Factors regulating yolk sac hematopoiesis in diffusion chambers: various types of sera, cyclophosphamide, irradiation and long-term culture.

A series of studies were conducted using suspensions of murine 10 1/2 day yolk sac cells, cultured in diffusion chambers (DC), to evaluate the effects of several variables on cell growth and differentiation. The variables evaluated were: treatment of chamber recipients with cyclophosphamide (Cy) or sublethal total body irradiation (TBI), culture medium supplementation with different sera, and long-term culture. The growth of cells in Cy- and TBI-groups was parallel to that of the control group (C) until day 7 of culture. Thereafter, cells in the chambers of each group proliferated at a different rate. Whereas, cell growth in Cy-hosts was significantly greater than in C-hosts, growth of TBI-hosts was less than that in C-hosts. Horse serum supported chamber cellularity better than syngeneic mouse serum or fetal calf serum. Long-term cultures showed an increase in cell numbers until day 56, followed by a steady decrease to day 70, reaching a new level that was maintained until day 98. By day 14 of culture, and throughout the long-term culture study, there was no difference in the pattern of differentiation of DC cultured yolk sac cells. Regardless of the type of host treatment or culture medium the cells harvested were macrophages, plasma cells and lymphocytes.

Cell growth and differentiation of murine extra-embryonic fetal and adult hematopoietic tissues in diffusion chamber cultures.

Studies were conducted with diffusion chambers (DC) filled with cell suspensions from different CF1 murine hematopoietic tissues: adult peripheral blood; adult tibial marrow; day 17-5 of gestation fetal liver, spleen and thymus; day 14-5 gestation fetal liver; day 10-5 of gestation yolk sac. After an initial decrease in DC cell numbers on day 2 of culture, growth of each cell group continued, but, at different rates. ATM had the highest growth ratio and FT-D17-5(2) had the lowest. The growth rates for APB and FL-D17-5 were similar. FS-D17-5 and FL-D14-5 cultures did not recover from the day 2 values (i.e. FL-D14-5 DC values on day 13-14 of culture were half that recorded on day 2). The YS-D10-5 DC cell numbers continued to increase throughout the 14 days of study. The profile of cellular elements from the DCs did not reflect the original cell suspensions. The predominant cell type recovered from peripheral blood cultured for 14 days was the macrophage. By day 10-14 of culture, the populations of cells harvested from the fetal tissue DC groups were similar to that of tibial marrow. Both proliferative and mature granulocytes, and macrophages were the predominant cell types. The yolk-sac pattern of cytodifferentiation recorded on day 7-14 was unlike that of the other groups. These DC cultures were comprised of mainly macrophages and plasma cells.

Thrombocytotic suppression of megakaryocyte production from stem cells.

Megakaryocytopoiesis in the spleens of lethally irradiated mice transplanted with marrow cells was suppressed by platelet transfusions. In one group of experiments, animals were irradiated and transfused with bone marrow cells on day O. They were then given either no treatment, platelets, platelet-poor plasma, or saline on days 0, 2, 4, 6, and 8, and then were sacrificed on day 10. Megakaryocytes per section in the spleens of mice receiving platelets were 24%-48% of the values in the groups given plasma, saline, or bone marrow only. The number of pure megakaryocyte colonies was also diminished by platelet hypertransfusion. Another experiment examined the effect of platelets or plasma administered on days 1 and 2 or days 6 and 7 after irradiation and bone marrow transfusion. Hypertransfusion on days 6 and 7 was as effective in suppressing megakaryocytopoiesis as hypertransfusion every other day for 10 days. Animals given platelets or plasma only on days 1 and 2 did not have any significant change in their megakaryocyte number. These results implied that committed megakaryocyte precursors were more sensitive to inhibition by increased platelet levels than pluripotential stem cells. Further experiments with plethoric animals indicated that different levels of erythropoietin did not account for the effects of platelet hypertransfusion. The findings could be explained by inhibition of cell proliferation or of differentiation of megakaryocyte precursors by increased platelet levels.

Fetal hemopoiesis in diffusion chamber cultures. III. The effect of neutropenia.

Proliferation and differentiation of granulocytes, macrophages, and both myeloid committed (CFC) and pluripotent (CFU) stem cells in diffusion chamber (DC) cultures of fetal liver were studied in order to evaluate the role of circulating humoral factors in the control of fetal myelopoiesis. When DC with fetal liver cells were implanted into mice rendered neutropenic by pretreatment with cyclophosphamide, more granulocytes and CFC were produced through day 10 as compared to DC implanted into saline pretreated control hosts. A difference in CFU recovery from fetal liver suspensions grown in DC implanted into neutropenic and control hosts was not seen until day 10. Serum CSF concentrations were increased in neutropenic as compared to control host mice 2 and 3 days after implantation of DC. Levels of serum inhibitors of colony growth showed marked variability but, in general, were similar in both groups. These data provide evidence that fetal CFC and fetal myelopoiesis are influenced by a circulating humoral factor present in neutropenic serum. CSF may be the factor, although the data presented in this paper do not establish this with any certainty.

The effects of acute bleeding on acid-base balance erythropoietin (Ep) production and in vivo P50 in the rat.

The mechanism of erythropoietin (Ep) production after acute haemorrhage has been thought to be due to a reduction in blood volume and tissue perfusion leading to tissue hypoxia. In the present study we have evaluated the effect of acute haemorrhage in the rat on the acid-base status, the red cell affinity for oxygen in vivo, and Ep production. Within a few hours after acute blood loss there was a respiratory alkalosis with an increase in blood pH, a decrease in pCO2 and an increase in the red cell affinity of Hb for oxygen in vivo that was temporally related to an increase in Ep production. Within 24 h after the acute haemorrhage, the blood pH AND PCO2, red cell affinity for oxygen in vivo, and Ep level returned towards normal. The decrease in in vivo red cell affinity for oxygen was associated with an increase in red cell 2,3-DPG levels and a decrease in Ep production.

Growth of mouse yolk sac cells cultured in vivo.

The proliferation and differentiation of yolk sac cells from 10 1/2-day-old mouse embryos were studied in diffusion chambers implanted into syngeneic and allogeneic hosts. The most striking observation was the appearance, proliferation and predominance of immature and mature plasma cells. The data suggested that the differentiation into plasma cells and the rate of growth of yolk sac cells cultured in vivo may be dependent on the genetics of the strain of mouse and host. This demonstration of differentiation of plasma cells from yolk sac cells cultured in vivo adds further information to the origin and ontogeny of potentially immunocompetent cells.

Effect of a congenital defect in hemopoiesis on myeloid growth and the stem cell (CFU) in an in vivo culture system.

W/Wv mice with congenitally defective CFU proliferation and their normal, congenic littermates were used as hosts for diffusion chamber (DC) implants. CFU growth in implanted allogenic CF1, or congenic +/+ marrow was significantly greater in W/Wv than in control hosts. When W/Wv mice were "cured" of their hemopoietic defect, CFU proliferation in the DCs decreased, but not to the control level. These observations have provided evidence for humoral control of CFU growth related to a genetic stem cell defect. Diffusion chamber myelopoiesis was also enhanced in W/Wv hosts. In comparison with their congenic controls, W/Wv mice were neutropenic and had decreased numbers of marrow myeloid elements. Thus, a humorally mediated feedback related to a defective myelopoiesis in the hosts might have accounted for increased DC myelopoiesis. However, a "spillover" effect from increased stem cell growth has not been excluded.

Erythroid differentiation of fetal, newborn and adult haemopoietic stem cells.

Erythroid regeneration was studied in lethally irradiated mice given transplants containing equivalent numbers of haemopoietic stem cells (i.e. CFU) from fetal liver, neonatal marrow or adult marrow. Adult marrow was taken from normal control mice, whose CFU for the most part were not in active cell cycle, as well as from phenylhydrazine-treated groups whose CFU were in similar state of proliferation (i.e. approximately 40-50% in DNA SYNTHESIS) AS THOSE DERIVED FROM FETAL LIVER AND NEONATAL MARROW. Splenic and femoral radioiron (59Fe) incorporation were measured at intervals after transplantation and were found to begin earliest in mice given fetal liver, then in animals given neonatal marrow and latest in recipients of adult marrow. Peripheral reticulocytes showed a similar pattern of recovery. The data reported herein suggest that the differences in erythroid regeneration evoked by transplants of fetal liver, neonatal marrow or adult marrow, are not solely attributed to the degree of proliferation in the pluripotential stem cell compartment. These data may, however, suggest a shorter doubling time for cells comprising the fetal and newborn committed erythroid compartments.

Fetal hemopoiesis in diffusion chamber cultures: II. Cell proliferation and differentiation.

The growth and differenciation of hemopoietic cells from murine fetal liver (FL) and adult bone marrow (ABM) in diffusion chambers (DC) implanted into normal CF1 mice were evaluated. Initially FL suspensions were approximately 90% erythrocytic, but after 4 days in DC implanted into either normal or phenylhydrazine (anemic) pretreated hosts, growth was essentially restricted to the granulocyte-macrophage cell types. The number of in vitro colony forming cells (CFC), as assayed in a double layer soft-agar technique was determined after varying periods of growth in DC of both ABM and FL. Both groups showed a progressive decline in CFC number. FL and ABM CFC generated the same proportion of different morphologic types of soft agar colonies. After 7 days of DC culture, there was a decrease in the proportion of macrophage colonies from both groupes. During DC culture the ratio of clusters (3-50 cells to colonies progressively increased in both groups suggesting a parent-progeny relationship between CFC and cluster forming cells. The results of these studies provide further evidence that the environment rather than properties intrinsic to murine stem cell determines the pattern of proliferation.

Fetal hemopoiesis in diffusion chamber cultures. I. The pattern of pluripotent stem cell growth.

The growth pattern of fetal liver (FL), normal adult bone marrow (NABM) and regenerating (post Velban treatment) adult bone marrow (RABM) colony forming units (CFU) cultured in diffusion chambers (DC) was studied. When twenty CFU were implanted into DC the recovery of CFU after 4 days with FL, NABM or RABM was 133 +/- 7, 19 +/- 2 and 34 +/- 2 CFU, respectively. The transplantation fraction of CFU from NABM decreased from 10-4% on day 0 to 6-9% on day 4; that of FL did not change from the initial 6-2%. The growth rate of CFU derived from FL was substantially greater than that from NABM. The relative growth of FL and RABM CFU was clearly inhibited when the concentration of cells cultured was increased. Spleen colonies from FL cells before culture were larger (P less than 0-005) than colonies from NABM but after 7 days of culture there was no difference between the two groups. Histological examination of spleen colonies showed that after DC culture FL and NABM CFU were differentiating along the three normal pathways. These data suggest that intrinsic differences exist between fetal and adult stem cells in the in vivo diffusion chamber culture system.

Hydroxyurea-induced erythroid differentiation.

Hydroxyurea, a cytotoxic agent which destroys cells in DNA synthesis, has been shown to evoke the differentiation of a small number of hemopoietic precursor cells in the erythroid series of erythropoietically suppressed hypertransfused mice. This effect does not appear to be mediated by erythropoietin (EP) since the simultaneous injection of anti-EP did not alter this response.

Tolerance to the granulocyte-releasing and colony-stimulating factor elevating effects of endotoxin.

Injection of Salmonella typhosa endotoxin into either CF1 or C57bl/6J mice leads to prompt increases in serum colony-stimulating factor (CSF). Repeated injections of endotoxin result in a dose-related hyporesponsiveness or tolerance to this effect. Tolerance is seen after either intravenous (i.v.) or intraperitoneal (i.p.) routes of administration or challenge and occurs after one to two preinjections. Cross-tolerance to heterologous endotoxin (Escherichia coli) was also shown. This cross-tolerance is complete immediately after cessation of preinjections, but partial at later time intervals. Levels of a serum inhibitor of colony growth were decreased in tolerant mice, although this decrease is not statistically significant. Tolerant mice injected with endotoxin release granulocytes from the bone marrow normally, in spite of the absence of a CSF response. This suggests that neutrophil releasing activity (NRA) and CSF are separate entities. A marked marrow granulocytic hyperplasia develops after 7 or 20 days of endotoxin injections, despite the tolerance to the CDF-elevating effect of endotoxin. This granulocytic hyperplasia could still be mediated by serum CSF increases. A negative medullary feed-back secondary to the repetitive release of marrow granulocytes, however, is an equally plausible mechanism for the stimulation of granulocyte production. It is also possible that the decrease in serum inhibitors played a role in the sustained increase in granulopoiesis seen here.

Effects of vincristine on normal and stimulated megakaryocytopoiesis in the rat.

Vincristine was given to rats in which thrombocytopoiesis was either normal or acutely or chronically stimulated by injections of heterologous antiplatelet serum. A single dose of 0.3 mg/kg was given intravenously. The drug produced an early and a delayed megakaryocytopenia suggesting that it was toxic to differentiated megakaryocytes as well as to proliferating stem cells. The results support the hypothesis that vincristine-induced thrombocytosis may be due to homeostatic adjustments which, in turn, are activated as a result of drug-induced cytotoxicity.