreak. A single salivary sample collected on day time 14 could be used to identify recent infection inside a suspected outbreak or to monitor human population salivary IgA. Keywords: norovirus, IgA, IgG, salivary IgA, blockade antibodies, immune response, seniors Noroviruses are recognized as the main cause of epidemic and endemic acute gastroenteritis in all age groups worldwide [1C3] and the primary cause of foodborne illness in the U.S. [4]. Noroviruses are genetically classified into genogroups (G) and further subdivided into genotypes. Although viruses within GI and GII can cause infections in humans, GII.4 viruses are responsible for most norovirus outbreaks [5, 6]. Histo-blood group antigens (HBGAs) indicated on intestinal epithelial cells have been identified as putative attachment factors for norovirus. Recombinant virus-like particles (VLPs) have been used as antigens for immunological studies and vaccine development [7]. Natural illness primarily produces a genotype-specific immune response [8C10]. To elicit an immune response broad plenty of to generate cross-genotype blockade Cortisone antibodies, current vaccine candidates include GI.1 and GII.4c VLPs [11]. Volunteers vaccinated with this formulation showed a broad cross-genotype blockade response and neutralization against GII. 4 variant strains that did not circulate at the time of the study, suggesting the vaccine may protect against long term emergent GII.4 strains [12, 13]. Additional information on immune response has been from birth-cohort studies involving children <2 years of age [14] or challenge studies in healthy adults [15C18]. Preexisting norovirus-specific salivary immunoglobulin A (IgA) levels, circulating norovirus-specific immunoglobulin G (IgG) memory space B cells, and the presence of blockade antibodies (antibodies focusing on HBGA epitopes) in serum have been identified as Cortisone correlates of safety against disease [15, 19]. Norovirus-specific salivary IgA levels correlate with serum IgA levels and block binding of norovirus VLPs to HBGAs [20, 21]. However, 75% of outbreaks reported in the United States happen in long-term care facilities (LTCFs), [22] which often result in an increase of hospitalization and mortality rates for adults >65 years old [23]. We previously reported the epidemiological and virological characteristics of 10 norovirus outbreaks in LTCFs [24]. With this manuscript we describe the humoral (IgA, IgG, and blockade antibody) and mucosal (salivary IgA) immune reactions to norovirus using virus-like particles specific to the genotype causing each of these outbreaks. MATERIALS AND METHODS Participant Recruitment Forty-three LTCFs were enrolled in the study from November 2009 through January 2013. Participants were recruited prior to 2 consecutive norovirus months (2010 Cortisone and 2011; baseline; 14 facilities, 370 participants) and when suspected norovirus outbreaks were reported (7 facilities, 114 participants) (Supplementary Number 1). Participants were classified as instances or controls based on medical characteristics specific to norovirus [25] and settings were divided into revealed or nonexposed settings [24]. Demographic characteristics, FRPHE clinical and virological data, and sponsor genetic factors related to this study have been published previously (Supplementary Table 1 and Supplementary info) [24]. Saliva and Serum Collection Baseline saliva samples were collected from 10 facilities between November 2009 and February 2010 (baseline I) and from 14 facilities between November 2010 and February 2011 (baseline II). During norovirus outbreaks, saliva samples and sera were collected from instances and revealed settings. Saliva samples were collected on the day of sign onset or exposure (day time 0) and on days 1C5, 8, 14, 21, 56, 70, and 84, and acute and convalescent sera were collected on day time 0 and 21, respectively. If a specimen could not become acquired on those days, a sample was collected as close as you can to the scheduled day. For nonexposed controls, 1 saliva and 1 serum sample were collected within 7 days after the first symptomatic case in the outbreak was recognized. Virus-Like Particles Norovirus-like particles (VLPs) were kindly provided by Dr Charles Arntzen (Arizona State University or college) and Dr Ralph Baric (University or college of North Carolina). For each serum/saliva sample, only antibodies against the norovirus strain that caused the outbreak were evaluated. Detection of Total IgA and Norovirus-Specific IgA in Saliva Total IgA and norovirus-specific salivary IgA titers were decided using GII.4 Den Haag VLPs for baseline I, GII.4 New Orleans VLPs for baseline II, or the outbreak-specific VLP Cortisone [24]. Briefly, 96-well plates were coated with 1 g/mL anti-human IgA or 1 g/mL VLPs. Two-fold serial Cortisone dilutions.