Controlling the production of blood cells

The development since 1966 of a technology for growing stem cells in vitro has provided new insights into the controls of blood cell production. Hematopoietic hormones have been purified and important cellular interactions in hematopoiesis have been defined.

[Differential diagnosis of primary and secondary erythrocytosis by means of in vitro culture of hematopoietic stem cells]

Peripheral blood precursor cells from all of 12 patients with polycythaemia vera (PV) formed hemoglobinized colonies in vitro without addition os was strictly epo-dependent in 30 normals and 8 patients with erythrocytosis of other origin. By addition of 1 U epo/ml to the cultures, colony formation was increased up to 5-fold in PV. Untreated patients with a short history had the highest numbers of such epo-responsive precursor cells. In 3 patients with concomitant myelofibrosis, erythroid in vitro growth was abundant, but scattered, single colonies could hardly be identified and their hemoglobinization was poor. This picture did not change with addition of epo, and hemoglobinization did not improve. In vitro grown colonies in PV had morphological abnormalities as compared to colonies grown from normal precursor cells: all stages of erythroid differentiation and up to 50% necrotic cells were found within single colonies. Scattered colonies contained an excess of large, immature, vacuolated erythroblasts. It is concluded that these functionaland morphological abnormalities of in-vitro erythropoiesis are a reliable indicator of PV. Further, transition to myelofibrosis is recognized by a characteristic growth pattern with decreased epo-responsiveness.

[Renal anemia and its modification by chronic hemodialysis]

The renal anaemia is characterized by a decreased new formation of erythrocytes (deficiency of erythropoetin), by haemolysis (uraemic-toxic influences) and by iron deficiency (decreased resorption of iron, blood losses, infectious-toxic component). In long-term haemolysis the iron deficiency increases, in most cases the haemolysis a little decreases, and a deficiency of erythropoietin is not to be established. However, a slight deficiency of folic acid is frequently observed. Apart from the reduction of the retention of substances normally contained in the urine the therapy consists in iron doses and slight doses of folic acid. Only occasionally blood transfusions are necessary.

[Regulation of the human erythropoietic proliferation pool by the microenvironment (author's transl)]

The Effects of Various Substances in the Culture Microenvironment on the Proliferation of Erythroblasts in vitro were Studied and Evaluated by differential cell and mitosis counting in normal and pathologic bone marrow. The mitotic frequency and maturation correlated directly with the erythropoietin content of the medium and were potentiated on addition of either folic acid, etiocholanolon or cAMP. However, erythroblast proliferation was stimulated independently of erythropoietin concentration when either cobalt, and androgen or an anabolic substance was added to the medium. An iron-deficient medium prevented the maturation of erythroblasts to reticulocytes, thereby rendering erythropoiesis ineffective. The existence of an erythrocyte chalone ineffective. The existence of an erythrocyte chalone or an erythropoietin inhibitor could not be deduced from our experiments since the transformation of pluripotent to erythropoetin-sensitive stem cells is not included. A stimulation of the granulopoietic proliferation pool occurred when serum from patients with either polycythemia vera or after acute blood loss was added to the medium.

Cell cycle time of erythroid cells in mice with normal and stimulated erythropoiesis

The cell cycle time of erythroid cells was determined in normal mice and in polycythaemic mice after stimulation of erythropoiesis by exogenous erythropoietin. The method employed was 3HTdR autoradiography of bone marrow cells. After 21 or 38 hours of administratering the erythropoietin 3HTdR was injected into the animals. The cell cycle time was calculated from the curves of changes in the labelling indices of proerythroblasts and basophilic erythroblasts at one hour intervals. The cell cycle time in normal animals was 8.5 hours. Twenty-two to twenty-five hours after stimulation with 1.5 units of erythropoietin, the cell cycle was 7.8 hours. Thirty-nine to forty-two hours after injection, at the time when the number of nucleated erythroid cells was within normal limits, the cell cycle time was 7.7 hours. Under the used experimental conditions, the cell cycle time of early erythroid cells was not significantly changed in comparison with the values obtained in non-treated animals. This is in contrast to the results reported when extreme stimulation of erythropoiesis with endogenous erythropoietin was used.

Effects of erythrocyte lysate and erythrocyte-conditioned medium on erythroid cells in vitro

A component of erythrocyte-conditioned medium has been shown to inhibit the incorporation of tritiated thymidine into erythroblasts from fetal mouse liver, proliferating in vitro. This component, however, has no detectable effect on the growth of colonies of erythroid cells stimulated to grow in viscous culture media by the hormone erythropoietin. Erythrocyte lysate and preparations of haemoglobin derived from the lysate increase the number and size of the colonies growing in vitro. Results are discussed in terms of possible control mechanisms in erythropoiesis.

Erythroid stem cells in Rauscher virusinfected mice

Using the technique for erythroid colony formation in vitro, bone marrow and spleen cells from NMRI mice were studied after Rauscher virus (RLV) infection. There was a substantial decrease in CFUE concentrations during the first days after infection, this being more pronounced in the marrow than in the spleen. In the marrow values gradually return to and are maintained at control levels, while in the spleen a 40-50-fold increase is seen between days 8 and 18. In normal and RLV infected animals the same dose dependence of CFUE growth for erythropoietin was seen. For normal and RLV infected cells in the absence of erythropoietin there were only very few background colonies. In exhypoxic plethoric mice the increase in CFUE concentration seen in normal mice in the spleen, is delayed by 2-3 days.

In vivo and in vitro effect of bacterial endotoxin on erythroid precursors (CFU-E and ERC) in the bone marrow of mice

Erythropoietin injection raised within 24 hr. the number of CFU-E in the femoral marrow of polycythemic mice by 837 percent. Endotoxin given at 0 to 24 hr. before erythropoietin nearly abolished this CFU-E increase. Endotoxin in the culture medium did not inhibit erythroid colony formation, but in vivo endotoxin suppressed erythropoietin-induced differentiation of proerythroblasts from their precursors. Endotoxin thus suppresses marrow erythropoiesis either by inhibiting transformation of erythroid precursors into CFU-E or by causing the disappearance, perhaps by emigration, of CFU-E from the marrow.

Effect of bleeding on in vivo in vitro colony-forming hemopoietic cells

The effect of bleeding on spleen colony-forming units (CFU-S) and on in vitro colony-forming cells with colony-stimulating factor (CFU-C) and erythropoietin (CFU-E) has been evaluated. The in vivo and in vitro colony-forming cells of the bone marrow show a decrease which for the CFU-E, CFU-C follows a short-lived increase. In the spleen, all progenitor cells assayed have shown a significant and sustained increase.

Effect of cortisol in vitro on haemoglobin synthesis by mouse foetal liver

In cultures of foetal mouse liver, collected at various gestational days, the effect of cortisol was investigated on 59Fe uptake into haemoglobin heme and also on the differentiation of the erythroid stem cells or ERC (erythropoietin-responsive cells) into erythroblasts under the action of erythropoietin. Addition of cortisol to the culture medium did not modify in any way the responsiveness of the cell system to erythropoietin but exerted a sustaining action on the rate of haemoglobin synthesis during the second half of the incubation period. This action was restricted to cultures of 15- to 16-day livers and was particularly obvious in erythropoietin-supplemented samples. This selective effect of cortisol likely concerns only the later types of erythroblasts since after 24 h of incubation the polychromatophilic or orthochromatic stages predominate respectively in samples with, or without, erythropoietin. The timing of these results is discussed in the light of previous findings observed in vivo by other authors in the foetal rat.

Glucocorticoids and evolution of haemopoietic tissue in the liver of the rat foetus

The number of haematopoietic cells per unit of volume decreases after day 18 and falls rapidly until day 21. On day 21 it is reduced by three quarters as compared to the day 17 value. Maternal laparotomy causes, in the 24 h period following the operation, an anticipated and accelerated decrease. This effect is prevented by previous adrenalectomy. After maternal adrenalectomy, rat foetuses submitted to decapitation in utero, and therefore completely deprived of corticosteroids, do not present in their liver the involution of the haematopoietic tissue normally observed in their intact littermates. Cortisol administration restores the normal involution. These results show the importance of the role played by corticosteroids in the regulation of foetal liver hematopoietic function. The evolutions of proportions and frequencies of the different cellular types composing the haematopoietic tissue studied during normal pregnancy and after either overload or deprivation of corticosteroids, suggest that corticosteroids exert their action essentially at two levels of the maturation process. They decrease the ability of self-maintenance of the precursor cell pool and accelerate the maturation of the polychromatophilic cells, resulting in a progressive exhaustion of the haematopoietic tissue.

A complement independent erythropoietic inhibitor acting on the progenitor cell in refractory anemia

An erythropoietic inhibitor was detected in the serum of a patient with refractory anemia. Using an in vitro heme synthesis method, the patient's serum produced tenfold inhibition of erythropoietin-stimulated radioactive iron (Fe59) incorporation into heme of normal human marrow at 72 hours, as compared with AB serum. In a separate experiment the patient's serum produced threefold inhibition, whereas immunoglobulin G (IgG) prepared from the same serum sample produced 12-fold inhibition. To identify the site of action of the inhibitor, serum was tested in a cell culture system whereby human marrow cells, grown in a plasma clot, respond to exogenous erythropoietin with the appearance of nucleated erythroid colonies. Each colony arises from a committed erythroid progenitor. The patient's serum produced a two- or tenfold reduction in the number of colonies from normal human marrow. The effect was also demonstrated on autologous marrow obtained when the patient was in "partial clinical remission". Serum samples obtained at various times during the course of the patient's illness all demonstrated a suppressive effect on colony growth. All serums were heat-inactivated, and total hemolytic complement could not be detected in either culture system. It is concluded that the anemia is due to an inhibitor, probably of IgG class, that acts on the erythroid progenitor cell. The absence of heat-labile complement components in the culture systems suggests that the mechanism is not due to immune cytolysis.

Diamond-Blackfan syndrome: lymphocyte-mediated suppression of erythropoiesis

Peripheral blood lymphocytes from six patients with congenital hypoplastic anemia suppressed erythroid cell formation by normal human bone marrow cells in response to erythropoietin in vitro. The results suggest that the anemia in these children has an immunologic basis.

Effect of serum from leukapheresed mice on myelocytes, promyelocytes and colony-forming cells

Leukapheresis of neutrophil granulocytes in mice increased the myelopoietic activity of their serum. Leukapheresed mouse serum (LMS) caused a threefold increase in the in vitro stathmokinetic index of myeloid precursors. Five to ten minutes of incubation were sufficient to change the colony-forming capacity of mouse bone marrow cells as expressed by the increase in the ratio of granuloid to erythroid cells in spleen colonies. The in vitro stathmokinetic index assay also showed that there are diurnal variations in levels of granulopoietic activity in normal mouse sera. However, at any time of the day, LMS had higher granulopoietic activity.

Studies on the erythropoietic cell system in CBA mice after Rauscher virus infection

Erythropoiesis in CBA mice was studied in Rauscher leukemia virus infected mice using the incorporation of 59Fe into spleen, bone marrow and peripheral blood. Beginning at day 4 an increased uptake into the spleen and a decrease in the bone marrow and the peripheral blood was observed. The increased uptake by the spleen was also found in plethoric mice. The erythropoietin responsive compartment was also enlarged in the spleen of these mice. The The dose-response-curve for erythropoietin was altered 4 days after infection, there was a higher background level of 59Fe incorporation and the response to low doses was better in infected animals. The reticulocytopenia which is usually seen in these mice, was overcome by administration of high doses of erythropoietin. It is concluded that the Rauscher virus acts in a similar manner to erythropoietin, but the erythropoiesis induced is ineffective since the cells do not mature. This maturation deficiency is influenced by administration of exogenous erythropoietin.

Erythroid colony growth in congenital hypoplastic anemia

Four children with congenital hypoplastic anemia (Diamond-Blackfan syndrome) and 30 control children with normal erythropoiesis were studied by a cell culture method in which human marrow, grown in a plasma clot, responds to added erythropoietin (EPO) with the appearance of discrete colonies of nucleated erythroid cells. The colonies arise from EPO-responsive stem cells and are not related to the number of morphologically identifiable marrow erythroids plated. Results of studies on control marrow indicated that without EPO there was little or no colony formation. Increasing EPO doses or nucleated marrow cells per culture resulted in a linear increase in colony numbers. The optimal EPO concentration of 2.5 U/ml yielded a mean of 158 +/- 79 colonies/1 x 10(5) nucleated cells on day 7 of incubation. Even in the absence of recognizable erythroids, marrows of all four patients with anemia grew erythroid colonies. Two patients on no therapy had decreased colony numbers. The other two, on prednisone, had normal numbers. Sera from patients did not inhibit colony formation from either autologous or control marrow. In contrast, serum from an adult with acquired pure red cell aplasia produced striking inhibition of colony growth. It appears that the red cell failure in this disorder is not due to an absence of erythroid stem cells, and a serum inhibitor to erythropoiesis as seen in the acquired disease is unlikely.

Use of cell separation and short-term culture techniques to study erythroid cell development

Cell populations highly enriched for the different stages of erythroid cell maturation were obtained by three sequential operations: harvesting of erythroid cells after induction of erythroid hyperplasia in the spleens of mice, elimination of the more mature erythrocytes by immunologic techniques, and separation of the residual nucleated erythroid cells as a function of size by the velocity sedimentation technique. The resulting cell fractions were studied both directly and after overnight incubation in the presence or absence of erythropoietin. In short-term culture, erythropoietin stimulated proliferation of pronormoblasts and basophilic normoblasts but probably not cells at later stages of differentiation. Erythropoietin also appeared to recruit increased numbers of pronormoblasts. In this experimental system, erythroid cell differentiation was able to proceed in the absence of erythropoietin, but without proliferation of these early erythroid cells. These techniques have provided a model system for the study of erythroid cells at different stages of maturation isolated from a uniform source at one point in time. The morphologic observations indicated that erythropoietin stimulates erythroid cell proliferation at several early stages of the maturation pathway.

Erythroid colony induction without erythropoietin by Friend leukemia virus in vitro

Erythroid colonies could be produced without the addition of erythropeietin in plasma cultures seeded with bone marrow cells from normal C3Hf/Bi mice by exposure of the cells in vitro to medium from a cell line (IS) that continuously produces Friend leukemia virus in culture. The activity in the culture medium was viral rather than erythropoietin-like, since it was sedimentable by high-speed centrifugation and heat labile. Erythroid colonies did not develop when the bone marrow cells exposed to virus-containing medium were from mice genetically resistant to Friend virus. IS culture medium contained both Friend spleen focus-forming and XC-plaque-forming activities. No erythroid colonies were induced when genetically sensitive cells were exposed to a preparation from which the spleen focus-forming activity had been removed, but which contained XC plaque-forming activity in high concentration. Thus the spleen focus-forming component of Friend virus appeared to be responsible for inducing erythroid colony formation without erythropoietin in vitro. Some erythroid colonies were also found in control cultures to which neither virus nor erythropoietin had been added. Reduction in the concentration of fetal calf serum in the culture medium substantially decreased the number of these colonies but had only a minor effect on the number of virus-induced colonies. The number of erythroid colonies produced after 2 days of culture without erythropoietin or fetal calf serum was approximately proportional to the titer of Friend spleen focus-forming virus to whcih the bone marrow cells had been exposed. This system should prove useful for investigation in vitro of Friend virus--host cell interactions which lead to erythropoietin-independent erythropoiesis.