Properties of colony-stimulating and inhibiting activities of chicken serum

Serum obtained from young chicks stimulated with endotoxin contained elevated levels of colony-stimulating activity (CSA). This CSA was partially characterized. Incubation at 65 degrees C (60 min) had no effect on the ability of the CSA to support colony formation by nonadherent cells but reduced 3-4 fold its ability to support colony formation by unfractionated marrow cells. These data suggest that most of the serum activity is due to a heat-labile, adherent cell-dependent factor which does not directly affect the nonadherent granulocyte/monocyte colony-forming cell (GM-CFC). The ability of serum to support colony formation was increased by chloroform extraction. This was evidently due to the presence of inhibitory lipoproteins. The lipoprotein fraction of pigeon serum was found to directly block colony formation. The CSA for nonadherent cells migrated as one peak in the postalbumin region during zone electrophoresis. When electrofocused, heterogeneity was detected but all activity was associated with molecules with isoelectric points between pH 4 and 5. Following sequential fractionation by chloroform extraction, ultrafiltration, zone electrophoresis, isoelectric focusing and gel filtration (Ultrogel AcA 44), the activity was separated from most of the remaining protein. One peak of activity was obtained at the excluded volume.