Augmentation of in vitro human marrow erythropoiesis under physiological oxygen tensions is mediated by monocytes and T lymphocytes

Tissue and marrow (BM) in vivo O2 tensions have been estimated at 23 to 40 mm Hg (3% to 5% O2). We have investigated cellular regulation of burst-forming units-erythroid (BFU-E) under 5% O2. BFU-E from BM mononuclear cells (MNC) were cultured in methylcellulose medium and erythropoietin (Ep) +/- monocyte-conditioned medium (MoCM, a source of burst-promoting activity, BPA) in the presence or absence of autologous T cells (T) and/or monocytes (M phi) under either 5% or 21% O2 after depletion of T (MNC-T), M phi (nonadherent buoyant cells, NAB) or both T and M phi depletion (NAB-T). MNC BFU-E growth under 5% O2 was augmented over 0.1 to 1.5 U/mL of Ep. BFU-E augmentation under 5% O2 was abolished by depletion of BM M phi, T, or both from MNC. The addition of MoCM affected neither a BFU-E increase under 5% O2 nor the abrogation of that increase upon T or M phi depletion. The addition of 5% to 20% M phi or 10% to 20% T to NAB-T failed to restore the BFU-E increase under 5% O2. However, BFU-E augmentation under 5% O2 was reestablished when 10% autologous M phi, 10% T, or 10% T plus 10% M phi were added back to marrow NAB, MNC-T, or NAB-T. BM BFU-E was not augmented in the presence of varying concentrations of catalase, superoxide dismutase, or reduced glutathione at 21% O2; moreover, BFU-E augmentation was maintained at 5% O2 relative to 21% O2 in the presence of each of these antioxidants. CM prepared under 5% or 21% O2 from BM M phi, T, or M phi plus T were assessed for BPA against BM NAB-T using a sensitive BPA assay incorporating delayed Ep addition to cultures. Only CM from mixtures of M phi and T cells at 5% O2 demonstrated potent BPA; little or no BPA was detected with T or M phi CM at 5% O2 and at 21% O2 or T and M phi CM at 21% O2. The sensitivity of NAB-T BFU-E to exogenous BPA was virtually identical at 21% and 5% O2. These results indicate that human BM BFU-E are augmented under 5% O2 and that T cells and M phi together mediate that augmentation by collaborating to produce BPA-like activity in response to physiological O2 tensions.     

Mitogen-induced stimulation and suppression of erythroid burst promoting activity production by human mononuclear cells

Exposure of human peripheral blood mononuclear cells or highly enriched monocytes to various plant lectins substantially alters their production of erythroid burst promoting activity (BPA). Neither unstimulated, nor mitogen stimulated, enriched T lymphocytes produced demonstrable BPA. Each of the lectins tested resulted in a different pattern of alteration of BPA production by mononuclear cells. Increasing concentrations of phytohaemagglutinin (PHA) caused a progressive increase in BPA production up to a plateau level at concentrations above 0·25–0·5 μ1/ml. Concanavalin A (Con A) at concentrations of 0·05–0·1 μg/ml stimulated BPA production, but Con A concentrations > 1 μg/ml never augmented BPA production by mononuclear cells. Pokeweed mitogen inhibited BPA production by mononuclear cells in a concentration-dependent manner. Since PHA and Con A can bind to and stimulate both monocytes/macrophages and T lymphocytes, some production of BPA by stimulated T cells in the presence of monocytes cannot be ruled out. Earlier studies demonstrated that T cells augment monocyte production of BPA. Thus, monocyte–T cell interactions, as well as activation of monocytes and perhaps lymphocytes, play an important role in regulation of BPA production in vitro .     

Human peripheral blood erythroid burst forming unit (BFU(E)): evidence against T-lymphocyte requirement for proliferation in vitro

Erythroid burst-forming units (BFU(E)) are proliferative cells which may be precursors of the erythroid colony-forming unit (CFU(E)). To examine the role of T lymphocytes in the proliferation and/or differentiation of human blood BFU(E), the effect of purified T lymphocytes on erythroid colony (EC) formation by purified null cells was examined in vitro. Lymphocyte subpopulations were prepared by Ficoll-Hypaque centrifugation, immunoadsorbent chromatography, and sheep red blood cell rosetting after removal of monocytes by adherence to plastic. Cultures of isolated B, T, or null lymphocytes alone revealed that BFU(E) were present in the null cell fraction. Addition of isolated B and/or T lymphocytes in various ratios to null cells failed to influence the number or size of EC formed. These results indicate that normal human circulating BFU(E) are contained in the null cell fraction of peripheral blood lymphocytes and do not require T lymphocytes for normal growth and differentiation in vitro.     

Factors that affect human hemopoiesis are produced by T-cell growth factor dependent and independent cultured T-cell leukemia-lymphoma cells

Some laboratory results and clinical situations suggest that human T cells may be important in the regulation of growth of hematopoietic cells. Since the discovery of T-cell growth factor (TCGF), systems are now available for the long-term specific in vitro propagation of mature normal or neoplastic human T cells, providing an opportunity to study the influence of T cells on hematopoiesis. Recently, 24 cell lines from patients with cutaneous T-cell lymphoma (CTCL) and T-cell acute lymphoblastic leukemia (T-ALL) were grown with TCGF and then assessed for release of humoral factors that affect hematopoiesis. Conditioned media (CM) from these cell lines were tested for erythroid burst- promoting activity (BPA) and granulocyte colony-stimulating activity (CSA). BPA was detected in CM from 3/6 cultures of T-ALL patients and 4/6 CTCL cultures. CSA was found in the CM from 6/8 cultures of T-ALL patients, 7/12 CTCL cultures, and 3/4 CTCL cell lines that become independent of exogenous TCGF for growth. The CSA from several of the neoplastic T-cell cultures stimulated high levels of eosinophil colonies, a possible source of the eosinophilia seen in these patients. The ability of continuously proliferating human T lymphocytes, which retain functional specificity and responsiveness to normal humoral regulation, to produce factors that directly or indirectly stimulate myeloid and erythroid colony formation lends further credence to the role of T lymphocytes in regulating hematopoiesis.     

B-lymphocyte-derived erythroid burst-promoting activity is distinct from other known lymphokines

Previously we have demonstrated that, in contrast to various panspecific or multilineage hematopoietic growth factors, lymphocyte- derived erythroid burst-promoting activity (BPA) is lineage specific, stimulating BFU-E proliferation in serum-free culture by up to 600% of control values while failing to enhance nonerythroid colony formation. To further determine the cellular source(s) of this important erythropoietic growth regulator, we have separated normal nonadherent peripheral blood and splenic lymphocytes by nylon wool fractionation, SRBC rosetting, and panning with monoclonal antibodies (MoAbs). These unstimulated T- and B-lymphocyte-enriched populations were used as cell sources to produce conditioned media (CM) and to prepare plasma membranes (PM). When CM fractions or purified PM were assayed in serum- free human bone marrow culture, BPA was localized entirely to the B- lymphocyte-derived fractions. While CM or PM from unstimulated T lymphocytes failed to stimulate BFU-E proliferation, activation of T cells by either phytohemagglutinin-M (1%) or concanavalin A (Con A; 5 micrograms/mL) induced the expression of a factor on the PM and in the resultant CM that stimulated the formation of erythroid bursts. In addition to enhancing BFU-E proliferation, this T-cell factor stimulated the proliferation of CFU-GM and CFU-GEMM in serum-free culture. When compared biochemically (in terms of temperature stability, localization by ammonium sulfate fractionation, and sensitivity to dithiothreitol) or immunochemically (using antibodies specific for lymphocyte-derived BPA, GM-CSF, or interleukin-3 [IL-3]), as well as by lineage specificity, B- and activated T-lymphocyte- derived growth factors appeared to be distinct. The burst stimulatory activities expressed by recombinant human GM-CSF and IL-3 were immunologically distinct from that associated with octylglucoside extracts of plasma membranes from resting B lymphocytes. Our results suggest that the BFU-E-directed growth-promoting activity released from activated T lymphocytes is apparently due to GM-CSF, while both resting and mitogen-stimulated normal B lymphocytes express erythroid-specific BPA and neither GM-CSF nor IL-3.     

Low burst-promoting activity (BPA) production by cord mononuclear cells is due to functional immaturity of monocytes

Cord blood mononuclear cells produced lower burst-promoting activity (BPA) than adult peripheral blood mononuclear cells when stimulated with phytohemagglutinin (PHA). In order to examine the cellular basis of the low production of BPA by PHA-stimulated cord blood mononuclear cells in the context of the functional immaturity of T cells or monocytes, we studied BPA production by T cells or monocytes from cord blood and adult peripheral blood. Cord T cells produced as much BPA as adult T cells. Monocytes themselves did not produce significant BPA at the concentration used in this experiment (1 x 10(5)/ml). BPA production by adult T cells was significantly enhanced by the presence of autologous monocytes. BPA production by cord T cells was also enhanced by the presence of adult monocytes but not by that of cord monocytes. Cord monocytes did not enhance BPA production by adult T cells either. These results indicate that cord monocytes are primarily responsible for the low BPA production by PHA-stimulated cord mononuclear cells.     

Promotion of erythropoietic bursts in culture of human bone marrow by blood-derived mononuclear cells

Summary In this report we give evidence that the addition of different amounts of irradiated mononuclear cells (MNC) from normal blood to bone marrow cell cultures containing erythropoietin produces an increase in number and size of erythropoietic bursts proportional to the number of irradiated MNC added. There was no consistent difference in the use either of autologous or of allogeneic MNC as burst-promoting activity source in normal individuals. Plating efficiency studies demonstrated that the number of BFU-E detected had a linear relationship to the number of bone marrow cells plated when 5×10⁵ blood MNC were present as BPA source. A comparison between different preparations of human leukocyte conditioned media and 5×10⁵ irradiated MNC, demonstrated that in all experiments irradiated cells stimulated the growth of a higher number of marrow-derived BFU-E. Therefore the use of 5×10⁵ irradiated MNC from normal blood is proposed as standard BPA source in human bone marrow erythropoietic cultures.Research work supported by the Deutsche Forschungsgemeinschaft, the Commission of the European Communities (Euratom), The Federal Ministry of Interiors and the Volkswagen Foundation     

Production of erythroid burst-promoting activity (BPA) and granulocyte-monocyte colony-stimulating activity (GM-CSA) by isolated human T-lymphocyte subpopulations

T-lymphocytes and monocytes are prominent among the classes of normal human cells that have been implicated in the production of the hemopoietic growth factors granulocyte-macrophage colony-stimulating activity (GM-CSA) and erythroid burst-promoting activity (BPA). To investigate the nature of the cooperativity that occurs during the elaboration of these growth factors by activated T-lymphocytes and monocytes in vitro, and to define the subsets of T cells involved in this response, we studied the production of GM-CSA and BPA by populations of T-lymphocytes isolated by fluorescence-activated cell sorting, using the monoclonal antibodies OKT3, OKT4, and OKT8. When OKT3+, OKT4+, or OKT8+ cells were incubated for five days in liquid suspension cultures, their production of GM-CSA and BPA was undetectably low. When 5% autologous monocytes were added to the cultures, no increase in the secretion of either of these classes of growth factors was noted. In the presence of concanavalin A (Con A), measurable quantities of both GM-CSA and BPA were elaborated by all three populations of T cells in the absence of monocytes; however, when autologous monocytes were added to the Con A-stimulated T cells, the secretion of both GM-CSA and BPA was markedly enhanced. In addition, we found that supernates of unfractionated T cells incubated with Con A contained not only GM-CSA and BPA but also a potent inhibitor(s) of BPA that could be demonstrated by dilution of the media and removed by gel filtration. In contrast, no inhibitor of GM-CSA was found. By molecular sieve chromatography of the supernates, GM-CSA and BPA coeluted as a single peak. However, the two biologic activities could be separated on the basis of heat stability, since GM-CSA proved to be heat labile whereas BPA did not. Our data indicate that GM-CSA and BPA derived from human T cells are similar in their apparent molecular weights and in the pattern of their production in suspension cultures in response to lectin stimulation. The secretion of both GM-CSA and BPA by Con A-stimulated T cells is facilitated by the presence of autologous monocytes, and is not restricted to either the OKT4- or the OKT8-defined subset.     

Selective generation of erythroid burst-promoting activity by recombinant interleukin 2-stimulated human T lymphocytes and natural killer cells

Because T lymphocytes and natural killer (NK) cells produce a variety of growth factors and interleukin 2 (IL2) modulates the activity of both, we assessed the ability of IL2 to stimulate human T cells and NK cells to produce hematopoietic growth factors detectable in clonogenic marrow culture. Human recombinant interleukin 2 (rIL2) added directly to cultures of human bone marrow that had been depleted of monocytes or depleted of both monocytes and T cells caused no significant alteration of myeloid (CFU-GM) or erythroid colony formation. Conditioned media harvested from rIL2-stimulated (greater than 100 U/mL) peripheral blood mononuclear cells, T cells, Leu-2 cells, and Leu-3 cells all had erythroid burst-promoting activity (BPA) but lacked myeloid colony- stimulating factor (GM-CSF) or CFU-GM-inhibitory activity. These T cells were IL2 receptor-negative, and the addition of anti-IL2 receptor monoclonal antibody (anti-Tac) to T cell cultures did not abrogate this IL2-stimulated BPA production. In addition, Percoll gradient-enriched, large granular lymphocytes (LGL) were separated by fluorescence- activated cell sorting into Leu-11+ (NK) cells and Leu-11- (low-density Leu-4+ T) cell fractions. rIL2 stimulated LGL, Leu-11+ and Leu-11- cells to produce BPA but not detectable GM-CSF or CFU-GM-inhibitory activity. Leu-11+ (NK) cells were Tac-negative from days 0 through 14 of culture. We conclude that rIL2 at high concentrations stimulated T cells, Leu-2 and Leu-3 cell subsets, LGL, and NK cells to produce BPA but not GM-CSF and that this stimulation may be mediated by an IL2 receptor distinct from Tac or by an epitope of the IL2 receptor not recognized by the anti-Tac antibody.     

Enhancement of human erythroid progenitor cell growth by media conditioned by a human t-lymphocyte line

Recent studies have shown that soluble factors elaborated by human T lymphocytes enhance erythroid burst formation by human peripheral blood null cells. This study demonstrates that media conditioned by a long- term T lymphocyte line augmented the growth of erythroid colonies in vitro in the presence of erythropoietin (Ep). ATCC.CCl 119 (CCRF-CEM) was derived from a patient with ALL of T-lymphoblast origin. Cells from the stocks used in these experiments maintained T-cell characteristics as determined by histochemical and rosetting techniques. Increased numbers of 16 day BFU-E were seen when Ficoll-Hypaque separated peripheral blood leukocytes were cultured in the presence of a 10% (v/v) concentration of CCL 119 conditioned medium (CM). CM increased the number of BFU-E even when Ep or fetal calf serum were not growth limiting. CM also increased the number of late BFU-E observed in cultures of nonadherent bone marrow cells. When peripheral blood mononuclear cells were depleted of E-rosetting cells, only small numbers of BFU-E grew. Addition of 119 CM increased the numbers of BFU- E in E-rosette-depleted cultures. CM from B-cell, macrophage, or other T-cell lines tested did not stimulate BFU-E growth as consistently. These studies indicate that CM obtained from ATCC.CCL 119 cells contained burst-promoting activity, one of the factors required for proliferation of early erythroid progenitors.     

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

Summary. 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.     

B-lymphocytes as a source of cell surface growth-promoting factors for hematopoietic progenitors

Although B cells reside in the bone marrow, little is known concerning their functional role in hematopoiesis. We have measured the effects of surface membrane factors released from unstimulated, circulating B cells of normal donors and patients with chronic lymphocytic leukemia on human hematopoiesis in vitro. Leukemic cells augment erythroid burst formation by allogeneic blood cells (p less than 0.05). The stimulatory effect is increased in cultures containing a high B-cell seeding density, and is decreased in those with a high peripheral blood mononuclear cell seeding density. Medium conditioned by B cells (CM) from the circulation or bone marrow stimulates the formation of erythroid bursts, granulocyte-macrophage colonies, and mixed colonies containing granulocytes, erythroblasts, monocytes, and megakaryocytes (GEMM) in serum-free cultures of allogeneic and autologous marrow (p less than 0.05). This effect is localized primarily to surface membrane vesicle-rich pellets of CM. Screening of several hematopoietic and nonhematopoietic cell types reveals that membrane vesicle-associated activity is released from B cells and mitogen-stimulated, circulating T cells. In contrast, vesicles shed from freshly isolated, resting T cells, continuous T-cell leukemia cell lines, erythrocytes, and endothelial cells do not express the activity (p greater than 0.10). The stimulatory activity is augmented in cultures of marrow cells that are depleted of B4 antigen-positive lymphocytes but not of T-lymphocytes, suggesting that endogenous release of the factor(s) occurs during incubation. Furthermore, membranes partially purified from leukemic B cells also express the activity. Together with our findings that (1) the growth enhancing factor(s) is solubilized by octylglucoside, and that (2) the factor can be immunoprecipitated with BPA-neutralizing, antimembrane IgG, our results suggest that the erythropoietic activity is an integral membrane protein that may be immunologically related to BPA. The relationship of the erythroid burst stimulatory factor to other hematopoietic activities found in CM pellets is unknown.     

Early circulating erythroid progenitor cells and expression of erythropoietin receptors in sickle cell disease

Abstract: The ability of circulating progenitor cells from 22 patients with sickle cell disease (SCD) to develop erythroid colonies was studied in vitro in the presence or absence of growth factors (5637-CM and erythropoietin). In both conditions, SCD patients presented significantly higher numbers of circulating burst-forming unit-erythroid (BFU–E/5×10⁵MNC) when compared to control subjects. The study of the expression of erythropoietin receptors revealed an increased level in SCD patients. Moreover, there was a correlation between both stimulated and autocrine (without stimulus) BFU–E and the expression of erythropoietin receptors. These results are of particular interest since they indicate that the phenomenon of spontaneous BFU–E-derived colonies observed in SCD patients may be due to an increased expression of erythropoietin receptors.     

Selective apoptosis of monocytes and monocyte-derived DCs induced by bortezomib (Velcade)

Bortezomib, a proteasome inhibitor, has shown immunosuppressive activity in animal models of GVHD. In this study, we evaluated the effects of Bortezomib on the survival of monocytes, a major circulating source of DCs. PBMCs or purified CD14+ monocytes were cultured for 24 h with Bortezomib (0.1-100 ng/ml). Apoptosis was demonstrated on the basis of detection of phosphatydilserine. Bortezomib induced a significant dose-dependent depletion (P=0.008) of monocytes in PBMC preparations, with <1% CD14+ cells remaining at doses >or=5 ng/ml. Moreover, Bortezomib decreased the survival of purified monocytes within 24 h (P=0.004) (n=6). Monocyte loss was due to apoptosis (effective dose 50%, ED(50), 1-10 ng/ml). In addition, both immature and mature monocyte-derived DC underwent apoptosis following exposure to Bortezomib. Kinetic experiments showed that apoptosis increased at 16 h through 24 h of culture. However, short term (4 h) incubation with Bortezomib irreversibly committed monocytes to undergo apoptosis at 24, 72 and 144 h. Instead, Bortezomib induced no apoptosis of purified CD19+ B, CD3+ T lymphocytes and CD34+ progenitor cells (ED(50) >50 ng/ml). The inhibitory effect of Bortezomib on professional APCs, such as monocytes and DCs, suggests its possible use in GVHD prophylaxis.     

Mouse osteoblastic cells (MC3T3-E1) at different stages of differentiation have opposite effects on osteoclastic cell formation

Using our new culture system for multinucleate cells (MNCs) that have many characteristics of osteoclasts, we examined the effects of factors produced by osteoblastic cells on osteoclastic cell formation. Conditioned medium (CM) from undifferentiated osteoblastic MC3T3-E1 cells during their growth phase inhibited MNC formation in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Diluted CM (1:81) from differentiated cells obtained after cultivation for more than 20 days stimulated MNC formation, but at lower dilutions inhibited their formation. Dialyzed CM (greater than 2000 mol wt) from the differentiated cells was more stimulatory than undialyzed CM and showed no inhibitory effect on MNC formation. The inhibitory effect was observed with filtered (less than 3000 mol wt) CMs and was specific for osteoblastic cell CM. Prostaglandin E2 (PGE2) was detected in the CM from undifferentiated or differentiated MC3T3-E1 cells at concentrations (317 +/- 66 and 1287 +/- 179 pg/ml, respectively) sufficient to inhibit MNC formation, and this inhibition was partially abolished with CM (at 3-fold dilution) in indomethacin-treated cells (PGE2, less than 20 pg/ml), suggesting PGE2-mediated inhibition of MNC formation and the presence of another factor(s) besides PGE2 that influenced MNC formation. In contrast to day 3 CM plus 1,25-(OH)2D3, day 60 CM plus 1,25-(OH)2D3 induced MNC formation even in the absence of GM-CSF, and this induction was inhibited by an antibody to GM-CSF. Secondary colony formation assays showed the presence of a GM-CSF-like factor in the day 60 CM. These findings indicate that osteoblastic cells are involved in the process of osteoclastic cell formation, with at least two soluble factors produced by osteoblasts, a GM-CSF-like factor, which is stimulatory, and PGE2, which is inhibitory. The effects of CMs also differed depending on the stage of osteoblast differentiation.     

Regulation of human peripheral blood erythroid burst-forming unit growth by T lymphocytes and T lymphocyte subpopulations defined by OKT4 and OKT8 monoclonal antibodies

To reexamine the influence that T lymphocytes have on the regulation of human peripheral blood burst-forming unit (BFU-E) proliferation in the absence of a statistically significant number of monocytes, very low numbers (3 to 10 X 10(3)/mL) of a null cell fraction highly enriched for BFU-E were cultured alone and in the presence of 5 X 10(5) sheep erythrocyte-purified, autologous T lymphocytes in a methylcellulose culture system containing erythropoietin. T lymphocytes consistently enhanced the growth of BFU-E from the null cell fraction, as reflected in both their number and size. Irradiation of T lymphocytes prior to coculture with null cells markedly reduced this enhancement, strongly suggesting that T lymphocytes synthesize erythroid burst-promoting factors (BPA). To determine whether there were functional differences between the two major T lymphocyte populations as defined by OKT4 (T helper/inducer) and OKT8 (T suppressor/cytotoxic) murine monoclonal antibodies to stimulate the growth of BFU-E, both T cell subpopulations were isolated by negative (panning) or positive (fluorescence-activated cell sorting) selection and cocultured with null cells. No statistically significant differences emerged between unseparated, OKT4+ and OKT8+ T lymphocytes in their ability to stimulate the growth of BFU-E. Thus, these studies provide further evidence that T lymphocytes are a major population of BPA-producing cells and further that OKT4+ and OKT8+ T lymphocytes equally elaborate these factors.     

Induction of granulocyte and granulocyte-macrophage colony-stimulating factors from human monocytes stimulated by Fc fragments of human IgG

The effect of human IgG on human haemopoiesis has been studied in vitro. Dialysed purified IgG stimulated haemopoietic colony growth by bone marrow mononuclear cells (MNC) but not by monocyte-depleted MNC. Culture media, conditioned by IgG-stimulated peripheral blood MNC, augmented formation of neutrophil-macrophage, eosinophil, and megakaryocyte colonies by monocyte-depleted marrow MNC. Serum-free IgG-conditioned media also contained colony-stimulating activity (CSA). IgG Fc fragments and heat-aggregated IgG promoted the secretion of CSA, but F(ab')2 fragments, Fab fragments or ultracentrifuged IgG did not. In the cell-selection studies, CSA was produced by highly enriched monocytes following stimulation with Fc fragments. The antiserum against human granulocyte colony-stimulating factor (G-CSF) and/or granulocyte-macrophage CSF (GM-CSF) neutralized the CSA produced by Fc fragment-activated monocytes. Enzyme immunoassays showed G-CSF and GM-CSF in media conditioned by monocytes stimulated with the Fc fragments, heat-aggregated IgG and anti-D-sensitized red blood cells (RBC). Northern hybridization analysis showed mRNA encoding G-CSF and GM-CSF in RNA extracted from MNC and monocytes cultured with the Fc fragments, but not in the RNA from unstimulated cells or monocyte-depleted MNC. These results indicate that IgG Fc fragments, aggregated IgG and antigen-antibody complexes induce monocytes to produce G-CSF and GM-CSF in vitro. The CSFs release induced by IgG may be involved in the in vivo regulatory network in haemopoiesis.     

Inadequate ability of T-lymphocytes from chronic uremic subjects to stimulate the in vitro growth of committed erythroid progenitors (BFU-E)

The growth of normal burst-forming units (BFU-E) is known to depend on a burst-promoting activity (BPA) produced by T-lymphocytes. Few BFU-E colonies have been observed in cultures of blood mononuclear cells (MNC) of uremic patients. The aim of the present study was to examine the concentration of BFU-E in the blood of uremic patients and to evaluate the ability of uremic T-lymphocytes to produce BPA. We have studied 6 chronic uremic patients treated with maintenance hemodialysis. When 5 X 10(5) blood MNC depleted of T-lymphocytes of uremic subjects were stimulated by 1 X 10(6) normal T-lymphocytes in a methylcellulose culture system we observed the growth of a number of BFU-E colonies that did not differ significantly from normal (29 +/- 11.8 colonies). On the contrary, when 5 X 10(5) blood MNC depleted of T-lymphocytes of normal subjects were stimulated by 1 X 10(6) T-lymphocytes of uremic patients, the number of BFU-E colonies obtained was significantly lower than normal (1.9 +/- 3.1 colonies). These data show that the decreased number of BFU-E colonies obtained from blood MNC of uremic patients is due to a defect of uremic T-lymphocytes. The impairment of T-lymphocytes can be due to inhibitors of T-lymphocyte function or to variations in T cell subsets, leading to a decrease in the OKT4/OKT8 cell ratio. In any case it is a significant pathogenetic mechanism contributing to anemia in chronic uremia.     

Monocytes in rheumatoid arthritis. Regulatory, effector, and phenotypic properties

We reported that rheumatoid arthritis (RA) blood mononuclear cells (MNC) secreted less Ig and IgM rheumatoid factor (RF) than synovial cells. Since antibody elaboration is partly monocyte dependent, we compared regulatory, effector, and phenotypic properties of monocytes from 31 patients with RA with those of 21 normal subjects. RA IgG and IgM elaboration was less than normal. Monocyte, T or B cell numbers were comparable in RA and normal MNC and monocyte enriched/depleted preparations. RA and normal Ig production were monocyte dependent and this differed for IgG and IgM for RA and normals. IgM RF elaboration by stimulated RA MNC was also monocyte dependent and addition of normal monocytes/monocyte culture supernatants to RA monocyte depleted cultures and vice versa had inconsistent effects. RA MNC (Ficoll-Hypaque) phagocytosis was less than normal; killing (acridine orange fluorescent microscopy) was not. RA synovial monocyte phagocytosis - but not killing was also reduced. MNC from RA patients and normals contained similar numbers of monocytes; RA monocyte enriched populations (Percoll) showed less phagocytosis than normal; with similar killing. RA phagocytosis was reduced at 1,2,3,4 and 5 h and differed from normal at 3 and 5 h. Different sera - FCS, autologous, normal, RA - exhibited inconsistent effects on phagocytosis. RA and normal neutrophil phagocytosis and killing were comparable. Lastly, RA monocyte enriched preparations contained populations of OKM1, OKM3, OKM5, OKM6, Leu M1, Leu M2, Leu M3, and HLA-DR-positive cells (FACS analysis) comparable with normals. Regulatory and effector but not phenotypic properties of RA blood monocytes differed from normal and may contribute to inappropriate autoantibody production and chronic inflammation.     

Mechanism of the damaging effect of dermatomyositis mononuclear cells on cultured human skin fibroblasts

We further studied the mechanism of action of peripheral mononuclear cells (MNC) from patients with dermatomyositis (DM) to strikingly suppress fibroblast proliferation in vitro. Attachment of MNC to fibroblasts was closely related to the mechanism. Most of attached MNC were activated T lymphocytes. Conditioned medium alone did not show any effects on fibroblasts. T8 positive cells and monocytes were essential to elicit the effect. Study of 51Cr release demonstrated that DM MNC augmented cytolysis of fibroblasts. It might be concluded that DM MNC possess T lymphocyte mediated cytotoxicity on fibroblasts and this causes the inhibition of fibroblast proliferation.