Biological properties of a human urinary protein fraction with burst promoting activity

Urinary proteins from patients with iron deficiency anemia and acquired aplastic anemia were fractionated by chromatography on QAE-Sephadex A-50 and Sephadex G-25. Fractions containing erythroid burst promoting activity (code named regulatory protein RP) were separated from erythropoietin. Mouse bone marrow cells were preincubated for one day in suspension culture, in the presence or absence of RP, transferred to a methylcellulose based system and incubated for six more days with erythropoietin (EPO). It was found that the presence of RP in the preincubation medium had a 2 to 4 fold enhancing effect on subsequent erythroid burst colony formation. However, when RP was added to methylcellulose based cultures simultaneously with EPO, the erythroid burst response was reduced or abolished. Addition of RP to marrow cell suspension cultures increased the number of self replicating, pluripotent (erythroid/granuloid, E/G ratio = 3) spleen colony forming units (CFU-S) found at the end of 2 days incubation 3-5 fold over their number in control cultures incubated without the factor. In marked contrast to this, addition of EPO to the cultures caused an increased persistence of CFU-S with a predominantly erythroid commitment (E/G ratio = 19) and a low self replicating ability, as measured by retransplantation of spleen cells into secondary recipients. These observations are compatible with the presence in RP of a factor, or factors, capable of maintaining the size of certain early precursor cell compartments.