A Novel Carbohydrate-Glycosphingolipid Interaction between a β-(1–3)-Glucan Immunomodulator, PGG-glucan, and Lactosylceramide of Human Leukocytes

Abstract

The immunomodulator Betafectin® PGG-glucan is a homopolymer of glucose derived from yeast cell walls which has been demonstrated to enhance leukocyte anti-infective activity in vitro and in vivo, without the induction of proinflammatory cytokines. We report here the purification of a PGG-glucan-binding element from human leukocytes and its identification as lactosylceramide, a major glycosphingolipid of neutrophils, which includes the CDw17 epitope. The binding of radiolabeled PGG-glucan to purified lactosylceramide was saturable, specific, and time-and temperature-dependent. Lactosylceramides from human leukocytes were fractionated by high performance liquid chromatography in order to analyze the effect of ceramide structure on binding. A variety of fatty acid chain lengths with varying degrees of unsaturation were found to support binding to radiolabeled PGG-glucan. However, DL-lactosylceramides containing dihydrosphingosine did not bind. Radiolabeled PGG-glucan bound several other neutral glycosphingolipids with a terminal galactose, including galactosylceramide, globotriaosylceramide, and gangliotetraosylceramide. The binding of radiolabeled PGGglucan to lactosylceramide was not inhibited by glycogen, dextran, mannan, pustulan, laminarin, or a low molecular weight ␤-(1-3)-glucan, but was inhibited by high molecular weight ␤-(1-3)-glucans and by a monoclonal antibody to lactosylceramide. Although this glycosphingolipid has been shown in numerous reports to bind various microorganisms, this represents the first report of lactosylceramide binding to a macromolecular carbohydrate.

Pneumocystis carinii Cell Wall β-Glucan Induces Release of Macrophage Inflammatory Protein-2 from Alveolar Epithelial Cells via a Lactosylceramide-mediated Mechanism

“…LacCer has been shown to bind several different bacteria and yeast (41). Recently, LacCer has been demonstrated to bind poly-(1,6)-beta-D-glucopyranosyl-(1,3)-beta-D-glucopyranose glucan, a purified ␤-glucan derived from the cell wall of Saccharomyces cerevisiae (15). The binding of PGG-glucan to LacCer activates a NF-Blike nuclear transcription factor in human polymorphonuclear cells (16).…”

“…CD11b/CD18 possesses one or multiple lectin binding sites on the C-terminal domain of the CD11b/CD18 ␣ subunit capable of interacting with complex carbohydrates (14). Additional studies using leukocytes have further demonstrated that the cell membrane glycosphingolipid, lactosylceramide (CDw17), also interacts with ␤-glucans (15). Interaction of glucans with CDw17 has also been reported to promote enhancement of the oxidative burst response and NF-kB activation of neutrophils (16).…”

Anticlastogenic effect of β-glucan, extracted from Saccharomyces cerevisiae, on cultured cells exposed to ultraviolet radiation

“…Among these effects, notable ones are reduction in cholesterol, antioxidant and anticarcinogenic properties, and prevention of type 2 diabetes (Arvanitoyannis and Van Houwelingen-Koukaliaroglou 2005;Riccardi et al 2005). b-glucans are polysaccharides present in the cell walls of microorganisms (bacteria and fungi) and plants (barley and oats; Cisneros et al 1996;Zimmerman et al 1998).…”

Involvement of Branched Units at Position 6 in the Reactivity of a Unique Variety of β-D-Glucan fromAureobasidium pullulansto Antibodies in Human Sera

“…Host molecules that serve as -glucan receptors have recently been reported, e.g., complement receptor type 3 (CR3) 9) and lactosylceramide (LacCer). 10) More recently, dectin-1 has also been described as a 1,3--glucan receptor. 11,12) It is important to determine the relationship between the structure and receptor-binding ability of -glucans.…”