Receptor Binding and Internalization of a Water-Soluble (1→3)-β-D-Glucan Biologic Response Modifier in Two Monocyte/Macrophage Cell Lines

Document Type

Article

Publication Date

5-1-1996

Description

Glucan phosphate, a water-soluble, chemically defined (1→3)-β-D-glucan biologic response modifier, has been reported to exert anti-sepsis activity and accelerate wound healing. In this study we describe the specific binding of glucan phosphate to human and murine monocyte/macrophage cell lines, U937 and J774A.1, respectively. At 37°C, equilibrium binding was rapidly achieved, i.e., within 1 min. In U937 cells, binding occurred with an affinity (Kd) of 37 μM and a Bmax of 65 × 106 binding sites/cell at 37°C. In J774A.1 cells, glucan phosphate bound with an affinity (Kd) of 24 μM and a Bmax of 53 × 106 binding sites/cell at 37°C. In both cases there was insignificant nonspecific binding. We further demonstrated that bound glucan phosphate cannot be displaced by a 50-fold excess of unlabeled ligand, suggesting internalization of glucan phosphate. Transmission electron microscopy showed significantly increased cytoplasmic vacuolization and significantly decreased mitotic activity in glucan phosphate-treated U937 cells compared with that in untreated cells. Pullulan, a random coil α-(1→4)-(1→6)-linked glucose polymer that served as a control, did not compete for the same binding site as glucan phosphate in either cell line, indicating the specificity of the binding site for (1→3)-β-D-glucans. We conclude that water-soluble pharmaceutical grade (1→3)-β-D-glucan phosphate specifically binds to and is internalized by U937 and J774A.1 cells.

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