Monocytes do not inhibit peripheral blood erythroid burst forming unit colony formation

Inhomogeneity of the circulating BFU-E regulation in sickle cell anaemia: accessory cells properties and BFU-E growth factor response pattern

Sickle cell anaemia (SS) patients with low (< 9%) HbF levels (LFSS) are characterized by an increased number of circulating BFU-E in active DNA synthesis, and release of burst promoting activity (BPA) by unstimulated low density (LD) adherent cells. In contrast, circulating BFU-E from SS patients with high (> 9%) HbF levels (HFSS) are normal in number, largely in resting phase, and their LD cells do not release BPA-like activity. We report now that in LFSS patients, adherent cell depletion decreases BFU-E growth in culture and apparent BFU-E cycling. Furthermore, addition of conditioned media (CM) from LD cells of LFSS patients restored cycling BFU-E expression in culture. Neutralization analysis with anti-GM-CSF antibody demonstrated that GM-CSF is, at least, one factor responsible for BPA activity present in this CM. Thus, GM-CSF is constitutively produced by unstimulated monocytes in LFSS patients. In contrast, HFSS patients' adherent cell depletion increases cycling of BFU-E in culture. CM from HFSS patients inhibits BFU-E expression in culture. Hence, LD adherent cells from HFSS patients may release a yet unknown inhibitor factor(s). In addition, we report a distinct response pattern in SS patients' BFU-E to growth factor (GM-CSF, IL-3): (a) LFSS patients have a BFU-E population, equally responsive to GM-CSF and IL-3; (b) HFSS patients, have a subset of BFU-E exclusively dependent on IL-3 (20-40% of the circulating BFU-E). This pattern is very similar to that of normal BFU-E. In conclusion, BFU-E from LFSS patients represent an actively proliferating population, equally responsive to GM-CSF and IL-3, controlled by constitutively produced GM-CSF, suggesting a unique BFU-E behaviour in SS patients with low HbF levels and high haemopoietic stress. The heterogeneous regulation of BFU-E in SS disease seems to be the epiphenomenon of HbF levels, and not vice versa.

Early circulating erythroid progenitors (BFU-E) in sickle cell anemia

Sickle cell anemia (SS) patients can be divided into two sub-populations according to peripheral HbF levels. Patients with low (< 9%) HbF levels (LFSS) are characterized by an increased number of circulating BFU-E in active DNA synthesis, and release of burst promoting activity (BPA) by unstimulated low density (LD) adherent cells. In contrast, circulating BFU-E from SS patients with high (> 9%) HbF levels (HFSS) are normal in number, largely in resting phase, and their LD cells do not release BPA-like activity. More recently further heterogeneity has been found among these two groups. In LFSS patients GM-CSF is constitutively produced by unstimulated monocytes. In contrast, HFSS patients' adherent cell depletion increases cycling of BFU-E in culture. CM from HFSS patients inhibits BFU-E expression in culture. Hence, LD adherent cells from HFSS patients may release an inhibitory factor(s). The nature of this factor has to be determined. In addition, there are distinct subpopulations of BFU-E responsiveness to growth factor (GM-CSF, IL-3): a) LFSS patients have a homogeneous BFU-E population, equally responsive to GM-CSF and IL-3; b) HFSS patients, in addition to this subpopulation, have a subset of BFU-E dependent exclusively on IL-3 which is 20 to 40% of the total number of circulating BFU-E. This is similar to BFU-E from normal individuals. Hence, LFSS BFU-E represent an actively proliferating population, equally responsive to GM-CSF and IL-3, controlled by at least constitutively produced GM-CSF and possibly other factors. These observations suggest a significant modification in BFU-E behavior in the subset of SS patients with low HbF levels and high hemopoietic stress. The heterogenous regulation of BFU-E in SS disease seems to be an epiphenomenon of HbF levels, and not vice-versa.

Regulation of hematopoiesis by T lymphocytes and natural killer cells

T lymphocytes and natural killer (NK) cells exert both stimulatory and suppressive effects that regulate growth and differentiation of hematopoietic cells. Activated T and NK cells have been demonstrated in different pathological states of bone marrow failure and are proposed to play a role in the pathogenesis of the disease. T and NK cells have also been shown to be responsible for bone marrow graft rejection in both allogeneic and syngeneic donor/recipient combinations. Lymphocytes can regulate hematopoietic cell growth by direct cellular contact or by releasing soluble factors, such as colony-stimulating factors, immune interferon, lymphotoxin, and tumor necrosis factor, active on hematopoietic precursor cells.

T cells and erythroid burst forming units in chronic lymphocytic leukemia

Substantial evidence exists indicating T cell abnormalities in chronic lymphocytic leukemia (CLL). There is also evidence that the T cell is an important source of burst promoting activity (BPA) for the peripheral blood (PB) erythroid burst forming unit (BFU-e). We studied the BPA of T cells and response of BFU-e in normals and untreated early stage B cell CLL patients in a methylcellulose colony assay. Normal null cell cultures grew significantly more BFU-e than CLL null cell cultures. Addition of autologous T cells to normal or CLL null cells significantly increased BFU-e only in normals. Allogeneic coculture of T cells from CLL patients with null cells from normals yielded normal responses of BFU-e in five of six cases. In contrast, allogeneic coculture of normal T cells with CLL null cells yielded a normal response in only one of six studies. Furthermore, adding increasing quantities of autologous or normal allogeneic T cells to CLL null cells did not augment the BFU-e response. Accounting for the expanded lymphocyte pool in CLL, BFU-e are decreased in concentration but the absolute number is normal or increased. The decrease in concentration could be secondary to expansion of the null cell fraction in CLL by pre-B cells. CLL T cells appeared to augment normal allogeneic PB BFU-e in a normal fashion, whereas, in several cases, CLL BFU-e were hyporesponsive to autologous or normal allogeneic T cells. It is therefore apparent that in untreated early stage B cell CLL, erythroid progenitor cells are present in the peripheral blood but are diluted in an expanded null cell compartment and may, in some cases, be hyporesponsive to T cell BPA. T cell BPA of CLL T cells in this early stage of disease is preserved.

Susceptibility to merocyanine 540-mediated photosensitization: a differentiation marker on murine hematopoietic progenitor cells

Merocyanine 540 (MC 540) is an impermeant fluorescent dye that binds preferentially to fluidlike domains of the cell membrane. Photoexcitation of membrane-bound dye causes a breakdown of the normal permeability properties of the membrane and, eventually, cell death. We have used in vitro and in vivo clonal assays to determine the relative sensitivities of different classes of normal murine hematopoietic progenitor cells to MC 540-mediated photosensitization. Late erythroid progenitors (CFU-E) were the most sensitive cells, followed in order of decreasing sensitivity by early erythroid progenitors (BFU-E), megakaryocyte progenitors (CFU-Meg), day 7-spleen colony forming cells (day 7-CFU-S), granulocyte/macrophage progenitors (CFU-GM), and day 11-spleen colony forming cells (day 11-CFU-S). Bipotent progenitors of the granulocyte/macrophage lineage were more sensitive than unipotent macrophage progenitors but less sensitive than unipotent granulocyte progenitors. Progenitors giving rise to large granulocyte/macrophage colonies were more sensitive than progenitors giving rise to small colonies ("clusters"). We conclude that sensitivity to MC 540-mediated photosensitization is develop-mentally regulated and that differences occur even between the most closely related classes of progenitor cells. Our findings indicate the usefulness of MC 540 as a plasma membrane probe. They also support the contention that early and late-appearing spleen colonies are the progeny of two distinct classes of progenitor cells.

Fetal hemoglobin accumulation in vitro. Effect of adherent mononuclear cells

In clonal cultures of erythroid burst-forming units (BFU-E) obtained from blood, the accumulation of fetal and adult hemoglobins (Hb F and Hb A) was measured by radioligand immunoassay. Inclusion of adherent mononuclear cells in the culture promoted a striking increase in the relative amount of Hb F in each of 44 experiments with 14 donors. In two-thirds of the instances, this was accounted for by a selective increase in the absolute amount of Hb F. The differential effect on Hb F and Hb A accumulation was achieved without altering the maturity of the erythroid cells, their mean hemoglobin content, or the asynchrony of the production of the two hemoglobins. Virtually all bursts produced Hb F, and the population of BFU-E as a whole, rather than a selected subset, appeared to be the target of adherent cell action. When the adherent cells were excluded from the culture input, the base-line value of Hb F was reproducible for each donor over a period of several months, and correlated with the number of in vivo circulating F cells.

Anemia associated with rheumatoid disease. Inverse correlation between erythropoiesis and both IgM and rheumatoid factor levels

Cell culture techniques were used to evaluate the number of erythroid colonies formed by circulating progenitor cells from 24 patients with rheumatoid disease and controls. A highly significant inverse correlation was demonstrated between erythroid colony counts and serum IgM and rheumatoid factor concentrations in the rheumatoid patients. The potential role of these factors in the pathogenesis of the anemia of rheumatoid disease is discussed.

Effect of blood derived monocytes on the promotion of in vitro erythropoietic colony growth in human bone marrow cultures

The effect of monocytes on the promotion of erythropoietic burst formation in human bone marrow methylcellulose cultures was studied in a burst-promoting activity (BPA)-poor system. Irradiated Ficoll-Isopaque separated blood mononuclear cells stimulated BFU-E growth proportionally to the number of irradiated cells added. Monocyte-depleted mononuclear cells stimulated as well as total mononuclear cells. Monocyte-concentrates stimulated when added at low concentrations. Monocyte-depleted mononuclear cells, although stimulatory at higher concentrations, did not stimulate at the concentrations used for monocyte-concentrates.

In vitro suppression of erythropoiesis by bone marrow adherent cells from some patients with fungal infection

We present evidence that alterations in marrow adherent cell (M phi) function may play a role in the suppression of erythropoiesis in some patients with fungal infection. Bone marrow (BM) cells from 12 normals and 10 patients with histoplasmosis were cultured in plasma clots before and after removal of M phi. BM from five patients (Group A) produced normal numbers of erythroid colonies (EC). In the remaining patients (Group B), smaller numbers of EC were detected (P less than 0.01). Removal of M phi from BM of normals and Group A patients resulted in decreased growth of EC. In contrast, M phi depletion of BM from patients in Group B resulted in greater EC formation (P less than 0.01). When normal M phi were admixed with normal or patients' BM-M phi, enhanced EC formation resulted. Whereas, at similar concentrations, M phi from group B patients caused inhibition of EC formation (P less than 0.005). The erythro-regulatory function of M phi, including the inhibitory action of patients' M phi, was mediated via a soluble agent(s) since media conditioned by M phi mimicked the action of these cells. Three patients in Group B were restudied 14 months after treatment with amphotericin B, when blood parameters had returned to normal. At this time, normal patterns of EC formation and M phi activity were observed.

Hb switching in neonatal cultures. Increase of Hb A synthesis in presence of an erythroid potentiating activity (EPA)

The role of EPA (erythroid potentiating activity) on the growth and on the pattern of hemoglobin synthesis in erythroid colonies from human neonates was investigated. Conditioned medium from the Mo cell line was used as a source of EPA. The results have shown that the addition of Mo medium to cultures determined a significant enhancement of the number and size of BFU-E and an increase of beta chain synthesis. The acceleration of hemoglobin switching is not related to an amelioration of the maturation of the erythroid colonies when grown in the presence of Mo medium. The enhancement of Hb A synthesis induced by Mo medium can directly be related to its EPA, which may operate by two different mechanisms: (1) the recruitment of early erythroid progenitors already preprogrammed to synthesize prevalently beta chains, or (2) the modulation of beta and gamma gene activity in cord blood BFU-E. Some evidence suggests that the first mechanism does operate.

Erythroid colony growth in vitro from human peripheral blood null cells: evidence for regulation by T-lymphocytes and monocytes

Colony assays in methylcellulose of primitive erythroid precursors (BFU-E) were carried out from the null cell fraction of normal human peripheral blood lymphoid cells. There was little proliferation or maturation of BFU-E as assessed by both the number and the size of colonies formed, when null cells alone were cultured. Culture of null cells with up to 8 X 10(5) autologous T-lymphocytes per ml led to considerable stimulation of colony growth and maturation. Culture of null cells with peripheral blood monocytes also resulted in the indication of BFU-E growth, although the response was inferior to the seen with T-cells. Co-culture of null cells together with both T-cells and monocytes resulted in a uniformly greater response than with either alone, and this was shown to be due to a positive interaction between these two cell types.

Human erythroid burst-forming units. Growth in vitro is dependent on monocytes, but not T lymphocytes

The roles of monocytes and T lymphocytes in the regulation of human peripheral blood erythroid burst-forming units (BFU-E) were studied in erythropoietin-containing plasma clot cultures of subpopulations of human blood mononuclear cells. BFU-E growth was decreased significantly after depletion of monocytes alone (mean 11% of expected, range 0 to 42% of expected) or depletion of both monocytes and T cells (mean 6.5% of expected, range 0.5 to 12% of expected) from mononuclear cells. T cell depletion did not impair BFU-E growth in vitro. Using 10(5) monocyte- and T lymphocyte-depleted mononuclear cells as target cells (less than 1% monocytes, less than 5% T cells), BFU-E growth was restored to 40% of expected by addition of 10(4) monocytes, and to 96% of expected by 10(5) monocytes alone. Addition of as many as 2 X 10(5) T cells but no monocytes resulted in stimulation to only 34% of expected BFU-E growth. Addition of 2 X 10(4) T cells, which alone did not affect BFU-E growth, could augment significantly the stimulatory effect of 5-20 X 10(3) monocytes on BFU-E growth. Thus, monocytes alone appear to be capable of stimulating BFU-E growth in vitro in the presence of erythropoietin. T cells also may make small quantities of BFU-E stimulators. However, it seems more likely that the most important role of T lymphocytes in BFU-E regulation in vitro is a result of interactions with monocytes and augmentation of monocyte production of stimulators of BFU-E growth.

Monoclonal antibody assessments of T cell interactions in erythropoietin studies

The contemporary application of clonal assay techniques has greatly expanded our knowledge of the regulation of hematopoiesis. Our efforts have been directed toward the investigation of non-erythropoietin-mediated regulation of human erythropoiesis in the form of cell-to-cell interaction between mature T cells and erythroid progenitors. Our data indicate that three such progenitors, the early marrow erythrocyte precursor BFU-E, the more mature marrow erythrocyte precursor, CFU-E and the peripheral blood BFU-E, each exhibit totally different requirements for their colony expression in culture, with respect to the absence of erythropoietin and the presence of mature T cells or their products. The capacity of erythroid progenitors to withstand incubation in the absence of erythropoietin appears to be a characteristic of immature rather than mature erythroid progenitors. Furthermore, use of OKT3 antibody depletion techniques shows that peripheral blood-derived BFU-E appear to depend upon mature lymphocytes or T cell-conditioned medium for erythropoietin-stimulated differentiation while bone marrow BFU-E and CFU-E have no requirement for mature T cells to produce erythropoietin-dependent maturation. Our results, plus a vast array of data provided by other investigators in the field, are integrated into a proposed framework for further investigation of T cell induction of erythropoietin-dependent erythroid differentiation aimed at more specifically identifying the inducer cell subset(s) in that system.