A NOVEL CARBOHYDRATE-GLYCOSPHINGOLIPID INTERACTION BETWEEN A BETA-(1-3)-GLUCAN IMMUNOMODULATOR, PGG-GLUCAN, AND LACTOSYLCERAMIDE OF HUMAN-LEUKOCYTES

The immunomodulator Betafectin(R) PGG-glucan is a homopolymer of gluco se derived from yeast cell walls which has been demonstrated to enhanc e leukocyte anti-infective activity in vitro and in vivo, without the induction of proinflammatory cytokines. We report here the purificatio n of a PGG-glucan-binding element from human leukocytes and its identi fication as lactosylceramide, a major glycosphingolipid of neutrophils , which includes the CDw17 epitope, The binding of radiolabeled PGG-gl ucan to purified lactosylceramide was saturable, specific, and time- a nd temperature-dependent, Lactosylceramides from human leukocytes were fractionated by high performance liquid chromatography in order to an alyze 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-lactosylcerami des containing dihydrosphingosine did not bind. Radiolabeled PGG-gluca n bound several other neutral glycosphingolipids with a terminal galac tose, including galactosylceramide, globotriaosylceramide, and ganglio tetraosylceramide. The binding of radiolabeled PGG-glucan to lactosylc eramide was not inhibited by glycogen, dextran, mannan, pustulan, lami narin, or a low molecular weight beta-(1-3)-glucan, but was inhibited by high molecular weight beta-(1-3)-glucans and by a monoclonal antibo dy to lactosylceramide. Although this glycosphingolipid has been shown in numerous reports to bind various microorganisms, this represents t he first report of lactosylceramide binding to a a macromolecular carb ohydrate.