The production of differentiation autoinducing activity by WEHI-3B D+ leukemia cells

We studied the differentiation autoinducing activity in WEHI-3B D+ cell-conditioned medium (WCM). After culturing 10(6)/ml WEHI-3B D+ cells in RPMI-1640 medium without fetal calf serum (FCS) for 4 days, the supernatant was collected. The medium, concentrated 50-fold by YM-5 membrane filtration, was fractionated by gel exclusion on Ultrogel AcA44. We evaluated the effect of each of the four fractions on differentiation in WEHI-3B D+ cells by morphological, functional, and cytochemical criteria after adding the fractions to liquid or soft-agar cultures of 10(3) cells in 1 ml RPMI-1640 medium containing 10% FCS; the experimental cultures contained 10% of the fractions, with a control for each without the fraction. The growth of WEHI-3B D- cells in culture was inhibited by the addition of fraction P only (mol. wt. 10,000-20,000 daltons). In these same cultures, the cells were granulocyte-like, strongly positive for naphthol ASD chloroacetate esterase, and had phagocytic activity. Colonies grown in agar culture with fraction P also exhibited a peripheral halo of loosely dispersed cells around a central aggregate. Fraction P contained neither granulocyte colony-stimulating activity nor burst-promoting activity. These results suggest that fraction P contains differentiation autoinducing factor that is different from granulocyte colony-stimulating factor or interleukin 3.