Stimulating Human Granulocytic Colony-Forming Cells, Precursors of These Cells, and Primitive Erythroid Progenitors: Some Apparent Nonidentities

The relationship between molecules having granulocyte colony-stimulating activity (G-CSA), erythroid burst-promoting activity (E-BPA), and activity promoting increase in the number of granulocytic progenitors in liquid culture ( GPA) was explored in conditioned medium from human leukocytes (HLCM) and human placenta (HPCM). As tested on human hemopoietic progenitors in culture. G-CSA eluted from Sephadex G100 as a single peak with apparent molecular weight of 25,000, separating partially from EBPA and GPA, which both had an apparent molecular weight of 45.000. All three activities eluted together from hydroxyapatite at low molarity phosphate. Their charge properties were also similar and all three electrofocused in flat gel beds in the pH range near 5.4. On both hydroxyapa-