HEMOPOIEITC SPLEEN COLONY STUDIES

Abstract

Erythropoietin (ESF) administered to either bone marrow donor or lethally irradiated recipient mice did not alter the number and type of spleen colonies formed. Polycythemia (hypertransfusion) of the irradiated recipient of normal bone marrow completely sup-pressed the appearance of morphologically erythroid spleen colonies without significantly altering the incidence of neutrophilic or eosino-philic or megakaryocytic colonies. Since the effect of polycythemia was completely blocked by exogenous ESF, irradiated mice are pre-sumed to be secreting sufficient ESF for maximal erythroid colony development. The polycythemia-suppressed presumptive-erythroid colonies remained as microscopic foci of undifferentiated cells that could be stimulated to undergo both growth and differentiation by administered ESF. Retransplantation of either erythroid or neutro-philic colonies gave both types of secondary spleen colonies. The percentage of erythroid secondary colonies was slightly but signifi-cantly higher among the progeny of transplanted erythroid primary colonies than among the progeny of transplanted neutrophilic primary colonies. On the basis of these and other results it is postulated that most but perhaps not all colony-forming units (CFU) are pluripotent hemopoietic stem cells whose differentiation into each cell line is determined by different hemopoietic-inductive microenvironments (HIM) in different parts of the spleen. ESF may induce erythroid differentiation of only those CFU under the influence of an erythroid HIM. Alternatively, ESF may stimulate growth and function of only those CFU induced by an erythroid HIM into a state of ESF responsive-ness.