Regulation of colony-stimulating activity production. Interactions of fibroblasts, mononuclear phagocytes, and lactoferrin

Characterization of the in vitro stromal microenvironment of human bone marrow

Utilizing long-term in vitro culture techniques, we characterized the cellular composition and functional attributes of the human in vitro bone marrow stromal microenvironment. Morphologic, specific cytochemical and immunologic methods demonstrated that the marrow stromal adherent layer (AL) reached confluency at two to three weeks, and was comprised of 60%-70% fibroblastic cells, 10%-20% endothelial cells, 10%-20% monocyte/macrophages and 5%-10% fat-laden adherent cells. These proportions of cell types persisted for at least three months concomitant with proliferation of CFU-gm and BFU-e. In contrast, umbilical cord blood cells did not form a stromal AL despite persistence of hemopoietic progenitor cell proliferation. These findings provide a basis for improved understanding of cellular interactions regulating hemopoiesis.

Interleukin 1 stimulates fibroblasts to produce granulocyte-macrophage colony-stimulating activity and prostaglandin E2

Granulocyte-macrophage colony-stimulating activity (GM-CSA) can be produced by a variety of normal cell types including mononuclear phagocytes, activated T lymphocytes, endothelial cells, and fibroblasts. Recent evidence shows that a major role of the monocyte-macrophage is the recruitment of environmental cells, i.e., fibroblasts, to produce GM-CSA. In this study we have identified interleukin 1 (IL-1) as a monokine that stimulates fibroblasts to produce and release GM-CSA and prostaglandin E2 (PGE2). Both purified human monocyte-derived IL-1 and human recombinant IL-1 (10(-10) M) can be substituted for monocyte-conditioned medium in stimulating fibroblast GM-CSA and PGE2 production. Both forms of IL-1 stimulate fibroblasts to produce GM-CSA and PGE2 in a dose-dependent fashion. The fibroblast-stimulating activity found in monocyte-conditioned medium was completely blocked by anti-IL-1. We conclude that monocytes produce IL-1, and that monocyte-derived IL-1 induces fibroblasts to produce GM-CSA and PGE2.

Multilineage, non-species specific hematopoietic growth factor(s) elaborated by a feline fibroblast cell line: enhancement by virus infection

In studies designed to determine the role of feline leukemia virus (FeLV) in the pathogenesis of marrow failure in the cat, we tested medium conditioned by uninfected and FeLV-infected feline embryonic fibroblasts (FEA) for its effect on hematopoietic colony growth in culture. As opposed to an inhibitory effect, we found that the conditioned medium (CM) from FEA or FEA/FeLV increased the in vitro growth of multiple hematopoietic progenitor cell types including erythroid burst-forming cells (BFU-E), granulocyte/macrophage colony-forming cells, megakaryocytic colony-forming cells, and mixed-cell colony-forming cells. Furthermore, CM enhanced the growth of progenitors in cultures of mouse or human marrow cells, as well as cat marrow cells. Stimulation of feline BFU-E was most marked with an increment in growth of 400% over control. The human burst promoting activity (BPA) of the CM was equivalent or better than other CM available in our laboratory. The evidence suggest that the growth-promoting activity is a constitutive product(s) released by FEA which was enhanced eightfold with virus infection. Studies with non-adherent and T-lymphocyte-depleted human marrow cells and human peripheral blood cells suggest that the growth factor(s) acts directly on progenitor cells and not through readily identified accessory cells. These findings are consistent with the concept that mesenchymal cells such as fibroblasts have the capacity to release hematopoietic growth factor(s) capable of acting on primitive hematopoietic progenitors. The results provide an example of how injury of such cells, through virus infection, may enhance growth factor(s) release and influence the hematopoietic microenvironment.

Regulation of C-myc expression during growth and differentiation of normal and leukemic human myeloid progenitor cells

C-myc proto-oncogene transcripts from serially harvested, colony-stimulating activity (CSA)-stimulated, normal progenitor-enriched human bone marrow cells were compared to those of the promyelocytic leukemia cell line HL-60 and to those of freshly obtained human myeloid leukemic cells. During the early culture period both normal and leukemic cells expressed the c-myc oncogene. In normal cells maximal expression occurred after 24 h of culture and did not occur in the absence of CSA. At this time, progranulocytes predominated in the cultured cells. Although cellular proliferation occurred for 96 h in vitro, c-myc expression ceased after 24-36 h. Terminally differentiated cells predominated in these cultures by 120 h. In contrast, although leukemic cells also expressed c-myc in vitro, transcription persisted throughout the culture period and, in the case of HL-60 cells, occurred in the absence of exogenous CSA. We also noted that normal cells with only one diploid gene copy exhibited, after 24 h of culture, only twofold fewer transcripts than did HL-60 cells in which there were 16 myc copies. Furthermore, c-myc mRNA degradation rates were similar in normal cells and in HL-60 cells. We conclude that c-myc transcription is a normal event in granulopoiesis linked to proliferative activity as well as to primitive developmental stage. Furthermore, the most consistent abnormality in leukemic cells in vitro is their failure to suppress transcriptional activity of this gene. We suggest that c-myc transcription in HL-60 cells may be appropriate for cells arrested at that developmental stage and that the amplified genes in HL-60 cells are quiescent relative to c-myc in normal cells at the same differentiation stage. The techniques described herein may be of value in identifying mechanisms by which normal hematopoietic cells suppress c-myc expression and aberrancies of these mechanisms in leukemic cells.

Membrane antigen expression during hemopoietic differentiation

The pattern of certain groups of antigens expressed on the surface of hemopoietic cells changes either during the course of differentiation from pluripotent stem cells to mature functional cells or as a function of the proliferative state of the cells. A map of these changes is emerging and is providing valuable information for selecting and purifying rare stem cells and for classifying the acute leukemias. This knowledge is also beginning to provide insights into physiological and pathological cellular interactions affecting the early stages of hemopoiesis, and is being exploited to remove T lymphocytes from allogeneic bone marrow grafts in order to prevent graft-vs.-host disease as well as leukemic cells from bone marrow before autologous reinfusion. In this article I will briefly review the cellular basis of hemopoiesis and then discuss the methods used to determine the presence of antigens on normal hemopoietic cells. I will then summarize the pattern of membrane antigens expressed during differentiation and conclude by discussing the biological and therapeutic implications.

Lactoferrin: its role as a regulator of human granulopoiesis?

Lactoferrin has been proposed recently as a physiological regulator of the granulocyte-monocyte progenitor (CFU-GM). This glycoprotein, when saturated with iron, has been said to limit the CFU-GM growth by decreasing production and release of colony stimulating activity by monocytes and macrophages. Human milk lactoferrin saturated with iron, at concentrations ranging from 10(-8) M, was added either to endogenously stimulated bone marrow cells or to mononucleated cells used as feeder layers for adherent cell-depleted marrow. Irrespective of the concentration of lactoferrin within the culture system used, no significant inhibition of the CFU-GM growth was observed. Moreover, the CFU-GM stimulating activity of medium conditioned by a 4 day incubation of 1 X 10(6) mononucleated blood cells in the presence or in the absence of lactoferrin was the same. Various possible explanations for not confirming the reported inhibiting activity of iron-saturated lactoferrin were explored: (a) masking inhibition of the system by prostaglandin E2 (PGE2), (b) masking inhibition of the system by bovine lactoferrin present in the fetal calf serum, (c) preinhibition of the system by leukemic-associated inhibitory activity possibly present in the culture system, (d) the iron and calcium content of the culture medium used, (e) the fixation of lactoferrin to plastic compounds, (f) the source of the human lactoferrin used, and (g) the marrow cell separation methods used. None of these factors was shown to play a role in vitro in the activity of lactoferrin and thus no evidence was found for a significant role of lactoferrin in the regulation of human granulopoiesis.

Viral infection of vascular endothelial cells alters production of colony-stimulating activity

Viral infections in humans are frequently associated with granulocytopenia and/or granulocytosis. Such changes in myelopoiesis could result from infection of the granulocyte-macrophage colony-forming cell (CFC-GM) or changes in the production of colony-stimulating activity (CSA). Endothelial cells are a known source of CSA and may be transiently or persistently infected during a number of viral infections, including infection with herpes simplex virus type I (HSV-I) and measles virus. Therefore, we examined the effect of endothelial cell infection with these two viruses on the production of CSA. Uninfected passaged endothelial cells produce CSA when stimulated by the continual presence of a factor present in medium conditioned by peripheral blood monocytes (MCM). Within 4 h of infection with HSV-I, endothelial cells no longer produced CSA in response to MCM. In contrast, measles virus infection induced CSA production by passaged endothelial cells even in the absence of MCM. Measles virus-induced CSA production was maximal at 24 h and required the presence of live virus within the endothelial cells. The effects of HSV-I and measles virus on CSA production were not dependent on alterations in the production of alpha- or gamma-interferon by the infected endothelial cells. Infection with HSV-I did not stimulate endothelial cells to release any detectable interferon. In contrast, the supernatants of the measles-infected cells contained only beta-interferon, a known inhibitor of CFC-GM development. These studies suggest that CSA production by endothelial cells is directly altered by infection with HSV-I and measles virus. An alteration in CSA production might contribute to changes in myelopoiesis that frequently accompany viral infection in humans.

Normal human marrow stromal cells induce clonal growth of human malignant T-lymphoblasts

The effect of marrow stromal cells (MSC) on the clonal growth of a human malignant T-lymphoblast (MTL) cell line was investigated in a bilayer culture system. The MSC consistently stimulated clonal growth of MTL, and no stimulatory humoral factor was present in the medium conditioned by the MSC. These observations and other reports suggest that marrow stromal cells may provide a microenvironment in vivo that is not only conducive to the growth of malignant lymphoblasts, but may actually enhance proliferation of malignant T-lymphoblasts in the bone marrow.

Lactoferrin in the myeloproliferative disorders: a search for granulopoietic regulator defects

Evidence of a defect in the negative feedback control of granulopoiesis in the myeloproliferative disorders is presented. Neutrophil release of lactoferrin, plasma lactoferrin concentration, the number of lactoferrin receptor sites on mononuclear cells and granulocyte-monocyte colony stimulating factor (GM-CSF) release from peripheral blood cells were determined in patients with myeloproliferative disorders and compared with normal individuals. There was a significantly (P less than 0.001) decreased release of lactoferrin from the neutrophils of patients with myeloproliferative disorders which could be responsible for a reduced suppression of GM-CSF release from mononuclear cells which in turn may be responsible for the increased myeloid proliferative activity in patients with myeloproliferative disorders.

A monokine stimulates production of human erythroid burst-promoting activity by endothelial cells in vitro

Conditioned media were prepared from human peripheral blood monocytes and human umbilical vein endothelial cells. These media were assayed for erythroid burst-promoting activity (BPA) using human peripheral blood monocyte-depleted mononuclear cells as targets and assessing the stimulatory effect of the conditioned media on growth of early erythroid progenitor cells. Both monocytes and endothelial cells produced modest amounts of detectable BPA. Addition of varying concentrations of media conditioned by monocytes to plateau concentrations (5-10%) of media conditioned by endothelial cells had no additive effect. Endothelial cells incubated in the presence of 50% monocyte-conditioned medium produced 2.5- to 6.6-fold more BPA than did endothelial cells incubated only in control tissue culture medium. In contrast, endothelial cell conditioned medium did not stimulate increased BPA production by monocytes. Neither neutrophil- nor marrow fibroblastoid cell-conditioned medium stimulated BPA production by endothelial cells. Therefore, both monocytes and endothelial cells produce BPA. Moreover, monocytes produce a monokine that, in turn, stimulates the production of BPA by endothelial cells. Inasmuch as a monokine also has been shown to stimulate production of granulocyte-macrophage colony-stimulating activity, we propose that monocytes play a critical role in regulating the production of humoral regulators of the very early stages of hemopoietic cell differentiation.

Current considerations of the etiology of aplastic anemia

Aplastic anemia is a disorder characterized by marrow aplasia and pancytopenia. The pathogenetic mechanisms that lead to bone marrow aplasia have been intensively studied. Data obtained from these studies suggest that aplastic anemia is a heterogeneous disorder with regards to pathogenesis. Bone marrow aplasia may result from a number of abnormalities including qualitative or quantitative abnormalities of hematopoietic stem cells, abnormal interaction between bone marrow accessory cells (lymphocytes and macrophages) and hematopoietic stem cells, cytotoxic humoral inhibitors of hematopoiesis, and abnormalities of the bone marrow microenvironment. A number of new therapeutic options have improved the survival of patients with aplastic anemia. Allogeneic bone marrow transplantation has actually resulted in the cure of patients. Unfortunately, only a minority of patients have a suitable bone marrow donor and alternate modes of therapy have been sought. Encouraging results have been reported from several centers concerning the use of antilymphocyte serum in patients with aplastic anemia. Certainty of the ultimate long-term benefit of this type of immunosuppressive therapy is not possible until careful, randomized, prospective studies of its use are completed.

Pathology-important advances in clinical medicine: assessing fetal lung maturity

The Scientific Board of the California Medical Association presents the following inventory of items of progress in pathology. Each item, in the judgment of a panel of knowledgeable physicians, has recently become reasonably firmly established, both as to scientific fact and important clinical significance. The items are presented in simple epitome and an authoritative reference, both to the item itself and to the subject as a whole, is generally given for those who may be unfamiliar with a particular item. The purpose is to assist busy practitioners, students, research workers or scholars to stay abreast of these items of progress in pathology that have recently achieved a substantial degree of authoritative acceptance, whether in their own field of special interest or another.The items of progress listed below were selected by the Advisory Panel to the Section on Pathology of the California Medical Association and the summaries were prepared under its direction.