Production of autoinhibitory factors by mouse lymphoma cells in vitro and its relationship to thiol dependence.

Five different kinds of mouse lymphoma cells conditioned culture medium so that it became inhibitory to thiol-dependent cells but not to thiol-independent cells. Conditioning was rapid and appeared to be complete in 1-3 hr. The inhibitory effects could be reversed by concentrations of 2-mercaptoethanol higher than those usually required for growth promotion. Inhibitory factors were concentrated by ultrafiltration and chromatography on Sephadex G-10 which showed their apparent molecular weights to be 300-600. The factors were stable at 100 degrees and to proteases but were inactivated (after reduction) by iodoacetamide, indicating that they may be thiols or disulfides.