EFFECT OF A HEMATOPOIETIC PROMOTING FACTOR DERIVED FROM PORCINE KIDNEY ON THE PROLIFERATION OF MOUSE HEMATOPOIETIC PROGENITOR CELLS IN LIQUID CULTURE

We have partially purified a factor from porcine kidney, hematopoietic -promoting factor (HPF), which enhances granulocyte-macrophage colony- forming units (CFU-GM) and erythropoietic burst-forming unit (BFU-E) c olony formation in the presence of various exogenous colony-stimulatin g factors (CSF) or erythropoietin (Epo) from mouse bone marrow cells. In this paper we examine the combined effects of HPF and/or stem cell factor (SCF) with interleukin-3 (IL-3) and interleukin-6 (IL-6) on the proliferation of primitive hemopoietic progenitor cells in liquid cul tures for 7 or 14 d. The combination of IL-3+IL-6+HPF could not increa se the number of CFU-GM, BFU-E, and day-8 colony forming units in sple en (CFU-S) in the cultures of unfractionated bone marrow cells, while this combination resulted in a marked increase of progenitors in cultu res of c-kit(+) enriched cells. In contrast, expansion of progenitors was observed by IL-3+IL-6+SCF or IL-3+IL-6+SCF+HPF in the culture of b oth unfractionated bone marrow cells and c-kit(+)-enriched cells after 7 d. The number of CFU-GM and BFU-E in the combination of IL-3+IL-6+S CF+HPF for c-kit(+) cells showed the largest increase, 109-fold and 38 -fold respectively after 14 d. These results show that HPF has promoti ng activity on hematopoietic stem cells and acts synergistically with SCF in the early stages of hematopoiesis.