Elevation of colony stimulating factors in mouse serum after injection of PSK, an antitumor polysaccharide

The level of colony stimulating factors (CSF) in mouse serum was elevated by a single intraperitoneal injection of PSK, a host-mediated antitumor protein-bound polysaccharide obtained from Basidiomycetes. The assay for CSF activity was performed by employing a semisolid methylcellulose culture method using mouse bone marrow cells, and the activity was estimated by an equation well matched with the dose response curve obtained in the CSF assay. A temporary increase of CSF activity within 10 h after the injection of an antitumor polysaccharide, Krestin (PSK) (250-1000 mg/kg) was followed by a fast decline in the activity, but no significant increases were detected in the cases of 62.5 and 125 mg/kg PSK injections. The CSF activity in PSK (500 mg/kg)-treated mouse serum was separated into two active fractions by DEAE ion-exchange chromatography, and both fractions were found to induce colonies comprised of cells with the properties of macrophage in regard to morphology, cytochemistry of non-specific esterase, phagocytic function and expression of Fc receptors on the cell surface. The elevation of the serum CSF level due to administration of so-called host-mediated antitumor agents might be one of the tumor-defense mechanisms in vivo.