P cell-stimulating factor: biochemical characterization of a new T cell-derived factor.

P cell-stimulating factor (PSF) was produced by activated T cells and supported the in vitro growth of persisting cells (P cells) that are probably mast cell progenitors. PSF was obtained from spleen cells or T cell hybridomas, but only after stimulation by concanavalin A. It was shown to be a glycoprotein sensitive to treatment with trypsin, protease, and 2-mercaptoethanol, but not to chymotrypsin or guanidine hydrochloride. PSF was resistant to heating at 80°C and was precipitated by 50 to 80% saturated ammonium sulphate. As determined by gel filtration, PSF had an apparent m.w. of 29,000 in phosphate buffered saline and 23,000 in 6 M guanidine hydrochloride; the closeness of these figures suggests the structure does not involve noncovalently linked sub-units. PSF showed considerable heterogeneity with respect to charge; activity was present with isoelectric points (pl’s) between 4 and 8. After neuraminidase treatment the charge heterogeneity was reduced considerably, and the activity focused between pl 6 and 8. A similar reduction of charge heterogeneity was observed with PSF that was produced in the presence of tunicamycin. Thus protein glycosylation can account, at least partially, for the charge heterogeneity. PSF bound to the mannose-specific lectins concanavalin A and lentil lectin and partly to the N-acetyl glucosamine-specific wheatgerm agglutinin. In all of these analyses, PSF derived from both spleen cells and monoclonal T cell hybridomas had similar properties.