Durable normal erythropoiesis in organotypic cultures of guinea pig foetal liver.

U URING the embryonic and fetal development of mammals, erythropoiesis, first localized in the yolk sac, continues in some transitional blood forming organs, such as liver and spleen; only in the second half of the fetal period does erythropoiesis become definitely localized in the bone marrow. The differentiation of erythroid elements is incompletely understood, although extensive work has demonstrated that erythropoiesis is under the control of a hormone ( erythropoietin ) which acts on the primitive stem-cell precursor of the erythroblast. Anoxic and anemic conditions greatly increase the production and consequently the circulatory level of erythropoietin, and routine methods are available for its quantitative estimation in vivo. Culture of erythropoietic tissue cells in vitro is widely employed for several purposes; but most experiments have been carried out with short-term cultures. Anemic plasma’ or purified erythropoietin2 show a favorable action in maintaining or reactivating3 the hepatic erythropoiesis of the mouse fetus in vitro. In experiments with histiotypic cultures,2 the duration and maintenance of erythropoiesis in vitro did not exceed 4 hours. Gallien-Lartigue1’3 cultivated explants of fetal liver for about 10 days utilizing the organotypic technic culture of Wolff and Haffen; but it should be noted that the differentiation of stem-cells into erythroblasts stopped after the fifth day whereas the maturation of erythroblasts into erythrocytes continued a little longer. It was concluded that the stem-cells capable of reacting to exogenous administration of erythropoietin disappear either in consequence of their differentiation into erythroblasts, or that aging and death of the cells occurs in these experimental conditions, presumably due to the lack, in the culture media, of nutritional and hormonal factors necessary for the maintenance and renewal of this particular class of cells. Working with hematopoietic organs of the chick embryo and utilizing the culture method of Wolff and Haffen,4 it has been possible to maintain myeloida and spleen6 erythropoiesis in long-term cultures (12-15 days) under the action of erythropoietin-like factors from the embryonic liver. Therefore it seemed interesting to test the action of anemic serum on the erythropoietic fetal liver of another species of mammal (guinea pig), with the object of prolonging normal erythropoiesis in vitro; we believe that a normal