title: A (1-->3)-beta-D-linked heptasaccharide is the unit ligand for glucan pattern recognition receptors on human monocytes.
abstract: Glucans are fungal cell wall polysaccharides which stimulate innate immune responses. We determined the minimum unit ligand that would bind to glucan receptors on human U937 cells using laminarin-derived pentaose, hexaose, and heptaose glucan polymers. When U937 membranes were pretreated with the oligosaccharides and passed over a glucan surface, only the heptasaccharide inhibited the interaction of glucan with membrane receptors at a K(d) of 31 microM (95% CI 20-48 microM) and 100% inhibition. However, the glucan heptasaccharide did not stimulate U937 monocyte NFkappaB signaling, nor did it increase survival in a murine model of polymicrobial sepsis. Laminarin, a larger and more complex glucan polymer (M(w) = 7700 g/mol), only partially inhibited binding (61 +/- 4%) at a K(d) of 2.6 microM (99% CI 1.7-4.2 microM) with characteristics of a single binding site. These results indicate that a heptasaccharide is the smallest unit ligand recognized by macrophage glucan receptors. The data also indicate the presence of at least two glucan-binding sites on U937 cells and that the binding sites on human monocyte/macrophages can discriminate between glucan polymers. The heptasaccharide and laminarin were receptor antagonists, but they were not receptor agonists with respect to activation of NFkappaB-dependent signaling pathways or protection against experimental sepsis.
authors.affiliation: Department of Surgery, James H. Quillen College of Medicine, East Tennessee State University, Johnson City 37614-1708, USA.
authors.forename: E
authors.initials: E
authors.lastname: Lowe
authors.forename: P
authors.initials: P
authors.lastname: Rice
authors.forename: T
authors.initials: T
authors.lastname: Ha
authors.forename: C
authors.initials: C
authors.lastname: Li
authors.forename: J
authors.initials: J
authors.lastname: Kelley
authors.forename: H
authors.initials: H
authors.lastname: Ensley
authors.forename: J
authors.initials: J
authors.lastname: Lopez-Perez
authors.forename: J
authors.initials: J
authors.lastname: Kalbfleisch
authors.forename: D
authors.initials: D
authors.lastname: Lowman
authors.forename: P
authors.initials: P
authors.lastname: Margl
authors.forename: W
authors.initials: W
authors.lastname: Browder
authors.forename: D
authors.initials: D
authors.lastname: Williams
mesh_terms: D000818:Animals; D001665:Binding Sites; D004305:Dose-Response Relationship, Drug; D005936:Glucans / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D008297:Male; D051379:Mice; D008812:Mice, Hairless; D008813:Mice, Inbred ICR; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D011134:Polysaccharides / Q000276:immunology / Q000378:metabolism* / Q000494:pharmacology; D011485:Protein Binding; D011971:Receptors, Immunologic / Q000187:drug effects / Q000378:metabolism*; D018805:Sepsis / Q000276:immunology; D020298:U937 Cells
chemical_list: D005936:Glucans; D008024:Ligands; D016328:NF-kappa B; D011134:Polysaccharides; D011971:Receptors, Immunologic; C045268:beta-glucan receptor; C008247:laminaran