dHisto-blood group antigens (HBGAs) are important binding factors for norovirus infections. We show that two human milk oligosaccharides, 2=-fucosyllactose (2=FL) and 3-fucosyllactose (3FL), could block norovirus from binding to surrogate HBGA samples. We found that 2=FL and 3FL bound at the equivalent HBGA pockets on the norovirus capsid using X-ray crystallography. Our data revealed that 2=FL and 3FL structurally mimic HBGAs. These results suggest that 2=FL and 3FL might act as naturally occurring decoys in humans. Mothers' milk has long been seen as a great source of infant nutrition and protection against a large number of pathogens. Human milk oligosaccharides (HMOs), the third-mostabundant (10 to 15 g/liter) components of human milk, are thought to be in part accountable for these health benefits (1). HMOs are unconjugated complex glycans, and more than 200 isomers are known. HMOs consist of combinations of different monosaccharide building blocks, including fucose, glucose, galactose, N-acetylglucosamine, and the sialic acid derivative N-acetylneuraminic acid. HMOs have been demonstrated to protect against human noroviruses, rotavirus, and certain bacteria (reviewed in reference 2).Human noroviruses are also known to interact with histoblood group antigens (HBGAs), and the interaction is thought to be important for infection (3-6). HBGAs can be found as soluble antigens in saliva and are expressed on epithelial cells. HBGAs consist of monosaccharide building blocks similar to those of HMOs, and at least nine different HBGA types have been found to interact with human norovirus (7-12). HMOs are thought to act as a "receptor decoy" for certain pathogens, since HMOs and HBGAs mimic each other structurally. However, little is known about how HMOs block norovirus infections. One study found that human milk was able to block genogroup I genotype 1 (GI.1) and GII.4 norovirus strains from binding to saliva samples (13). A follow-up study suggested that certain HMOs might compete with the HBGA binding sites on the GI.1 and GII.4 norovirus capsid (14). Despite the fact that human noroviruses are the dominant cause of acute gastroenteritis, there are still no suitable antivirals or vaccines commercially available.In this study, we analyzed the ability of two HMOs, i.e., 2=-fucosyllactose (2=FL) and 3-fucosyllactose (3FL), to block GII.10 norovirus virus-like particles (VLPs) from binding to HBGAs (Fig. 1A). A slightly modified blocking enzyme-linked immunosorbent assay (ELISA) was developed using both porcine gastric mucin type III (PGM) and human saliva (A and B types) (3, 15). The PGM sample was confirmed to contain a mixture of A and H types using specific anti-HBGA monoclonal antibodies (data not shown).The GII.10 VLPs were expressed and purified as previously described (16). The untreated VLPs were first examined for binding to PGM and saliva samples using a direct ELISA. Maxisorp 96-well plates were coated with 100 l per well of 10 g/ml PGM for 4 h at room temperature. The saliva samples were processed in a si...

Group B Streptococcus (GBS) cell walls potently activate phagocytes by a largely TLR2-independent mechanism. In contrast, the cell wall component lipoteichoic acid (LTA) from diverse Gram-positive bacterial species has been shown to engage TLR2. In this study we examined the role of LTA from GBS in phagocyte activation and the requirements for TLR-LTA interaction. Using cells from knockout mice and genetic complementation in epithelial cells we found that highly pure LTA from both GBS and Staphylococcus aureus interact with TLR2 and TLR6, but not TLR1, in contrast to previous reports. Furthermore, NF-κB activation by LTA required the integrity of two putative PI3K binding domains within TLR2 and was inhibited by wortmannin, indicating an essential role for PI3K in cellular activation by LTA. However, LTA from GBS proved to be a relatively weak stimulus of phagocytes containing ∼20% of the activity observed with LTA from Staphylococcus aureus. Structural analysis by nuclear magnetic resonance spectrometry revealed important differences between LTA from GBS and S. aureus, specifically differences in glycosyl linkage, in the glycolipid anchor and a lack of N-acetylglucosamine substituents of the glycerophosphate backbone. Furthermore, GBS expressing LTA devoid of d-alanine residues, that are essential within immune activation by LTA, exhibited similar inflammatory potency as GBS with alanylated LTA. In conclusion, LTA from GBS is a TLR2/TLR6 ligand that might contribute to secreted GBS activity, but does not contribute significantly to GBS cell wall mediated macrophage activation.