Recognition of Histo-Blood Group Antigen-Like Carbohydrates in Lettuce by Human GII.4 Norovirus

Abstract

Human norovirus (HuNoV) genogroup II genotype 4 (GII.4) strains account for about 80% of the gastroenteritis outbreaks in the United States. Contaminated food is a major transmission vehicle for this virus. In humans, pigs, and oysters, histo-blood group antigens (HBGAs) act as attachment factors for HuNoVs. In lettuce, although the virus-like particles (VLPs) of a GII.4 HuNoV were found to bind to cell wall carbohydrates, the exact binding site has not been investigated. Here, we show the presence of HBGA-like carbohydrates in the cell wall of lettuce. The digestion of lettuce leaves with cell wall-degrading enzymes exposed more binding sites and significantly increased the level of binding of GII.4 HuNoV VLPs. Competition assays showed that both the HBGA monoclonal antibody, recognizing the H type, and plant lectins, recognizing ␣-L-fucose in the H type, effectively inhibited VLP binding to lettuce tissues. Lettuce cell wall components were isolated and their NoV VLP binding characteristics were tested by enzyme-linked immunosorbent assays. The binding was inhibited by pretreatment of the lettuce cell wall materials with ␣-1,2-fucosidase. Collectively, our results indicate that H-type HBGA-like carbohydrates exist in lettuce tissues and that GII.4 HuNoV VLPs can bind the exposed fucose moiety, possibly in the hemicellulose component of the cell wall. IMPORTANCE Salad crops and fruits are increasingly recognized as vehicles for human norovirus (HuNoV) transmission. A recent studyshowed that HuNoVs specifically bind to the carbohydrates of the lettuce cell wall. Histo-blood group antigens (HBGAs) are carbohydrates and are known as the attachment factors for HuNoV infection in humans. In this study, we show the presence of HBGA-like carbohydrates in lettuce, to which HuNoVs specifically bind. These results suggest that specifically bound HuNoVs cannot be removed by simple washing, which may allow viral transmission to consumers. Our findings provide new information needed for developing potential inhibitors to block binding and prevent contamination. Foodborne illnesses constitute a recurring public health burden, with an estimated 9.4 million illnesses and 1,351 deaths annually in the United States (1). Currently, most illnesses (58%) are caused by human noroviruses (HuNoVs), and others are caused by human bacterial pathogens, such as nontyphoidal Salmonella spp. (11%) and Clostridium perfringens (10%) (1). Noroviruses (NoVs) are nonenveloped single-stranded RNA viruses belonging to the Norovirus genus of the family Caliciviridae. NoVs have been classified into five genogroups (GI-GV), and GI, GII, and GIV viruses cause gastroenteritis in humans (2). Each NoV genogroup is further subdivided into several genotypes based on genetic similarities. As a single genogroup, GII currently accounts for about 86% of HuNoV cases (3, 4). HuNoVs have a very low infectious dose, and the 50% infective dose (ID 50 ) was estimated as about 18 viruses and 2,800 genomic equivalents (GEs) (5, 6). Moreover, NoVs are extremely...

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“…Several studies [72,88,89] have found HBGA like glycans on glycoproteins and glycolipids in diverse food sources such as oysters, clams, fruits and vegetables. Recently researchers have also found HBGA-like saccharides on the cell wall of lettuce [90]. ABO group determinants were first discovered in the blood.…”

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