Human Placental Conditioned Medium Research Articles

In Vitro Cell Growth Stimulated by Recombinant Human Cytokines Can Help to Diagnose Transient Leukemia in Neonates

In a previous study, we demonstrated that in vitro cell growth stimulated by human placental conditioned medium distinguished between transient leukemia (TL) and congenital acute myeloid leukemia (AML) in neonates. We then sought to determine whether the application can be expanded if in vitro cell growths are stimulated by recombinant human cytokines including granulocyte-macrophage colony-stimulating factor (rhGM-CSF), interleukin-3 (rhIL-3), stem cell factor (rhSCF) and thrombopoietin (rhTPO). Eight neonates with features indistinguishable from AML were studied. Seven patients had Down syndrome and the eighth a normal phenotype. Bone marrow or peripheral blood mononuclear cells (MNC) were cultured in the presence of rhGM-CSF+rhIL-3+rhSCF or of rhTPO alone. After incubation, granulocyte-macrophage colony-forming units (CFU-GM)-derived colonies and clusters were scored on an inverted microscope. Colony-forming units-megakaryocyte (CFU-MK)-derived colonies were counted with an in situ CD61 immunostained dish. Liquid suspension cultures of MNC were stimulated by rhGM-CSF and/or rhTPO. CFU-GM-derived colonies and clusters from bone marrow and peripheral blood MNC revealed normal patterns in seven patients. RhTPO-stimulated megakaryocyte colony formation was normal in one patient. Cytospin smears of liquid suspension cultures all showed good myeloid or megakaryocytic maturation consistent with TL rather than AML. One neonate died on the 2nd day of life, but in the seven remaining patients, blasts disappeared from the peripheral blood within 10 months. Among four patients followed long-term, one developed myelodysplastic syndrome at 21 months. This child was given tailored chemotherapy and had a disease-free survival>20 months. In vitro cell growth stimulated by recombinant human cytokines can help to diagnose TL in neonates.

Granulocyte-Macrophage Colony-Forming-Unit Assay and Liquid Suspension Culture of Bone Marrow and Peripheral Blood in Newly Diagnosed Childhood Acute Lymphoblastic Leukemia

Granulocyte-macrophage colony-forming-unit (CFU-GM)-assays and/or liquid suspension cultures of bone marrow (BM) and peripheral blood (PB), using human placental conditioned medium as a source of colony-stimulating activity, were performed in 125 children with newly diagnosed acute lymphoblastic leukemia (ALL). Unlike the previous small series which invariably showed poor BM granulocyte-macrophage colony and cluster formations, we found 3 growth patterns. A poor-growth pattern was seen in 101 patients. A low-growth pattern with BM colony and cluster formations in the lower range of the normal limits was observed in 6 patients. All 6 patients had low-risk ALL, and the in vitro growth may reflect the residual normal CFU-GM in BM. Thirdly an over-growth pattern was noted in one patient with refractory ALL. In 49 cases where liquid suspension cultures of BM were performed, 4 had a normal-growth pattern and 42 had apoptotic cells and/or few residual granulocytic/monocytic cells after 7 days of culture. However, in both B cell ALL cases and in 1 refractory T cell ALL case with hyperleukocytosis, repetitive liquid suspension cultures of BM and PB consistently revealed an extensive growth of lymphoblasts. Thus, an over-growth pattern in either the BM CFU-GM assay or liquid suspension culture of BM or PB in children with ALL at diagnosis may indicate a refractory or aggressive disease. A low-growth pattern in the BM CFU-GM assay in children with ALL at diagnosis probably predicts a favorable outcome.

Standardization of the CFU-GM Assay Using Hematopoietic Growth Factors

The colony-forming unit-granulocyte-macrophage (CFU-GM) assay is used commonly to assess adequacy of progenitor number in bone marrow transplantation. The assay is poorly standardized, resulting in variability of results between and within laboratories. We assessed three variables that contribute to the lack of standardization. The colony-stimulating activity of human placental-conditioned medium (HPCM) was compared with combinations of recombinant hematopoietic growth factors (HGF) in 5 normal bone marrow donors. A protocol for batch testing of fetal calf serum (FCS) is described. In addition, a rigid training program has been introduced to minimize interstaff and intrastaff variability in the counting of colonies. We show that a five-factor combination of interleukin-3 (IL-3), IL-6, granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage CSF (GM-CSF), and stem cell factor (SCF) produces a mean increase of 85% in colony number. Some combinations of three HGF produce similar growth to HPCM, and all four HGF combinations are equivalent or superior to HPCM. Batch testing of FCS shows variability between batches. We show significant interstaff and intrastaff variability between a new and experienced staff member that improves following a period of training. In summary, the use of recombinant HGF in association with a rigorous program of batch testing of FCS and staff training results in a CFU-GM assay that can be standardized between laboratories.

The effect of the chemokine rhMIP-1 alpha, and a non-aggregating variant BB-10010, on blast cells from patients with acute myeloid leukaemia.

The effects of recombinant macrophage inflammatory protein 1 alpha (rhMIP-1 alpha) on the proliferation of leukaemic blast cells from patients with acute myeloid leukaemia was assessed. Using the previously described [3H]thymidine incorporation index assay, the response of autonomous and growth factor responsive AML blast cells to the chemokine rhMIP-1 alpha was measured. In the case of autonomous proliferators, rhMIP-1 alpha had no inhibitory effect on [3H]thymidine incorporation and in 4/6 cases [3H]-thymidine incorporation was stimulated by rhMIP-1 alpha. In the presence of stem cell factor (SCF), a majority (8/9) of the samples which responded to this growth factor were inhibited when rhMIP-1 alpha was included in the assay medium. Similar results were obtained with GM-CSF-responsive samples; however, when these two cytokines were combined, only 3/14 were significantly inhibited. In the presence of human placental conditioned medium (HPCM), rhMIP-1 alpha significantly inhibited [3H]thymidine incorporation in only 2/10 of HPCM-responsive samples. In methylcellulose assays rhMIP-1 alpha had no consistent effect on colony/cluster formation in the presence of either GM-CSF + SCF or HPCM. Similar results were obtained with BB-10010, a mutant of rhMIP-1 alpha which has defined aggregation properties in solution. These data suggest that autonomously proliferating AML cells, and also some AML samples which require cytokines to proliferate, are non-responsive to the growth inhibitors rhMIP-1 alpha and BB-10010 in the presence of multiple growth factors.

Purification of a ligand for the EPH-like receptor HEK using a biosensor-based affinity detection approach.

Advances in screening technologies allowing the identification of growth factor receptors solely by virtue of DNA or protein sequence comparison call for novel methods to isolate corresponding ligand growth factors. The EPH-like receptor tyrosine kinase (RTK) HEK (human EPH-like kinase) was identified previously as a membrane antigen on the LK63 human pre-B-cell line and overexpression in leukemic specimens and cell lines suggested a role in oncogenesis. We developed a biosensor-based approach using the immobilized HEK receptor exodomain to detect and monitor purification of the HEK ligand. A protein purification protocol, which included HEK affinity chromatography, achieved a 1.8 X 10(6)-fold purification of an approximately 23-kDa protein from human placental conditioned medium. Analysis of specific sHEK (soluble extracellular domain of HEK) ligand interactions in the first and final purification steps suggested a ligand concentration of 40 pM in the source material and a Kd of 2-3 nM. Since the purified ligand was N-terminally blocked, we generated tryptic peptides and N-terminal amino acid sequence analysis of 7 tryptic fragments of the S-pyridylethylated protein unequivocally matched the sequence for AL-1, a recently reported ligand for the related EPH-like RTK REK7 (Winslow, J.W., Moran, P., Valverde, J., Shih, A., Yuan, J.Q., Wong, S.C., Tsai, S.P., Goddard, A., Henzel, W.J., Hefti, F., Beck, K.D., & Caras, I.W. (1995) Neuron 14, 973-981). Our findings demonstrate the application of biosensor technology in ligand purification and show that AL-1, as has been found for other ligands of the EPH-like RTK family, binds more than one receptor.

Modulation of prolactin secretion in human myometrium by cytokines

Prolactin (PRL) secretion and PRL mRNA expression in human myometrial expiant cultures was inhibited by the addition of human placental conditioned medium (HPCM). After 3 days treatment with 5% HPCM PRL secretion was reduced to 24% of control values ( P < 0.001). The effect persisted even after removal of progesterone, which suppresses myometrial PRL production, from the HPCM. In search for additional regulatory substances present in the uteroplacental unit, we tested a number of growth factors and cytokines known to affect pituitary PRL secretion. Treatment with endothelin-3 (ET-3) at a dose of 10 −6 M was found to increase PRL release by 20% over 3 days ( P < 0.05) whereas interleukin-6 (IL-6) showed no effect on PRL levels. Epidermal growth factor, vasoactive intestinal peptide and interferon-α (IFN-α) were inhibitory. Interleukin-4 (IL-4) was the most potent inhibitor of PRL expression in myometrial tissue, causing a reduction of secreted PRL to less than 50% of controls after 3 days at a dose of ≥ 5 ng/ml ( P < 0.001) and a concomitant reduction of PRL mRNA levels. These results demonstrate a modulation of PRL expression in the myometrium by locally present factors.

Autocrine/Paracrine Regulation of Prolactin Release from Human Decidual Cellsa

Studies from this laboratory indicate that the synthesis and release of prolactin from human decidual cells are regulated by factors released by the placenta, decidua and fetal membranes. A 23.5 kD protein (decidual prolactin-releasing factor, PRL-RF) has been purified to homogeneity from human placental tissue and placental conditioned medium. The releasing factor stimulates an acute release of prolactin that occurs within the first few minutes of exposure and a prolonged release, secondary to new hormone synthesis, that begins about 6-8 hours later. In addition, the synthesis and release of decidual prolactin are stimulated by IGF-I, insulin and relaxin, each acting through distinct plasma membrane receptors. In contrast, the synthesis and release of decidual prolactin are inhibited by arachidonic acid, lipocortin I and a 35-45 kD decidual protein (prolactin-releasing inhibitory factor) that has been partially purified from decidual conditioned medium. Studies of the second messengers involved in the regulation of decidual prolactin release strongly suggest that decidual prolactin release may be mediated, at least in part, by activation of phosphoinositide metabolism and stimulation of adenylate cyclase. The demonstration that the synthesis and release of decidual prolactin are regulated by PRL-RF, IGF-I, insulin, relaxin, arachidonic acid, PRL-IF and lipocortin I strongly suggests that there is novel autocrine/paracrine feedback regulation between the placenta, fetal membranes, and decidua in the regulation of decidual prolactin.

ヒト口腔へん平上皮癌における制癌剤感受性試験の基礎的研究 Ｈｕｍａｎ Ｐｌａｃｅｎｔａｌ Ｃｏｎｄｉｔｉｏｎｅｄ Ｍｅｄｉｕｍのコロニー増殖刺激とその有効成分の解析

In order to improve human tumor clonogenic assay (HTCA) that is in vitro chemosensitivity test for anticancer drugs, human placental conditioned medium (HPCM) was applied to HTCA using double soft agar system on human oral squamous cell carcinomas (SCC).Human oral SCC growth on cultured cell lines, surgical specimens and cancer xenografts in nude mice were significantly stimulated by HPCM, so that HPCM was identified as the useful growth factor for human oral SCC.Furthermore the author tried to analyze the growth promoting factors contained in HPCM. Human chorionic gonadotropin (hCG) and its α and β subunits that were included in HPCM promoted colony formations. In one of four human oral SCC cell lines, the transcription of hCGβ mRNA was identified by Northern blot analysis and hCGβ was stained by immunohistochemical method.These results suggest that hCG or hCG like substances in HPCM can promote in vitro growth of human oral SOC.

2′,3′-Dideoxycytidine Preferentially Inhibits in vitro Growth of Granulocyte-Macrophage Colony-Forming Cells from Patients with Chronic Myeloid Leukemia

The effect of three nucleoside analogs, including 2-methyl-2'-deoxyadenosine (MDA), 5-amino-2'-deoxyuridine (ADU) and 2',3'-dideoxycytidine (DDC) on colony formation from unfractionated human bone marrow obtained from volunteers expressing parameters typical for normal cells (NBM) and from patients with the diagnosis of chronic myeloid leukemia (CMLBM) was observed. For the clonal growth of granulocyte-macrophage colony-forming cells (GM-CFC), a semisolid fibrin clot culture medium supplemented with 20% fetal bovine serum and 10% human placental conditioned medium was used. DDC has been shown to be at least a 10-fold more potent inhibitor for the growth of GM-CFC from CMLBM than from NBM. On the other hand, the effect of MDA and ADU on CMLBM did not differ markedly from the effect on NBM. These results suggest that DDC inhibits preferentially progenitor cells from CMLBM.

Granulocyte/macrophage colony-forming units from cord blood of premature and full-term neonates: its role in ontogeny of human hemopoiesis.

It is still uncertain whether the yolk sac is the only origin of hemopoietic stem cells during fetal development. We studied the level of circulating granulocyte/macrophage colony-forming unit (CFU-GM) from the 23rd week of gestation to fullterm, trying to delineate its role in the ontogeny of human hemopoiesis. Cord blood samples were collected from 45 healthy premature neonates and 91 healthy full-term neonates. CFU-GM assays were performed using a single agar layer system with human placental conditioned medium as a source of colony stimulating activity. The mean numbers of colonies produced from the cord blood samples of the premature and full-term neonates were 116 +/- 185 (SD) and 96 +/- 113/2 x 10(5) mononuclear cells, respectively. There was no statistical difference between the numbers of colonies of the two groups (Mann-Whitney test, p greater than 0.05). These results indicate that the level of circulating CFU-GM from the 23rd week of gestation to full term is constantly high and add credence to the assumption that CFU-GM are produced not only from the yolk sac but also from other hemopoietic sites.

Evidence for interactions between monocytes and natural killer cells in the regulation of in vitro hemopoiesis.

The role of accessory cells in modulation of in vitro hemopoiesis was studied using C-mediated lysis with mAb of differing specificities. One such antibody, 25E11, which bound to all NK cells and a subset of monocytes, consistently led to enhancement of in vitro hemopoiesis when 25E11+ cells were depleted by complement or the FACS. In cultures maximally stimulated by erythropoietin and human placental conditioned medium, depletion of 25E11+ cells from beta-thalassemic PBMC resulted in up to a fourfold enhancement of multi-potential and pure erythroid colonies and a twofold enhancement of non-erythroid colonies when compared with C-only treated cells. This enhancement of in vitro hemopoiesis was also observed with cells from normal bone marrow, cord blood, and peripheral blood. The enhancement of in vitro hemopoiesis was abrogated by removal of either adherent cells or monocytes using Leu M3 antibody and C lysis. The data presented herein suggest that NK cells and a subset of monocytes may exert a negative regulatory control on both granulopoiesis and erythropoiesis. Consequently, the number of progenitor and multipotential cells in cultures of unfractionated cell populations may be greatly underestimated.

Fractionation of Subsets of BFU-E From Normal Human Bone Marrow: Responsiveness to Erythropoietin, Human Placental-Conditioned Medium, or Granulocyte-Macrophage Colony-Stimulating Factor

Normal human bone marrow mononuclear cells were fractionated by differential adherence, immunomagnetic separation, and fluorescence-activated cell sorting (FACS). The resultant fractionated cells were cultured in semisolid medium to monitor the presence of BFU-E, Mix-CFC, and nonerythroid CFC. Two populations of cells were recovered on the basis of binding by the monoclonal antibody (MoAb) RFB-1. One of these populations contained BFU-E that were stimulated only by erythropoietin (Epo), whereas the second population contained BFU-E responsive to Epo, Epo and recombinant human granulocyte-macrophage colony-stimulating factor (rHGM-CSF), or Epo and human placental-conditioned medium (HPCM). Prior enrichment of clonogenic cells by removal of adherent and Leu-M3+ve, Leu-4+ve, Leu-7+ve, B1+ve, WEMG1+ve, and Glycophorin A+ve cells, followed by FACS fractionation on the basis of RFB-1 binding, consistently resulted in recoveries of BFU-E, Mix-CFC, and nonerythroid CFC of greater than 100% (up to 800%). These procedures also resulted in enrichment of up to 200-fold and frequencies of 1:6 for BFU-E, 1:5 for CFC, and 1:130 for Mix-CFC.

Fractionation of subsets of BFU-E from normal human bone marrow: responsiveness to erythropoietin, human placental-conditioned medium, or granulocyte-macrophage colony-stimulating factor

Normal human bone marrow mononuclear cells were fractionated by differential adherence, immunomagnetic separation, and fluorescence- activated cell sorting (FACS). The resultant fractionated cells were cultured in semisolid medium to monitor the presence of BFU-E, Mix-CFC, and nonerythroid CFC. Two populations of cells were recovered on the basis of binding by the monoclonal antibody (MoAb) RFB-1. One of these populations contained BFU-E that were stimulated only by erythropoietin (Epo), whereas the second population contained BFU-E responsive to Epo, Epo and recombinant human granulocyte-macrophage colony-stimulating factor (rHGM-CSF), or Epo and human placental-conditioned medium (HPCM). Prior enrichment of clonogenic cells by removal of adherent and Leu-M3+ve, Leu-4+ve, Leu-7+ve, B1+ve, WEMG1+ve, and Glycophorin A+ve cells, followed by FACS fractionation on the basis of RFB-1 binding, consistently resulted in recoveries of BFU-E, Mix-CFC, and nonerythroid CFC of greater than 100% (up to 800%). These procedures also resulted in enrichment of up to 200-fold and frequencies of 1:6 for BFU-E, 1:5 for CFC, and 1:130 for Mix-CFC.

Cytogenetic evidence of clonal proliferation of leukemic progenitor cells from patients with acute promyelocytic leukemia (APL)

We have studied in-vitro growth of leukemic progenitor cells (L-CFU) in ten patients with acute promyelocytic leukemia (APL). All patients showed consistently an extraordinarily high incidence of cluster formation under the stimulation of human placental conditioned medium (HPCM) and/or phytohemagglutinin-stimulated leukocyte conditioned medium (PHA-LCM). Cytogenetic analyses of clusters or colonies disclosed the presence of a 15;17 translocation. These findings may represent the close relationship between specific chromosomal aberration, t(15;17), and the growth pattern of L-CFU of APL in vitro.

Heterogeneous colony forming ability in vitro of the abnormal clone-derived granulocyte-macrophage precursors in myelodysplastic syndromes

The clonal origin of granulocyte-macrophage colony forming cells (CFU-GM) in the myelodysplastic syndrome (MDS) was cytogenetically studied. Chromosome analysis was carried out on single GM-colonies from six patients with MDS, whose bone marrow cells had chromosome abnormalities. Abnormal clone-derived CFU-GM were grown in four patients under the presence of human placental conditioned medium. In the remaining two, all analysed colonies revealed a normal karyotype, although the majority of metaphase cells showed an abnormal karyotype in bone marrow preparations. These results indicate that the abnormal clone-derived CFU-GM in MDS have a clone-by-clone variation in colony forming ability in vitro.

Purification and Properties of Bacterially Synthesized Human Granulocyte-Macrophage Colony Stimulating Factor

Human granulocyte-macrophage colony stimulating factor (GM-CSF) has been synthesized in high yield using a temperature inducible plasmid in Escherichia coli. The human GM-CSF is readily isolated from the bacterial proteins because of its differential solubility and chromatographic properties. The bacterially synthesized form of the human GM-CSF contains an extra methionine residue at position 1, but otherwise it is identical to the polypeptide predicted from the cDNA sequence. The specific activity of 2.9 X 10(7) units/mg of protein for purified bacterially synthesized human GM-CSF indicates that despite the lack of glycosylation, the molecule is substantially in its native conformation. This molecule stimulated the same number and type of both seven- and 14-day human bone marrow colonies as the CSF alpha preparation from human placental conditioned medium. Human GM-CSF had no activity on murine bone marrow or murine leukemic cells. There was no detectable, direct stimulation of adult human erythroid burst forming units (BFU-E) by the bacterially synthesized human GM-CSF. Although impure preparations containing native human GM-CSF (eg, human placental conditioned medium) stimulated the formation of mixed colonies, even in the presence of erythropoietin, the bacterially synthesized human GM-CSF failed to stimulate the formation of mixed colonies from adult human bone marrow cells. The bacterially synthesized human GM-CSF increased N-formyl-methionyl-leucyl-phenylalanine (FMLP)-induced superoxide production and lysozyme secretion. Antibody-dependent cytotoxicity and phagocytosis by human neutrophils was stimulated by the bacterially synthesized human GM-CSF and eosinophils were also activated in the antibody-dependent cytotoxicity assay.

Purification and properties of bacterially synthesized human granulocyte-macrophage colony stimulating factor

Human granulocyte-macrophage colony stimulating factor (GM-CSF) has been synthesized in high yield using a temperature inducible plasmid in Escherichia coli. The human GM-CSF is readily isolated from the bacterial proteins because of its differential solubility and chromatographic properties. The bacterially synthesized form of the human GM-CSF contains an extra methionine residue at position 1, but otherwise it is identical to the polypeptide predicted from the cDNA sequence. The specific activity of 2.9 X 10(7) units/mg of protein for purified bacterially synthesized human GM-CSF indicates that despite the lack of glycosylation, the molecule is substantially in its native conformation. This molecule stimulated the same number and type of both seven- and 14-day human bone marrow colonies as the CSF alpha preparation from human placental conditioned medium. Human GM-CSF had no activity on murine bone marrow or murine leukemic cells. There was no detectable, direct stimulation of adult human erythroid burst forming units (BFU-E) by the bacterially synthesized human GM-CSF. Although impure preparations containing native human GM-CSF (eg, human placental conditioned medium) stimulated the formation of mixed colonies, even in the presence of erythropoietin, the bacterially synthesized human GM-CSF failed to stimulate the formation of mixed colonies from adult human bone marrow cells. The bacterially synthesized human GM-CSF increased N-formyl-methionyl-leucyl- phenylalanine (FMLP)-induced superoxide production and lysozyme secretion. Antibody-dependent cytotoxicity and phagocytosis by human neutrophils was stimulated by the bacterially synthesized human GM-CSF and eosinophils were also activated in the antibody-dependent cytotoxicity assay.

A characteristic CFU-GM growth pattern in acute promyelocytic leukemia

Bone marrow and/or peripheral blood cells from 12 patients with acute promyelocytic leukemia (APL) were cultured in soft agar or methylcellulose in the presence of 15% human placental conditioned medium as a source of colony stimulating factor. Buffy coat cells, taken from ten patients when APL was diagnosed, produced a growth pattern in soft agar that was characterized by a high incidence of small, relatively uniform clusters of promyelocytes, which, when stained in situ, reacted strongly with myeloperoxidase, Sudan black B and chloroacetate esterase. In six cases, the leukemic origin of the cluster forming cells was demonstrated by the presence of the t(15;17) in these cells. During periods of complete remission the small clusters were replaced by larger and more diverse aggregates which had a normal karyotype. At relapse the small cluster growth pattern returned. The growth pattern of small clusters is more commonly associated with APL than with other types of acute myeloid leukemia.

Fractionation of CSF activities from human placental conditioned medium.

Colony stimulating factors (CSFs) are required for the survival, proliferation and differentiation of hemopoietic progenitor cells in vitro and possibly in vivo. Recently, several human CSFs have been purified and molecularly cloned from human tumor cell lines. These include granulocyte colony stimulating factor (G-CSF), from the bladder carcinoma cell line 5637 [1, 2] and the squamous cell carcinoma cell line CHU-2 [3], and granulocyte-macrophage colony stimulating factor (GM-CSF), from the Mo T-lymphoblast cell line [4, 5] and the monocytic cell line U937 (personal communication, Dr. J. DeLamarter). In addition, human erythroid potentiating activity (EPA) has been purified and molecularly cloned from the Mo T-lymphoblast cell line [6, 7].

Murine eosinophil differentiation factor. An eosinophil-specific colony-stimulating factor with activity for human cells.

A purified murine lymphokine, eosinophil differentiation factor (EDF), was found to be a selective stimulus for the clonal proliferation and differentiation of murine eosinophil progenitor cells, establishing it as the murine eosinophil colony-stimulating factor (Eo-CSF). EDF was also active on human eosinophil progenitors and mature blood eosinophils, but had no effect on neutrophil or macrophage precursor cells, nor on blood neutrophils. In culture of human bone marrow cells, EDF stimulated equal numbers and equal sizes of eosinophil colonies to develop when compared with human placental conditioned medium, a source of human CSFs, suggesting that all responsive progenitor cells were stimulated. Clone transfer experiments and the linear relationship between number of bone marrow cells plated and colonies produced confirmed that the action of EDF was directly on eosinophil progenitor cells. EDF increased the capacity of human blood eosinophils, but not neutrophils, to kill antibody-coated tumor cells and to phagocytose serum-opsonized yeast cells. This functional activation was associated with the enhanced expression of functional antigens (GFA-1, GFA-2, and the receptor for C3bi) on eosinophils. The possession by EDF (Eo-CSF) of all the properties expected of a human eosinophil CSF raises the possibility that a human analog of this molecule exists, and is involved in the regulation of production and function of human eosinophils in vivo.