Stimulation of tumor necrosis factor-induced human myelogenous leukemic cell differentiation by high molecular weight PSK subfraction.

The mouse macrophage-like cell line, J774.1, spontaneously released differentiation-inducing factor(s). When these cells were treated with a protein-bound polysaccharide, PSK, significantly higher amounts of differentiation-inducing activity were accumulated in the culture supernatant. PSK directly stimulated human myelogenous leukemic cell differentiation induced by J774.1 conditioned medium or by tumor necrosis factor. Among four subfractions of PSK, only the highest molecular weight fraction (MW greater than 200 kD) exerted such a stimulating effect.