Cloning of the low-affinity murine granulocyte-macrophage colony-stimulating factor receptor and reconstitution of a high-affinity receptor complex

A cDNA clone (clone 71) that encodes a low-affinity receptor for murine granulocyte-macrophage colony-stimulating factor (GM-CSF) has been isolated by direct expression. This molecule is the homologue of the human GM-CSF receptor alpha subunit, although homology between these molecules is surprisingly low (less than 35% amino acid identity). The cDNA encodes a polypeptide of 387 amino acids, which contains the conserved features of the hematopoietin receptor superfamily. When expressed in COS-7 cells, this clone encodes a protein that binds radiolabeled murine GM-CSF with low affinity. Coexpression of clone 71 with a cDNA corresponding to a low-affinity interleukin 3 (IL-3) receptor (AIC2A) did not alter the affinity of binding of either GM-CSF or IL-3. However, coexpression of clone 71 with the IL-3 receptor-related cDNA AIC2B generated high-affinity binding sites for murine GM-CSF but not murine IL-3. These studies show that clone 71 and AIC2B are capable of forming an alpha beta complex capable of binding murine GM-CSF with high affinity, while AIC2A appears not to be a component of the murine GM-CSF receptor.

A GM-colony-stimulating factor (CSF) activated ribonuclease system transregulates M-CSF receptor expression in the murine FDC-P1/MAC myeloid cell line

The murine myeloid precursor cell line FDC-P1/MAC simultaneously expresses receptors for multi-colony-stimulating factor (CSF), granulocyte-macrophage (GM)-CSF, and macrophage (M)-CSF. Growth of FDC-P1/MAC cells in either multi-CSF or GM-CSF results in the posttranscriptional suppression of M-CSF receptor (c-fms proto-oncogene) expression. We use the term transregulation to describe this control of receptor expression and have further characterized this regulatory process. The removal of FDC-P1/MAC cells from GM-CSF stimulation resulted in the re-expression of c-fms mRNA independent of M-CSF stimulation and new protein synthesis. Switching FDC-P1/MAC cells from growth in M-CSF to GM-CSF caused the selective degradation of c-fms mRNA within 6 h after factor switching. Blocking protein synthesis or gene transcription with metabolic inhibitors effectively prevented GM-CSF stimulated degradation of c-fms mRNA. These results suggest that the transregulation of c-fms transcripts by GM-CSF requires the transcriptional activation of a selective mRNA degradation factor. In vitro analysis, the use of cytoplasmic cell extracts, provided evidence that a ribonuclease is preferentially active in GM-CSF stimulated cells, although the specificity for mRNA degradation in vitro is broader than seen in vivo. Together, these data suggest that GM-CSF can dominantly transregulate the level of c-fms transcript through the transcriptional activation of a ribonuclease degradation system.

Identification of a novel low-affinity receptor for human interleukin-7

Human recombinant interleukin-7 (IL-7) was labeled with biotin and used to examine IL-7 receptor (IL-7R) expression and regulation on human primary hematopoietic cells, the monocytoid line THP1, and a range of B- and pre-B-celi lines by flow cytometry. A strong intensity of staining was observed using relatively high (greater than 1 x 10(-7) mol/L) concentrations of biotinylated IL-7 on the majority of cell types examined. This reactivity, which could be effectively competed with excess unlabeled IL-7, did not correlate with either mRNA levels for the cloned receptor or with estimates of IL-7R expression determined by [125I]IL-7 binding. Staining of cells with a titration of biotinylated IL-7 showed, at concentrations greater than 1 x 10(-7) mol/L binding with a Ka in the range of 1 x 10(6) mol/L-1, to 1 x 10(7) mol/L-1, an affinity 100 to 1,000 times lower than that reported for the cloned IL-7 receptor. Further data suggesting the existence of a distinct low- affinity IL-7R were provided by two antibodies specific for the cloned IL-7R. Staining with these monoclonal antibodies (MoAbs) correlated with both IL-7R mRNA levels and receptor expression determined by [125I]IL-7 binding, but was not compatible with the distribution of reactivity seen with biotinylated IL-7. Using tritiated biotin to label IL-7, it was estimated that the total number of IL-7 binding sites on the cell lines examined ranged from 1 x 10(4) to at least 5 x 10(5)/cell. Cross-linking studies showed that [125I]IL-7 associated with two major proteins of approximately 62 Kd and 70 Kd on the surface of RPMI 1788 and THP1 cells, in contrast to the 75- to 80 Kd molecule characteristic of the previously cloned receptor, expressed on the surface of Daudi cells. Proliferation of THP1 cells, expressing only the low-affinity form of IL-7R and lacking detectable IL-7R mRNA, could be inhibited by the addition of IL-7 in a concentration-dependent fashion, indicating that, at least on this cell line, binding of IL-7 with a Ka of 1 x 10(6) mol/L-1 to 1 x 10(7) mol/L-1 can transduce a biological signal. Taken together, the data contained in this report demonstrate the existence of a low-affinity IL-7R, expressed in high numbers on hematopoietic cells of different lineages, which is the product of a gene distinct from that encoding the cloned IL-7R.

Differential binding of IL-3 and GM-CSF to human monocytes

Human monocytes respond to IL-3 and GM-CSF with a similar range of functional activities, and at similar cytokine concentrations. We have recently shown, however, that the rate of monocyte activation is greater in response to GM-CSF than to IL-3. In order to understand the basis of this phenomenon we investigated the interaction of IL-3 and GM-CSF with their surface receptors by means of kinetic binding experiments. 125I-GM-CSF showed very rapid association to monocytes at 37 degrees C, with a half-time of only 40 sec. The pattern of binding with this ligand was complex, with a decline in overall cell-associated radioactivity after 2 min of incubation. In contrast, 125I-IL-3 showed slower association, with a half-time at 37 degrees C of 2.5 min. The different rates of association correlated well with the different rates of cell activation induced by the two cytokines. On the other hand, rates of internalisation were similar for the two cytokines, with half-times of 14-15 min. Competition binding experiments performed under high affinity conditions showed that IL-3 and GM-CSF cross-competed for binding on the surface of monocytes. In contrast, under low affinity conditions IL-3 did not compete for 125I-GM-CSF binding while GM-CSF was a strong competitor of 125I-IL-3 binding. In quantitative inhibition experiments GM-CSF showed inhibitory effects on low affinity 125I-IL-3 binding at lower concentrations than those needed with unlabelled IL-3. It is suggested that current models of IL-3/GM-CSF receptor interactions need to be revised in order to accommodate the unique pattern of competition on human monocytes presented here.

Interleukin-5, interleukin-3, and granulocyte-macrophage colony-stimulating factor cross-compete for binding to cell surface receptors on human eosinophils

Human interleukin (IL)-5 receptors were characterized by means of binding studies using bioactive 125I-labeled IL-5. Of purified primary myeloid cells, eosinophils and basophils but not neutrophils or monocytes expressed surface receptors for IL-5. Binding studies showed that eosinophils expressed a single class of high affinity receptors (Ka = 1.2 x 10(10) M-1) with the number of receptors being small (less than 1000 receptors/cell) and varying between individuals. Among several cell lines examined only HL-60 cells showed detectable IL-5 receptors which were small in numbers (200 receptors/cell) and also bound 125I-IL-5 with high affinity. The binding of IL-5 was rapid at 37 degrees C while requiring several hours to reach equilibrium at 4 degrees C. Specificity studies revealed that the two other human eosinophilopoietic cytokines IL-3 and granulocyte-macrophage colony-stimulating factor (GM-CSF) inhibited the binding of 125I-IL-5 to eosinophils. No competition was observed by other eosinophil activating or nonactivating cytokines. The inhibition of 125I-IL-5 binding by IL-3 and GM-CSF was partial up to a concentration of competitor of 10(-7) M with GM-CSF consistently being the stronger competitor. Converse experiments using IL-5 as a competitor revealed that this cytokine inhibited the binding of 125I-IL-3 and of 125I-GM-CSF in some but not all the individuals tested, perhaps reflecting eosinophil heterogeneity in vivo. Cross-linking experiments on HL-60 cells demonstrated two IL-5-containing complexes of Mr 150,000 and Mr 80,000 both of which were inhibited by GM-CSF. The competition between IL-5, IL-3, and GM-CSF on the surface of mature eosinophils may represent a unifying mechanism that may help explain the common biological effects of these three eosinophilopoietic cytokines on eosinophil function. This unique pattern of competition may also be beneficial to the host by preventing excessive eosinophil stimulation.

Hybrid cytokines as hematopoietic growth factors

A large body of in vitro and in vivo data suggests that combinations of cytokines provide the most effective mechanism for stimulating multilineage acceleration of hematopoiesis. Creation of a granulocyte-macrophage colony-stimulating factor (GM-CSF)/interleukin 3 (IL-3) fusion protein has yielded a single therapeutic which has enhanced biological activity in comparison to the individual cytokines from which it is composed. In vivo studies with this fusion protein (PIXY321) suggest that it may provide a means to accelerate both neutrophil and platelet recovery in clinical settings in which hematopoiesis is suppressed. The biology of PIXY321 and the potential for other fusion proteins is discussed.

Regulation of alloreactivity in vivo by IL-4 and the soluble IL-4 receptor

Although numerous in vitro studies have demonstrated that cytokines are involved in the generation of alloreactive effector cells, the role of these regulatory substances in vivo is less well defined. We have recently cloned and expressed cDNAs encoding both membrane bound and soluble forms of the murine IL-4R. The effects of murine rIL-4 and a recombinant, soluble, extracellular portion of the murine IL-4R soluble(s) IL-4R on the generation of alloresponsiveness in vivo were evaluated by measuring the lymphoproliferative response to a localized injection of allogeneic cells and the survival of cardiac allografts. Administration of IL-4 to BALB/c mice resulted in a slight augmentation of the anti-C57BL/6 lymphoproliferative response compared to that occurring in control, mouse serum albumin-(MSA) treated mice. In contrast, the sIL-4R suppressed this response to allogeneic cells in a dose-dependent manner, with a dose of 50 micrograms/kg/day causing nearly complete inhibition of the response as compared to the response observed in controls. The inhibitory effect of sIL-4R was reversed by simultaneous administration of IL-4. A neutralizing antibody against IL-4 (11B11) and another against the IL-4R (M1) were also effective inhibitors of the response when given at 100- to 1000-fold higher concentrations than the amount of sIL-4R required to inhibit the response. In cardiac allograft experiments, BALB/c mice were engrafted with newborn C57BL/6 hearts in the ear pinnae and treated with sIL-4R (50 micrograms/kg) or MSA. Such allografts survived an average of 4 days longer in sIL-4R-treated mice than in MSA-treated controls. In conclusion, neutralization of IL-4 inhibits alloresponsiveness in vivo. These results confirm a regulatory role for this pleiotropic cytokine in allograft rejection and suggest a therapeutic value for IL-4 antagonists alone or in combination with other immunosuppressive regimens.

Regulation of alloreactivity in vivo by IL-4 and the soluble IL-4 receptor

Although numerous in vitro studies have demonstrated that cytokines are involved in the generation of alloreactive effector cells, the role of these regulatory substances in vivo is less well defined. We have recently cloned and expressed cDNAs encoding both membrane bound and soluble forms of the murine IL-4R. The effects of murine rIL-4 and a recombinant, soluble, extracellular portion of the murine IL-4R soluble(s) IL-4R on the generation of alloresponsiveness in vivo were evaluated by measuring the lymphoproliferative response to a localized injection of allogeneic cells and the survival of cardiac allografts. Administration of IL-4 to BALB/c mice resulted in a slight augmentation of the anti-C57BL/6 lymphoproliferative response compared to that occurring in control, mouse serum albumin-(MSA) treated mice. In contrast, the sIL-4R suppressed this response to allogeneic cells in a dose-dependent manner, with a dose of 50 micrograms/kg/day causing nearly complete inhibition of the response as compared to the response observed in controls. The inhibitory effect of sIL-4R was reversed by simultaneous administration of IL-4. A neutralizing antibody against IL-4 (11B11) and another against the IL-4R (M1) were also effective inhibitors of the response when given at 100- to 1000-fold higher concentrations than the amount of sIL-4R required to inhibit the response. In cardiac allograft experiments, BALB/c mice were engrafted with newborn C57BL/6 hearts in the ear pinnae and treated with sIL-4R (50 micrograms/kg) or MSA. Such allografts survived an average of 4 days longer in sIL-4R-treated mice than in MSA-treated controls. In conclusion, neutralization of IL-4 inhibits alloresponsiveness in vivo. These results confirm a regulatory role for this pleiotropic cytokine in allograft rejection and suggest a therapeutic value for IL-4 antagonists alone or in combination with other immunosuppressive regimens.

The interleukin-4 receptor gene (IL4R) maps to 16p11.2-16p12.1 in human and to the distal region of mouse chromosome 7

The chromosomal location of both the human and the mouse interleukin-4 receptor (IL4R) genes have been determined. The human gene was localized to 16p11.2-16p12.1 by in situ hybridization and confirmed by Southern blot analysis of DNA from a panel of mouse-human hybrid somatic cell lines. The mouse homolog was positioned in the distal region of chromosome 7 by interspecific backcross analysis. The results suggest that the IL4R locus is unlinked to other members of the hematopoietin receptor family. Interestingly, the position on human chromosome 16 suggests that the IL4R may be a candidate for rearrangements, as 12;16 translocations are often associated with myxoid liposarcomas.

Inhibition of human monocyte adhesion by interleukin-4

The adhesion of monocytes to vascular surfaces is central to inflammation and atherogenesis; however, very little is known about regulatory factors that can prevent these processes. Here we report the inhibition of human monocyte adhesion to human endothelial layers and plastic by interleukin-4 (IL-4), a T-cell-derived glycoprotein with pleiotropic activities. The inhibitory effects of IL-4 were seen with basal and cytokine-stimulated monocyte adhesion, were apparent at low concentration, and were abolished by inactivating IL-4. No direct toxic effect of IL-4 on monocytes was detected. Inhibition of adhesion was accompanied by small increases in monocyte surface expression of the leukocyte-functional antigen group of adhesion structures, suggesting that absolute levels of expression may be less important than the functional status of such molecules in the regulation of monocyte adhesion. In addition, inhibition by IL-4 of cytokine-stimulated monocyte adhesion was not associated with changes in the surface expression of cytokine receptors. These results suggest a role for IL-4 in the regulation of monocyte adhesion, and may provide for a common mechanism for the inhibitory effects of IL-4 on monocyte function.

Characterization and pharmacokinetic parameters of recombinant soluble interleukin-4 receptor

The interleukin-4 receptor (IL-4R) is expressed as a 140-Kd membrane glycoprotein that binds IL-4 with high affinity. Recently, cDNA clones for the murine IL-4R have been isolated. One clone encodes an integral membrane protein, while another encodes a protein in which translation is terminated before the transmembrane region, thus producing a soluble form of the IL-4R (sIL-4R). HeLa cell clones overexpressing sIL-4R were isolated using a novel filter-overlay and 125I-IL-4 ligand binding technique. Quantitative analysis demonstrated that the kinetics and affinity of IL-4 binding to the recombinant sIL-4R were similar to the native membrane-bound IL-4R. As low doses of sIL-4R specifically inhibited IL-4-induced proliferative responses in vitro, sIL-4R biodistribution and elimination parameters were evaluated to assess the pharmacokinetic potential of sIL-4R as a therapeutic agent. Pharmacokinetic studies demonstrated that radiolabeled sIL-4R had a distribution half-life of 9 minutes and an elimination half-life of 2.3 hours following intravenous (IV) administration. When administered by intraperitoneal or subcutaneous (SC) injection, the elimination half-lives were prolonged to 4.2 hours and 6.2 hours, respectively. Although the initial blood level of sIL-4R was reduced if administered by SC injection, the bioavailability was comparable with IV administration. The main sites of sIL-4R elimination were the liver and kidney.

Organization of the murine and human interleukin-7 receptor genes: two mRNAs generated by differential splicing and presence of a type I-interferon-inducible promoter

To better understand the regulation of interleukin-7 receptor (IL-7R) expression, we have pursued a detailed analysis of the structure of the murine and human IL-7R genes. The genes consist of eight exons, the sizes of which are conserved in mouse and human cells, spread out over 24 kbp (murine) and 19 kbp (human). A differential splicing event results in an mRNA encoding a secreted form of the human IL-7R gene. Primer extension and S1 nuclease analysis show a single transcriptional start site for the murine IL-7R gene. The 5'-flanking region of the murine IL-7R gene contains TATA- and CAAT-like sequences. The promoter region also contains a functional interferon regulatory element, to which the interferon-induced nuclear factors IRF-1 and IRF-2 are capable of binding and which is able to confer interferon-inducible expression on a heterologous gene. There are also potential binding sites for the transcription factors AP-1 and AP-2 as well as multiple glucocorticoid response elements. A fusion gene containing 2.5 kb of murine IL-7R 5' regulatory sequence linked to the bacterial chloramphenicol acetyltransferase gene directed expression of chloramphenicol acetyltransferase activity in murine pre-B-cell line 70Z/3 but not in the mouse fibroblast cell line NIH 3T3. Comparison of the murine and human IL-7R exon/intron boundaries with those of other hematopoietin receptor superfamily members whose exon/intron boundaries are also known reveals a conserved evolutionary structure.

Hematopoietic effects of a granulocyte-macrophage colony-stimulating factor/interleukin-3 fusion protein

The common functional characteristics of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3) may be explained by the presence of a subpopulation of cell surface receptors capable of binding both growth hormones. A GM-CSF/IL-3 fusion protein (pIXY 321) was produced in a yeast expression host. Receptor binding studies with HL-60, JM-1, AML-193, and KG-1 cell lines suggested that the GM-CSF and IL-3 regions had adopted a native conformation within the fusion protein. The fusion protein also exhibited enhanced biologic activity compared with GM-CSF or IL-3 in assays of normal, primary human hematopoietic progenitor cells. pIXY 321 may offer significant clinical advantages over the individual cytokines.

Interleukin 4 alone or in combination with interleukin 1 stimulates 3T3 fibroblasts to produce colony-stimulating factors

Colony-stimulating activity (CSA) can be produced by fibroblasts when stimulated by interleukin 1 (IL-1). We show that like IL-1, interleukin 4 (IL-4) can stimulate 3T3 fibroblasts to produce CSA. Biological and molecular analyses show that a significant portion of the CSA is colony-stimulating factor 1 (CSF-1) and granulocyte colony-stimulating factor (G-CSF). CSF-1 production in cells stimulated with a combination of both IL-1 and IL-4 was greater than that observed when cells were stimulated with either cytokine alone. However, the data show a synergistic induction of the expression of high levels of G-CSF mRNA and protein in cells incubated in the presence of both IL-1 and IL-4. The concentration of G-CSF in supernatants from cells stimulated with both IL-1 and IL-4 was at least tenfold higher than that measured in supernatants harvested from cells stimulated with either IL-1 or IL-4 alone. Previous investigations have shown that IL-4 had direct effects on hematopoietic progenitor cell growth. The studies described herein indicate that IL-4 is also involved in the regulation of hematopoiesis in an indirect manner, that is, by playing a role in the regulation of hematopoietic growth factor production.

The IL-4 receptor: biochemical characterization of IL-4-binding molecules in a T cell line expressing large numbers of receptors

Cross-linking of 125I-IL-4 to the surface of cells expressing IL-4R yields as the major IL-4-binding molecules, polypeptide chains with inferred m.w. of approximately 70,000 (p70) and approximately 120,000 to 140,000 (p120-p140). The demonstration that the functional product of the IL-4R cDNA clone has m.w. of approximately 140,000 and that no p70 product is detected in transfected COS-7 cells has led to an uncertainty regarding the nature of p70. To study this issue, we examined the relationship of the IL-4-binding molecules p120 and p70 and, in parallel, attempted to immunoprecipitate p70 from surface and internally labeled cells using IL-4 and two anti-IL-4R antibodies (M1 and M2), bound to Affigel 10, as ligands. Cross-linked complexes containing 125I-IL-4 and p70 or p120 were isolated and digested with chymotrypsin or with V8 protease. Three distinct IL-4-binding peptides could be compared; these were indistinguishable for cross-linked p70 and p120, strongly implying that p70 and p120 were structurally related. Furthermore, immunoprecipitates made with IL-4 or anti-IL-4R-Affigel did not contain p70. This led us to conclude that p70 is a breakdown product of p120. A second IL-4-binding molecule of 40,000 Da (p40) expressing the M1 and M2 epitopes of the IL-4R was detected and appears to be the product of an mRNA coding for the soluble form of the receptor. mRNA for p40 was detected in both the T cell line CT.4R and the mast cell line CFTL.12 using polymerase chain reaction primers unique to this species of message. Pulse-chase studies of IL-4R in [35S] methionine-labeled cells indicates that p40 is derived from a 42,000-Da precursor that is detectable at the end of the pulse period, and thus, further argue that p40 is an independently translated molecule and not a degradation product of p120. Although p40 has been previously shown to be a soluble, truncated form of the receptor, we failed to observe secretion of p40 into the medium by internally labeled CT.4R cells.

The IL-4 receptor: biochemical characterization of IL-4-binding molecules in a T cell line expressing large numbers of receptors

Cross-linking of 125I-IL-4 to the surface of cells expressing IL-4R yields as the major IL-4-binding molecules, polypeptide chains with inferred m.w. of approximately 70,000 (p70) and approximately 120,000 to 140,000 (p120-p140). The demonstration that the functional product of the IL-4R cDNA clone has m.w. of approximately 140,000 and that no p70 product is detected in transfected COS-7 cells has led to an uncertainty regarding the nature of p70. To study this issue, we examined the relationship of the IL-4-binding molecules p120 and p70 and, in parallel, attempted to immunoprecipitate p70 from surface and internally labeled cells using IL-4 and two anti-IL-4R antibodies (M1 and M2), bound to Affigel 10, as ligands. Cross-linked complexes containing 125I-IL-4 and p70 or p120 were isolated and digested with chymotrypsin or with V8 protease. Three distinct IL-4-binding peptides could be compared; these were indistinguishable for cross-linked p70 and p120, strongly implying that p70 and p120 were structurally related. Furthermore, immunoprecipitates made with IL-4 or anti-IL-4R-Affigel did not contain p70. This led us to conclude that p70 is a breakdown product of p120. A second IL-4-binding molecule of 40,000 Da (p40) expressing the M1 and M2 epitopes of the IL-4R was detected and appears to be the product of an mRNA coding for the soluble form of the receptor. mRNA for p40 was detected in both the T cell line CT.4R and the mast cell line CFTL.12 using polymerase chain reaction primers unique to this species of message. Pulse-chase studies of IL-4R in [35S] methionine-labeled cells indicates that p40 is derived from a 42,000-Da precursor that is detectable at the end of the pulse period, and thus, further argue that p40 is an independently translated molecule and not a degradation product of p120. Although p40 has been previously shown to be a soluble, truncated form of the receptor, we failed to observe secretion of p40 into the medium by internally labeled CT.4R cells.

Expression of receptors for interleukin 4 and interleukin 7 on human T cells

Human recombinant interleukin 4 (IL-4) and interleukin 7 (IL-7) have been modified with biotin-N-hydroxysuccinimide and used to examine the expression of human IL-4 and IL-7 receptors (R) on activated peripheral blood T cells by flow cytometry. Freshly isolated T cells expressed only a low level of IL-4R which remained unchanged when cells were cultured in the absence of stimuli. In the presence of IL-4, IL-7, phytohemagglutinin A (PHA) or immobilized CD3 monoclonal antibody the intensity of biotinylated IL-4 staining increased approximately twofold on the majority of cells. A combination of mitogen with either IL-4 or IL-7 caused a considerable increase in IL-4 receptor expression over that seen in the presence of mitogen alone. IL-2 alone failed to induce IL-4R although it was able to cause a significant increase in receptor expression on T cells co-cultured with PHA or CD3. Freshly isolated T cells expressed high levels of IL-7R, as determined by biotinylated IL-7 binding and flow cytometry, which did not change significantly with culture in medium alone. Stimulation with PHA, Concanavalin A (Con A) or CD3 had little effect on the intensity of staining. In contrast, activation with phorbol ester resulted in a decrease in IL-7R expression. Similarly, in the presence of IL-4 or IL-7, but not IL-2, the intensity of staining with biotinylated IL-7 was lowered. Analysis of purified T-cell populations showed that IL-7R were present, and IL-4R could be induced, on both CD4+ and CD8+ populations. Analysis of IL-4 receptor expression by this flow cytometric technique was supported by results from 125I-labeled IL-4 binding and by Northern blot analysis of mRNA levels. Taken together, the results of these studies show that the use of biotinylated cytokines and flow cytometry provides a very sensitive method with which to study the expression and regulation of cytokine receptors.

Identification of a ligand for the c-kit proto-oncogene

We report the purification and N-terminal amino acid sequence of a novel mast cell growth factor, termed MGF, from the supernatants of a murine stromal cell line. A panel of interleukin 3-dependent cell lines were screened for responsiveness to partially purified MGF in [3H]thymidine incorporation assays; proliferative stimulation of these cells in response to MGF correlated with expression of mRNA for the c-kit protooncogene. MGF was shown to be a ligand for c-kit by cross-linking 125I-labeled MGF to c-kit-expressing cells with subsequent immunoprecipitation of the complex with antiserum specific for the C-terminus of c-kit. This establishes MGF as a ligand for the c-kit protein.

Human interleukin-3 inhibits the binding of granulocyte-macrophage colony-stimulating factor and interleukin-5 to basophils and strongly enhances their functional activity

The human T cell-derived cytokines interleukin (IL)-3, granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-5 were examined for their ability to bind specifically to human basophils and to regulate their function. Scatchard analysis of equilibrium binding studies showed that IL-3 and GM-CSF, bound to basophils with apparent dissociation constants (KD) = 8 x 10(-11) M and 3.9 x 10(-11) M, respectively. Specificity studies under conditions that prevent receptor internalization showed that the binding of IL-3, GM-CSF, and IL-5 was not inhibited by tumor necrosis factor (TNF)-alpha, IL-1 beta, interferon (IFN)-gamma, or G-CSF. However, receptors for IL-3, GM-CSF, and IL-5 interacted with each other on the basophil membrane, showing a unique spectrum of cross-reactivity, with IL-3 competing for GM-CSF and IL-5 binding, whereas GM-CSF and IL-5 showed little or no competition for IL-3 binding. In order to relate the binding properties of these cytokines to function, they were tested for their ability to influence basophil histamine release in an IgE/anti-IgE-dependent system. We found a hierarchy in the stimulation of basophil with the order of potency being IL-3 greater than GM-CSF greater than IL-5. In addition, IL-3 stimulated larger amounts of histamine release than GM-CSF or IL-5. The observation that IL-3 interacts with receptors for GM-CSF and IL-5 may have a bearing on its stronger functional effects and suggests a major role for IL-3 in the pathogenesis of hypersensitivity syndromes.

A ceramide analogue inhibits T cell proliferative response through inhibition of glycosphingolipid synthesis and enhancement of N,N-dimethylsphingosine synthesis

The ceramide analogue 1-phenyl-2-(decanoylamino)-3-morpholino-1-propanol (PDMP) (particularly the D-threo isomer, D-PDMP) caused inhibition of cell growth in some types of cells, and this growth-inhibitory effect has been attributed to inhibition of UDP-Glc:Cer beta-Glc transferase, resulting in reduced glycolipid synthesis and increased free ceramide [Inokuch, J., & Radin, N. S. (1987) J. Lipid Res. 28, 565-571; Okada, Y., et al. (1988) FEBS Lett. 235, 25-29]. In view of increasing evidence that the T cell proliferative immune response is modulated by glycosphingolipids (GSLs), the reagent D-PDMP was used to evaluate the role of GSLs in this respect. Con A induced or PHA-induced mitogenesis of C3H/HeJ mouse splenocytes, as well as IL2-dependent CTLL cell growth, were strongly inhibited in a dose-dependent manner when cells were preincubated in the presence of 5-10 microM D-PDMP, but not with its stereoisomer L-PDMP. Closely associated with this growth-inhibitory effect in the presence of D-PDMP, levels of essentially all GSLs, including GM3 and other gangliosides, were greatly reduced, whereas ceramide accumulated. Importantly, metabolically labeled radioactive bands, corresponding to free sphingosine and N-monomethylsphingosine, were found to be present in very small quantities (5-12%) relative to the band corresponding to N,N-dimethylsphingosine (DMS), which showed significant accumulation in D-PDMP-treated lymphocytes. The quantity of IL2 receptors and their affinity to IL2 on T cells did not change, but IL2-dependent tyrosine phosphorylation was greatly stimulated, following D-PDMP treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

A new cytokine receptor superfamily

The amino acid sequences of several, recently cloned cytokine receptors show significant homologies, primarily in their extracellular, ligand-binding domains. With one exception, their cognate cytokines mediate biological activities on a variety of hematopoietic cell types; thus we have designated the receptors as the hematopoietic receptor superfamily.

Monoclonal antibodies block murine IL-4 receptor function

IL-4 is a cytokine which can induce B-lymphocyte proliferation, increase cell-surface Ia expression, and induce some activated B cells to differentiate and begin to secrete IgE. IL-4 binds specifically to a cell-surface receptor (IL-4R) on cells from a variety of lineages including T and B cells. In general both primary cells and in vitro cell lines express less than 5000 receptors per cell. Utilizing a subclone of the cytotoxic T cell line CTLL-2 expressing a high level of IL-4R, mAb against the murine IL-4R were prepared. Two mAb have been identified which have different properties. These antibodies, designated M1 and M2, recognize sequences specific to the murine IL-4R. Immunoprecipitation studies with M1 and M2 on CTLL-2 cells have identified the receptor as a Mr = 145,000 cell-surface protein. Similar results have been obtained with the recently isolated full length murine IL-4R cDNA expressed in COS-7 cells. In addition the antibodies are capable of inhibiting IL-4 binding. One antibody, M1, is also a potent inhibitor of IL-4-induced proliferation. These antibodies will be useful in dissecting a wide array of activities attributed to IL-4.

Monoclonal antibodies block murine IL-4 receptor function

IL-4 is a cytokine which can induce B-lymphocyte proliferation, increase cell-surface Ia expression, and induce some activated B cells to differentiate and begin to secrete IgE. IL-4 binds specifically to a cell-surface receptor (IL-4R) on cells from a variety of lineages including T and B cells. In general both primary cells and in vitro cell lines express less than 5000 receptors per cell. Utilizing a subclone of the cytotoxic T cell line CTLL-2 expressing a high level of IL-4R, mAb against the murine IL-4R were prepared. Two mAb have been identified which have different properties. These antibodies, designated M1 and M2, recognize sequences specific to the murine IL-4R. Immunoprecipitation studies with M1 and M2 on CTLL-2 cells have identified the receptor as a Mr = 145,000 cell-surface protein. Similar results have been obtained with the recently isolated full length murine IL-4R cDNA expressed in COS-7 cells. In addition the antibodies are capable of inhibiting IL-4 binding. One antibody, M1, is also a potent inhibitor of IL-4-induced proliferation. These antibodies will be useful in dissecting a wide array of activities attributed to IL-4.