RECEPTOR-BINDING AND INTERNALIZATION OF A WATER-SOLUBLE (1-]3)-BETA-D-GLUCAN BIOLOGIC RESPONSE MODIFIER IN 2 MONOCYTE-MACROPHAGE CELL-LINES

Glucan phosphate, a water-soluble, chemically defined (1-->3)-beta-D-g lucan biologic response modifier, has been reported to exert anti-seps is activity and accelerate wound healing. In this study we describe th e specific binding of glucan phosphate to human and murine monocyte/ma crophage cell lines, U937 and J774A.1, respectively, At 37 degrees C, equilibrium binding was rapidly achieved, i.e., within 1 min. In U937 cells, binding occurred with an affinity (K-d) of 37 mu M and a B-max of 65 x 10(6) binding sites/cell at 37 degrees C. In J774A.1 cells, gl ucan phosphate bound with an affinity (K-d) of 24 mu M and a B-max of 53 x 10(6) binding sites/cell at 37 degrees 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 vacuoli zation and significantly decreased mitotic activity in glucan phosphat e-treated U937 cells compared with that in untreated cells, Pullulan, a random coil alpha-(1-->4)-(1-->6)linked glucose polymer that served as a control, did not compete for the same binding site as glucan phos phate in either cell line, indicating the specificity of the binding s ite for (1-->3)-beta-D-glucans. We conclude that water-soluble pharmac eutical grade (1-->3)-beta-D-glucan phosphate specifically binds to an d is internalized by U937 and J774A.1 cells.