Isolation of LERK-5: a ligand of the eph-related receptor tyrosine kinases

Hek and elk are members of the eph-related family of receptor tyrosine kinases. Recently we isolated four cDNAs encoding membrane-bound ligands to hek and elk [Beckman et al. (1994) EMBO J. 13, 3757-3762; Kozlosky et al. (1995) Oncogene 10, 299-306]. Because of the promiscuous nature of their binding, we have termed these proteins ligands of the eph-related kinases or LERKs. A search of GenBank revealed an expressed sequence tag (EST) with homology to the LERKs. Using this EST as a probe, we have isolated human and murine cDNAs that encode a protein which we call LERK-5. The human and murine cDNAs encode proteins of 333 and 336 amino acids, respectively, with a 97% amino acid identity; LERK-5 has an amino acid identity of 27-59% with the other reported LERKs. LERK-5 is a ligand for both elk and hek and induces receptor phosphorylation. It is expressed in adult lung and kidney and the fetal tissues heart, lung, kidney, and brain. In addition, Southern blot analysis of DNA from interspecific backcross mice indicated that LERK-5 (Eplg5) maps to the proximal region of mouse chromosome 8.

Identification and cloning of a novel IL-15 binding protein that is structurally related to the alpha chain of the IL-2 receptor

Interleukin-15 (IL-15) is a novel cytokine of the four-helix bundle family which shares many biological activities with IL-2, probably due to its interaction with the IL-2 receptor beta and gamma (IL-2R beta and gamma c) chains. We report here the characterization and molecular cloning of a distinct murine IL-15R alpha chain. IL-15R alpha alone displays an affinity of binding for IL-15 equivalent to that of the heterotrimeric IL-2R for IL-2. A biologically functional heteromeric IL-15 receptor complex capable of mediating IL-15 responses was generated through reconstruction experiments in a murine myeloid cell line. IL-15R alpha is structurally similar to IL-2R alpha; together they define a new cytokine receptor family. The distribution of IL-15 and IL-15R alpha mRNA suggests that IL-15 may have biological activities distinct from IL-2.

IL-15, a novel T cell growth factor that shares activities and receptor components with IL-2

Interleukin 15 is a newly discovered cytokine that shares biological activities with IL-2 and, like IL-2, is a member of the four-helix bundle cytokine family. We have shown that IL-15 shares components of the receptor for IL-2: the alpha chain of the IL-2R is not required, but both the beta and gamma chains are needed for IL-15 mediated bioactivities. A defect in IL-15 signaling may therefore contribute to the phenotype of X-linked severe combined immunodeficiency in humans, resulting from mutations in the common gamma chain. Differential ability of cells to bind and respond to IL-2 and IL-15 suggested the existence of an additional IL-15 specific receptor component. We identified an IL-15 specific binding protein (IL-15R alpha) on a murine T cell and isolated the corresponding cDNA. The IL-15R alpha is not a member of the hematopoietin receptor superfamily, but is structurally related to the alpha chain of the IL-2R. Differences in the expression pattern of IL-15 and its receptor compared to the IL-2 system suggest unique in vivo roles for IL-15.

Conserved amino acids in the human granulocyte-macrophage colony-stimulating factor receptor-binding subunit essential for tyrosine phosphorylation and proliferation

A superfamily of growth factor and cytokine receptors has recently been identified, which is characterized by four spatially conserved cysteine residues and a tryptophan-serine motif (WSXWS) in the extracellular domain and proline-rich cytoplasmic domain. The high-affinity human granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor, hGM-CSFR, consists of two subunits, alpha (hGM-CSFR alpha), which is required for ligand binding, and beta (hGM-CSFR beta), which is required for signal transduction. Both the alpha and beta subunits are members of the cytokine receptor superfamily. In this study, we analyzed mutations in the conserved amino acids of the alpha subunit to determine their function in signal transduction, as assayed by tyrosine phosphorylation and proliferation. Disruption of either of the conserved disulfide bonds in the extracellular domain abolishes low-affinity binding but not binding to a preformed heterodimeric complex with the beta-chain. Cells expressing receptors with mutations in cysteines 2 or 3 grew as well as cells expressing wild-type receptors in human GM-CSF (hGM-CSF) and phosphorylated the same proteins on tyrosine residues, although the level of phosphorylation may be attenuated; cysteine 3 appears to be required for generation of the true high-affinity binding site. The WSXWS motif and the cytoplasmic domain are required for function of the human GM-CSF receptor, as stable cell lines expressing receptors with these mutations were unable to proliferate continuously in hGM-CSF. Surprisingly, no function for the conserved proline-rich region of the cytoplasmic domain could be ascertained from these studies; cells expressing these receptors were indistinguishable from wild-type in both binding and functional assays.

Conserved amino acids in the human granulocyte-macrophage colony-stimulating factor receptor-binding subunit essential for tyrosine phosphorylation and proliferation

A superfamily of growth factor and cytokine receptors has recently been identified, which is characterized by four spatially conserved cysteine residues and a tryptophan-serine motif (WSXWS) in the extracellular domain and proline-rich cytoplasmic domain. The high-affinity human granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor, hGM-CSFR, consists of two subunits, alpha (hGM-CSFR alpha), which is required for ligand binding, and beta (hGM-CSFR beta), which is required for signal transduction. Both the alpha and beta subunits are members of the cytokine receptor superfamily. In this study, we analyzed mutations in the conserved amino acids of the alpha subunit to determine their function in signal transduction, as assayed by tyrosine phosphorylation and proliferation. Disruption of either of the conserved disulfide bonds in the extracellular domain abolishes low-affinity binding but not binding to a preformed heterodimeric complex with the beta-chain. Cells expressing receptors with mutations in cysteines 2 or 3 grew as well as cells expressing wild-type receptors in human GM-CSF (hGM-CSF) and phosphorylated the same proteins on tyrosine residues, although the level of phosphorylation may be attenuated; cysteine 3 appears to be required for generation of the true high-affinity binding site. The WSXWS motif and the cytoplasmic domain are required for function of the human GM-CSF receptor, as stable cell lines expressing receptors with these mutations were unable to proliferate continuously in hGM-CSF. Surprisingly, no function for the conserved proline-rich region of the cytoplasmic domain could be ascertained from these studies; cells expressing these receptors were indistinguishable from wild-type in both binding and functional assays.

Early lymphocyte expansion is severely impaired in interleukin 7 receptor-deficient mice

Interleukin 7 (IL-7) stimulates the proliferation of B cell progenitors, thymocytes, and mature T cells through an interaction with a high affinity receptor (IL-7R) belonging to the hematopoietin receptor superfamily. We have further addressed the role of IL-7 and its receptor during B and T cell development by generating mice genetically deficient in IL-7R. Mutant mice display a profound reduction in thymic and peripheral lymphoid cellularity. Analyses of lymphoid progenitor populations in IL-7R-deficient mice define precisely those developmental stages affected by the mutation and reveal a critical role for IL-7R during early lymphoid development. Significantly, these studies indicate that the phase of thymocyte expansion occurring before the onset of T cell receptor gene rearrangement is critically dependent upon, and mediated by the high affinity receptor for IL-7.

Utilization of the beta and gamma chains of the IL-2 receptor by the novel cytokine IL-15

We have recently cloned a novel cytokine, IL-15, with shared bioactivities but no sequence homology with IL-2. We found high affinity IL-15 binding to many cell types, including cells of non-lymphoid origin. Analysis of IL-15 interaction with subunits of the IL-2 receptor (IL-2R) revealed that the alpha subunit was not involved in IL-15 binding. We demonstrated directly in cells transfected with IL-2R subunits that both the beta and gamma chains are required for IL-15 binding and signaling. Hence, IL-15, like IL-2, IL-4 and IL-7, utilizes the common IL-2R gamma subunit found to be defective in X-linked severe combined immunodeficiency in humans. IL-15 is the only cytokine other than IL-2 that has also been shown to share the beta signaling subunit of IL-2R. The differential ability of some cells to bind and respond to IL-2 and IL-15 implies the existence of an additional IL-15-specific component.

Identification of conserved amino acids in the human granulocyte-macrophage colony-stimulating factor receptor alpha subunit critical for function. Evidence for formation of a heterodimeric receptor complex prior to ligand binding

A superfamily of growth factor and cytokine receptors has recently been identified, which is characterized by four spatially conserved cysteine residues, a tryptophan-serine motif (WSXWS) in the extracellular domain, and a proline-rich cytoplasmic domain. The high affinity human granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor (hGM-CSFR) consists of two subunits, alpha (hGM-CSFR alpha) and beta (hGM-CSFR beta), both of which are members of the receptor superfamily. In this study, we prepared mutations in conserved amino acids of the receptor subunit necessary for GM-CSF binding (hGM-CSFR alpha) and analyzed mutant receptors for low affinity binding, internalization, and high affinity binding when complexed with the beta subunit. Mutations in the cytoplasmic domain did not affect GM-CSF binding or receptor internalization. Mutation of a single conserved serine residue within the WSXWS motif diminishes cell surface receptor expression but not ligand binding. Mutation of either the second or third conserved cysteine residue of hGM-CSFR alpha resulted in complete loss of low affinity binding; however, co-expression of the cysteine 2 mutant with hGM-CSFR beta yielded a high affinity receptor complex. Since neither the cysteine 2 mutant nor the beta subunit can bind ligand alone, this result suggests that hGM-CSFR alpha and hGM-CSFR beta exist in a preformed heterodimeric protein complex on the plasma membrane.

The human pseudoautosomal GM-CSF receptor alpha subunit gene is autosomal in mouse

The gene encoding the granulocyte macrophage colony stimulating factor receptor alpha subunit (CSF2RA) has previously been mapped to the pseudoautosomal region of the human sex chromosomes. In contrast, we report that the murine locus, Csf2ra, maps to an autosome in the laboratory mouse. By in situ hybridization and genetic mapping, Csf2ra maps at telomeric band D2 of mouse chromosome 19. This first instance of a pseudoautosomal locus in human being autosomal in mouse, indicates incomplete conservation between the human and mouse X chromosomes and suggests that the genetic content of the pseudoautosomal region may differ between species of eutherian mammals due to chromosomal rearrangements.

Dissociation of human cytokine receptor expression and signal transduction

We have examined the relationship between granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3) receptor expression and signal transduction in populations of HL-60 cells differing in proliferative capacity to these cytokines. GM-CSF or IL-3 stimulation of HL-60 cells pretreated with either dimethyl sulfoxide (DMSO) or retinoic acid results in increases in proliferative response as well as both tyrosine and serine phosphorylation. In contrast, neither GM-CSF or IL-3 stimulation of parental HL-60 cells (those not treated with DMSO or retinoic acid) produced any changes in either proliferation or protein phosphorylation. Thus, although parental HL-60 cells expressed both GM-CSF and IL-3 receptors, treatment with either DMSO or retinoic acid was necessary to confer the capacity for signal transduction as assessed by both a biologic and biochemical response. Pretreatment of cells with genistein, a protein tyrosine kinase inhibitor, resulted in inhibition of GM-CSF-induced protein tyrosine phosphorylation as well as proliferation. These data show a strong correlation between cytokine-induced increases in protein phosphorylation and subsequent biologic responses. Further, this work demonstrates that cytokine receptor expression and signal transduction can be disassociated and suggests the potential for independent regulation of these two components of signal transduction.

Human GM-CSF receptor alpha-chain gene is highly polymorphic but not rearranged in AML

Acute myeloid leukaemia (AML) blast cells express haemopoietic growth factor receptors. However, their presence does not predict response to the cognate ligand in vitro. This suggests that haemopoietic growth factor receptor structure or function may be abnormal in some cases of acute myeloid leukaemia. The granulocyte-macrophage colony-stimulating factor receptor alpha-chain gene (GM-CSF-R) has recently been localised to the pseudoautosomal region of the sex chromosomes. A sex chromosome is lost in 25% of cases of AML FAB subtype M2. The loss of one allele of this gene may have some aetiological significance in AML if the other allele is altered leading to abnormal receptor structure, function or number. In this initial study, we have examined DNA from leukaemic cells of 29 patients with AML, including three with FAB subtype M2 with deletion of an X or Y chromosome for evidence of gross rearrangement of this gene. We report that although the gene is highly polymorphic for a number of restriction enzymes, we have found no evidence of gross rearrangement in AML.

The interleukin-7 receptor gene is at 5p13

A DNA probe for the interleukin-7 receptor gene was used for in situ hybridisation and Southern blot analysis of a series of rodent-human hybrid cell lines. The IL-7 receptor gene maps to 5p13.

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.