Recombinant human interleukin 5 is an eosinophil differentiation factor but has no activity in standard human B cell growth factor assays

Binding interactions of human interleukin 5 with its receptor alpha subunit. Large scale production, structural, and functional studies of Drosophila-expressed recombinant proteins

Human interleukin 5 (hIL5) and soluble forms of its receptor alpha subunit were expressed in Drosophila cells and purified to homogeneity, allowing a detailed structural and functional analysis. B cell proliferation confirmed that the hIL5 was biologically active. Deglycosylated hIL5 remained active, while similarly deglycosylated receptor alpha subunit lost activity. The crystal structure of the deglycosylated hIL5 was determined to 2.6-A resolution and found to be similar to that of the protein produced in Escherichia coli. Human IL5 was shown by analytical ultracentrifugation to form a 1:1 complex with the soluble domain of the hIL5 receptor alpha subunit (shIL5R alpha). Additionally, the relative abundance of ligand and receptor in the hIL5.shIL5R alpha complex was determined to be 1:1 by both titration calorimetry and SDS-polyacrylamide gel electrophoresis analysis of dissolved cocrystals of the complex. Titration microcalorimetry yielded equilibrium dissociation constants of 3.1 and 2.0 nM, respectively, for the binding of hIL5 to shIL5R alpha and to a chimeric form of the receptor containing shIL5R alpha fused to the immunoglobulin Fc domain (shIL5R alpha-Fc). Analysis of the binding thermodynamics of IL5 and its soluble receptor indicates that conformational changes are coupled to the binding reaction. Kinetic analysis using surface plasmon resonance yielded data consistent with the Kd values from calorimetry and also with the possibility of conformational isomerization in the interaction of hIL5 with the receptor alpha subunit. Using a radioligand binding assay, the affinity of hIL5 with full-length hIL5R alpha in Drosophila membranes was found to be 6 nM, in accord with the affinities measured for the soluble receptor forms. Hence, most of the binding energy of the alpha receptor is supplied by the soluble domain. Taken with other aspects of hIL5 structure and biological activity, the data obtained allow a prediction for how 1:1 stoichiometry and conformational change can lead to the formation of hIL5.receptor alpha beta complex and signal transduction.

Interleukin 5 expressing allergen-specific T-lymphocytes in patients with house dust mite sensitization: analysis at a clonal level

Interleukin 5 (IL-5) is a T-cell lymphokine known to stimulate development, functional activity, and in vitro survival of eosinophils. Tissue and blood eosinophilia occurring during allergic responses of the immune system are potentially mediated by IL-5 secreting T-cells. To test this hypothesis a series of allergen-specific T-cell clones were established from peripheral blood and skin lymphocytes of patients with atopic dermatitis and house dust mite sensitization. In addition, alloreactive T-cell clones were also prepared from peripheral blood lymphocytes of healthy donors. Cloned T-cells were analyzed for IL-5 mRNA expression and IL-5 secretion by means of in vitro gene amplification using the reverse transcriptase polymerase chain reaction and IL-5 specific oligonucleotide hybridization, as well as IL-5-specific ELISA. A majority of allergen-specific long-term cultured T-cell clones (84%) of different donors and of either phenotype (CD8+ or CD4+) disclosed IL-5 transcripts on stimulation with lectins. Almost all clones exhibiting IL-5 transcripts also released immunoreactive IL-5 protein into their culture supernatants. In contrast, only 2% of alloreactive T-cell clones obtained from healthy donors and none of alloreactive T-cell clones of one atopic patient investigated expressed detectable amounts of IL-5 mRNA in response to lectin stimulation, all of whom were CD4+. These results suggest that eosinophilia observed in allergic responses in the peripheral blood and in tissues at the site of induced late-phase cutaneous reaction may be associated with IL-5 release by allergen-specific T-cells.

Identification and characterization of a functional promoter region in the human eosinophil IL-5 receptor alpha subunit gene

The molecular basis for the commitment of multipotential myeloid progenitors to the eosinophil lineage, and the transcriptional mechanisms by which eosinophil-specific genes are subsequently expressed and regulated during eosinophil development are currently unknown. Interleukin-5 (IL-5) is a T cell and mast cell-derived cytokine with actions restricted to the eosinophil and closely related basophil lineages in humans. The high affinity receptor for IL-5 (IL-5R) is composed of an alpha subunit (IL-5R alpha) expressed by the eosinophil lineage, that associates with a beta c subunit shared with the receptors for IL-3 and granulocyte-macrophage colony stimulating factor (GM-CSF). As a prerequisite to studies of the transcriptional regulation of the IL-5R alpha subunit gene, we used three different methods, including primer extension, RNase protection, and 5'-RACE to precisely map the transcriptional start site to a position 15 base pairs (bp) upstream of the 5' end of the published sequence of IL-5R alpha exon 1. To initially identify the IL-5R alpha promoter, 3.5 kilobases (kb) and 561 bp of the 5' sequence flanking the transcriptional start site were subcloned into the promoterless pXP2-luciferase vector. Transient transfection of these constructs into an eosinophil-committed HL-60 subline, clone HL-60-C15, induced the expression of approximately 240-fold greater luciferase activity than the promoterless vector, identifying a strong functionally active promoter region within the 561 bp of sequence proximal to the transcriptional start site and with activity equivalent to pXP2 constructs containing the entire 3.5 kb of upstream sequence. To more precisely localize the cis-acting regulatory elements in this region important for promoter activity, a series of 5' deletion mutants of the 561-bp region were generated in the pXP2-luciferase vector. Deletion of the region between bp -432 and -398 reduced promoter activity by more than 80% in the HL-60-C15 cell line. Further analyses of the activity of the IL-5R alpha promoter constructs in various other eosinophil, myeloid, and non-myeloid cell lines indicated that the promoter was relatively myeloid and eosinophil lineage-specific in its expression. Consensus sequences for known transcription factor binding sites were not present in the 34-bp region of the promoter required for maximal activity, suggesting unique myeloid- and possibly eosinophil-specific regulatory elements.(ABSTRACT TRUNCATED AT 400 WORDS)

Kinetic characterization of the interaction of biotinylated human interleukin 5 with an Fc chimera of its receptor alpha subunit and development of an ELISA screening assay using real-time interaction biosensor analysis

The interaction of biotinylated human interleukin 5 ([BT]hIL5) with immobilized receptor was measured with a real-time biosensor, and these results were used as a basis for configuring an ELISA for screening antagonists of hIL5-receptor binding. The recombinant proteins used, hIL5 and shIL5R alpha-Fc (chimeric fusion receptor constructed by linking the soluble component of the hIL5 receptor alpha subunit to the constant domain (Fc) of immunoglobulin G), were produced by the expression of cloned vectors in Drosophila schneider (S2) cells. Initial attempts to develop a screening assay by direct immobilization of soluble IL5 receptor to microtiter plates proved unsatisfactory and led to use of the Fc chimera attached by oriented immobilization via protein A. Hence, shIL5R alpha-Fc was bound to protein A covalently immobilized on a carboxymethyl dextran (CM-5) biosensor chip. Specific binding was demonstrated of [BT]hIL5 to protein A/shIL5R alpha-Fc receptor complex. The binding was high affinity (Kdapp = 6 nM), reversible and saturable. The affinity of [BT]hIL5 was similar to that determined with the biosensor assay for unmodified hIL5. The observed kinetics of the interactions of Fc chimera with protein A (slow dissociation) and of [BT]hIL5 with immobilized Fc chimera (faster dissociation) were favorable for subsequently establishing a microtiter plate based ELISA assay. In the latter, Fc chimera was immobilized to the plate via protein A as in the biosensor experiment. Binding of [BT]hIL5 to immobilized Fc chimera in the ELISA was concentration dependent and was competed by both hIL5 and shIL5R alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced detection of human IL-5 in biological fluids utilizing murine monoclonal antibodies which delineate distinct neutralizing epitopes

Interleukin 5 (IL-5) is a homodimeric cytokine arranged in a head-to-tail configuration covalently linked by two disulfide bonds. IL-5 has pleiotropic effects on murine and human leukocytes and has been implicated in the pathogenesis of many inflammatory disorders. To facilitate the study of functionally relevant IL-5 domains involved in receptor binding and to develop a highly sensitive and specific ELISA capable of detecting IL-5 in biological fluids, a library of murine anti-human IL-5 (hIL-5) mAb was generated to baculovirus expressed recombinant hIL-5 (rhIL-5). Fifteen subclones of seven hybridomas were characterized. All mAb bound hIL-5, but not murine IL-5 (mIL-5), and neutralized hIL-5 biological activity in the BCl1 proliferation assay. By competitive ELISA, the mAb were divided into two binding groups. Utilizing comparative analysis with TRFK-5, a rat anti-mIL-5 mAb crossreactive with hIL-5, at least three hIL-5 neutralizing epitopes were defined. By ELISA and Western analysis, each epitope was shown to be present as a conformationally identical pair on the hIL-5 dimer. Various combinations of mAb in sandwich ELISA were used to predict the relative proximity of each epitope pair. Utilizing mAb binding characteristics, highly sensitive and specific sandwich ELISA were developed with a minimum detection limit of 6.25 pg hIL-5/ml (P < 0.05). Quantitation of hIL-5 in both serum and bronchoalveolar lavage (BAL) fluid demonstrated the utility of these anti-hIL-5 mAb for investigating the role of hIL-5 in inflammation. These mAb should also serve as useful reagents for epitope mapping of functional hIL-5 domains.

The potential role of cytokines in the pathogenesis of Epstein-Barr virus associated post-transplant lymphoproliferative disease

Post-transplant lymphoproliferative disease (PTLD) is a complication of Epstein-Barr virus infection occurring in immunosuppressed transplant recipients. Non-clonal lesions with a polymorphous histology have the potential of regressing, if the degree of immunosuppression is reduced, thereby giving the immune system a chance to recuperate. In contrast, clonal tumors with a monomorphous histology portend a bad clinical outcome. This review summarizes evidence that the biological behavior of PTLD may be predicated on intercellular interactions involving multiple cytokines. With further investigations to clarify the nature of these interactions, it should be possible to design rational strategies for the cytokine therapy of human PTLD.

Analysis of the interaction between human interleukin-5 and the soluble domain of its receptor using a surface plasmon resonance biosensor

A surface plasmon resonance (SPR) biosensor was used to study the interaction of human interleukin-5 (hIL5) with its receptor. IL5 is a major growth factor in the production and activation of eosinophils. The receptor for IL5 is composed of two subunits, alpha and beta. The alpha subunit provides the specificity for IL5 and consists of an extracellular soluble domain, a single transmembrane region and a cytoplasmic tail. We expressed the soluble domain of the human IL5 receptor alpha subunit (shIL5R alpha) and human IL5 (hIL5) in Drosophila. Both hIL5 and shIL5R alpha were immobilized separately through amine groups onto the carboxylated dextran layer of sensor chips of the BIAcore (Pharmacia) SPR biosensor after N-hydroxysuccinimide/carbodiimide activation of the chip surface. Interactions were measured for the complementary macromolecule, either shIL5R alpha or hIL5, in solution. Kinetics of binding of soluble analyte to immobilized ligand were measured and from this the association rate constant, dissociation rate constant and equilibrium dissociation constant (Kd) were derived. With immobilized shIL5R alpha and soluble hIL5, the measured Kd was 2 nM. A similar value was obtained by titration calorimetry. The Kd for Drosophila expressed receptor and IL5 is higher than the values reported for proteins expressed in different systems, likely due to differences in the methods of interaction analysis used or differences in protein glycosylation. Receptor-IL5 binding was relatively pH independent between pH 6.5 and 9.5. Outside this range, the dissociation rate increased with comparatively little increase in association rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal response to IL-5 in B-cell chronic lymphocytic leukemia

In B-cell chronic lymphocytic leukemia, neoplastic B-lymphocytes are arrested in development. Since interleukins are essential for B-cell differentiation, we examined whether B-CLL cells were capable of responding normally to interleukins. Purified B-lymphocytes from B-CLL patients and controls were compared for their ability to proliferate and differentiate after stimulation with MCAT or SAC plus rhIL-2 or rhIL-5. When rhIL-5 was added to MCAT-stimulated cells, 8 of 10 controls showed a substantial increase in IgM production, compared with only 1 of 10 B-CLL patients. Lack of IL-5 responsiveness could provide insight into the arrested B-lymphocyte development of some B-CLL patients.

Human interleukin-5 induces staphylococcal A Cowan 1 strain-activated human B cells to secrete IgM

Studies on the role of human interleukin (IL)-5 in B cell growth and differentiation have yielded conflicting results. To clarify this issue, we studied the role of purified recombinant IL-5 on activated human B cells which were depleted of T cells and adherent cells. Human IL-5 augments IgM secretion, but not IgG or IgA secretion of purified human B cells activated with staphylococcal A Cowan 1 strain (SAC). However, the period of B cell activation with SAC is critical for the B cell to respond to IL-5. After 24 h of SAC activation, human B cells are responsive to the IL-5 signal, but with longer periods of activation, IL-5 responsiveness diminishes. This may explain some of the previous conflicting results. The IgM enhancement was not seen when B cells were activated with pokeweed mitogen. In addition, human recombinant IL-4 synergized with IL-5 in augmenting IgM secretion by SAC-activated B cells, while IL-5 synergized with IL-2 to augment IgM, IgG and IgA secretion by SAC-activated B cells. As the purified IL-5 was derived from a COS-1 cell supernatant, and COS-1 cells secrete IL-6, we examined whether a polyclonal IL-6 antibody blocked the IgM-enhancing activity of IL-5. IL-6 antibody did not block the IL-5 enhancement of IgM secretion, but a monoclonal antibody to IL-5 inhibited the human IL-5 activity on human B cells. These results demonstrate that human IL-5 augments IgM secretion of SAC-activated human B-cells. In addition, this lymphokine synergizes with IL-4 and IL-2 in supporting Ig secretion.

The biology of interleukin-5 and its receptor

IL-5 is primarily a T-cell-derived cytokine that has multiple regulatory functions on eosinophils and (in the mouse) on antibody-secreting B cells. A complex network of cytokines appear to control transcription of the gene for IL-5 and its production. Abnormally high levels of this cytokine are associated with infections with tissue-dwelling parasites and a diverse group of hypereosinophilic conditions of no known etiology. Our understanding of the biological role of IL-5 in the regulation of Ig production and the development of immunity to parasites is far from complete, but basic knowledge of its action at the cellular level is accumulating and will be critical for the intelligent application of immunotherapy with IL-5 or antibodies to IL-5 in infectious, neoplastic, and possibly other diseases.

Proliferation of the BCL1 B cell lymphoma induced by IL-4 and IL-5 is dependent on IL-6 and GM-CSF

Lymphokine requirements for the in vitro proliferation of the spleen-dependent B cell lymphoma BCL1 have been analysed. Cells were found to respond by proliferation to added recombinant (r) interleukin-4 (IL-4), r-IL-5 and recombinant granulocyte-macrophage colony-stimulating factor (r-GM-CSF). Inhibition by antibodies specific for each of these lymphokines has confirmed growth factor-dependent growth. Anti-GM-CSF has, however, been found to inhibit the proliferation of BCL1 cells induced by r-IL-4 and r-IL-5, as well as r-GM-CSF, suggesting that BCL1 cells may express receptors for GM-CSF and that GM-CSF may be able to act synergistically with IL-4 and IL-5 in promoting cell proliferation. Anti-IL-6 antibody was also found to be a very effective inhibitor of BCL1 proliferation induced by either IL-4 or IL-5 but not by GM-CSF. Added IL-6 did not stimulate BCL1 proliferation, suggesting that endogenous IL-6 may regulate the autocrine growth of BCL1 cells. BCL1 cell proliferation in vitro appears to be regulated by interactions between multiple growth factors.

Human interleukin-5 expressed in Escherichia coli has N-terminal modifications

Recombinant human interleukin-5 exists as four major isoforms all possessing N-terminal methionine. Peptide mapping and subsequent analysis by fast-atom-bombardment mass spectrometry (f.a.b.-m.s.) have shown that N-terminal modifications are the cause of the charge heterogeneity. In order of decreasing abundance, these are unmodified methionine, retention of N-terminal formyl group, oxidation of N-terminal methionine to sulphoxide and carbamoylation of the N-terminus. These results were confirmed by analysis of the reduced and alkylated intact protein by electrospray-ionization mass spectrometry. The implications of these findings for the production and characterization of recombinant proteins are briefly discussed.

Effects of IL-4, IL-5, and IL-6 on growth and immunoglobulin production of Epstein-Barr virus-infected human B cells

In the present study we investigated whether interleukin-4 (IL-4), IL-5, and IL-6 could enhance the efficiency of Epstein-Barr virus (EBV) transformation for the generation of specific human monoclonal antibody (HuMAb)-producing B-cell lines directed against erythrocyte Rhesus(D) antigen. In newly EBV-infected B cells, IL-4 and IL-6 caused a comparable enhancement of proliferation and of total IgG and IgA production. IL-6 showed a much stronger effect than IL-4 on IgM production, whereas IL-4 was unique in inducing IgE production. No stimulatory effects of IL-5 on either growth or Ig production were observed. Although addition of IL-6 resulted during the early phase after EBV infection in high numbers of Ag-specific antibody-producing wells, this did not result in an increased number of stable HuMAb-secreting cell lines. When the effects of cytokines were tested on established polyclonal EBV B cells, in a high cell density culture system, only IL-6 was able to enhance Ig secretion, while no effect could be demonstrated on proliferation. These studies substantiate that IL-6 is an important regulator of proliferation and Ig production, and that it acts at distinct stages after EBV infection, but does not increase the final overall recovery of Ag-specific EBV B-cell lines.

The cytokine network in the critically ill

There is increasing experimental and clinical evidence that a number of cytokines play a major role in the response to injury and infection and in the development of organ damage in critically ill patients. Tumour necrosis factor (TNF) is now proposed to be a key mediator of organ injury during sepsis. It is elevated early in the course of septic shock and high levels correlate with unfavourable outcome. In animals it can produce the effects of endotoxin. The prophylactic administration of anti-TNF antisera protects mice and rabbits from lethal effects of lipopolysaccharide. Interleukin-1 (IL-1) is an endogenous pyrogen which induces leukocytosis and muscle catabolism. It causes hypotension and tachycardia by reducing smooth muscle contractility. IL-1 receptor blockers have been shown to diminish mortality in experimental endotoxic shock. Interleukin-6 (IL-6) is a pyrogen and lymphocyte activator. It is the major stimulus to acute phase protein production by the liver. A recently described neutrophil-activating peptide (Interleukin-8; IL-8) may be involved in the pathogenesis of ARDS. High blood levels of IL-8 have been found in patients with septic shock. Platelet-derived growth factor (PDGF) has been shown to stimulate TNF production, leukocyte chemotaxis and pulmonary vasoconstriction in response to endotoxin. Other cytokines and growth factors have not yet been studied in critical illness. The cytokine network can be either protective or damaging. Its activation during critical illness triggers complex and still poorly understood interactions. A better comprehension of its role in protection from infection and in the pathogenesis of multiple organ failure may allow therapeutic manipulations aimed at minimising adverse effects while retaining immunological protection.

IL-5 responsive subsets among normal and lymphomatous murine B cells

Two normal murine B-cell subpopulations, germinal center and coelomic B cells, and at least some of the lymphomas derived from them, respond to IL-5. In the case of normal B cells, a comitogen (DxS) is required. IFN-gamma is strongly inhibitory to proliferation of the coelomic B-cell subset but not for germinal center cells or the SJL lymphomas derived from them.

Possible Role of Cytokines in the Pathogenesis of Non-Organ Specific Autoimmunity

This paper describes the experiments conducted in our laboratory on the mode of activation of CD5 + B cells. The data show that these cells are stimulated in a manner that is less dependent of T cell help as compared to CD5- cells and define IL-2 as the major growth and differentiation factor for CD5 + cells. These data are discussed in the light of the supposed function of CD5 + cells that seem represented by the capacity to release polyspecific antibodies reacting with a multiplicity of antigens from various pathogens. These antibodies, also called natural antibodies, probably represent one of the first line of defense against invading microrganisms.

Functional properties of human germinal center B cells

Germinal centers (GCs) are histologically defined areas where B cells undergo extensive proliferation and maturation, or die of apoptosis. GC B cells isolated from human tonsils can be phenotypically identified by expression of peanut agglutinin (PNA)-binding sites and can be further divided into subpopulations based on their expression of CD77. To assess the functional potential of GC B cells, we studied CD77+ PNA+ B cells isolated from tonsils by examining their differentiation status and their ability to proliferate in vitro to various cytokines and costimulants. We found that CD77+ GC B cells are less differentiated than CD77- GC B cells; GC B cells less frequently express cytoplasmic IgG and IgM, and spontaneously secrete less Ig compared to CD77- GC B cells. To identify conditions capable of inducing GC B cell proliferation, we examined IL-4, IL-2, IFN-gamma, low molecular weight BCGF (LMW-BCGF), and an MLR supernatant along with costimulants such as anti-IgM antibody, Staphylococcus aureus Cowan I (SAC), PMA, and pokeweed mitogen (PWM). While non-GC B cells proliferate strongly in response to these stimuli, GC B cells did not proliferate. However, CD77+ as well as CD77- GC B cells mounted a rapid and strong proliferative response upon stimulation with IL-4, but only in the presence of anti-CD40 antibody. Moreover, although nine additional cytokines were examined, only IL-4 was capable of supporting CD77+ GC B cell proliferation in the presence of anti-CD40 antibody. When cells were stimulated with IL-4 and anti-CD40 antibody, we also found that IFN-gamma consistently decreased the proliferative response of CD77+ GC B cells without affecting the response of non-GC B cells. Taken together, these data indicate that GC B cells have characteristic growth requirements and that IL-4 may be important for GC B cell growth in vivo.

Effects of interleukin-5 on acute myeloid leukemias

Because of the known activity of interleukin-5 (IL-5) as a growth factor for human eosinophils, we performed studies to ascertain whether M4Eo acute leukemia cells might be capable of responding to IL-5. Surprisingly, short term incubation of freshly isolated M4Eo blasts with rhIL-5 induced differentiation of the cells to macrophages. To determine whether other variants of acute myelogenous leukemia (AML) might also be capable of responding to IL-5, we studied cells from four additional unselected cases and found that one responded to IL-5 by vigorous proliferation. Using biotinylated rhIL-5, second labelling with streptavidin-fluorescein isothiocyanate (FITC) and flow cytometric analysis, specific binding of IL-5 to both responsive leukemias was demonstrated, suggesting the presence of specific IL-5 receptors. Additional study will be needed to assess the frequency of IL-5 responsiveness in AML and to determine the relationship of these phenomena to the physiologic role of IL-5 in the regulation of hematopoiesis.

Molecular cloning and expression of the human interleukin 5 receptor

Human interleukin 5 (IL-5) plays an important role in proliferation and differentiation of human eosinophils. We report the isolation of cDNA clones from cDNA libraries of human eosinophils by using murine IL-5 receptor alpha chain cDNA as a probe. Analysis of the predicted amino acid sequence indicated that the human IL-5 receptor has approximately 70% amino acid sequence homology with the murine IL-5 receptor and retains features common to the cytokine receptor superfamily. One cDNA clone encodes a glycoprotein of 420 amino acids (Mr 47,670) with an NH2-terminal hydrophobic region (20 amino acids), a glycosylated extracellular domain (324 amino acids), a transmembrane domain (21 amino acids), and a cytoplasmic domain (55 amino acids). Another cDNA encodes only the extracellular domain of this receptor molecule. Other cDNA clones encode molecules having diversified cytoplasmic domains. COS7 cells transfected with the cDNA expressed a approximately 60-kD protein and bound IL-5 with a single class of affinity (Kd = 250-590 pM). The Kd values were similar to that observed in normal human eosinophils. In contrast to the murine 60-kD alpha chain, which binds IL-5 with low affinity (Kd = approximately 10 nM), the human alpha chain homologue can bind IL-5 with much higher affinity by itself. RNA blot analysis of human cells demonstrated two transcripts (approximately 5.3 and 1.4 kb). Both of them were expressed in normal human eosinophils and in erythroleukemic cell line TF-1, which responds to IL-5. The human IL-5 receptor characterized in this paper is essential for signal transduction, because expression of this molecule in murine IL-3-dependent cell line FDC-P1 allowed these cells to proliferate in response to IL-5.

Expression of interleukin 5 by the CD4+CD45R0+ subset of human T cells

The expression of IL5 by CD4+CD45RA+, CD4+CD45R0+ and CD3+CD8+ subsets of human peripheral blood mononuclear cells was assessed. Interleukin 5 expression was detected by RNA extraction, reverse transcription and polymerase chain reaction. Populations of highly purified cells were obtained by a protocol of sequential plastic adherence, magnetic bead separation and flow cytometric cell sorting. IL5 was clearly expressed in the CD4+CD45R0+ subset from 3 to 48 hr after activation. The CD4+CD45RA+ and CD3+CD8+ subsets expressed very much less IL5. By contrast, IL2 expression was readily detected in all sorted populations. Thus, in activated CD4+ cells, IL5 was predominantly expressed in the CD4+CD45R0+ subset, a pattern of expression corresponding to that reported for a number of other cytokines, and differing from that of IL2.

Interleukin 5 messenger RNA expression by eosinophils in the intestinal mucosa of patients with coeliac disease

Interleukin 5 (IL-5), the major factor involved in eosinophil differentiation, is produced by T cells or mast cells. In the present study, we found that eosinophils infiltrating the mucosa of four patients with active coeliac disease also express the IL-5 mRNA. No positive signal was obtained in normal duodenum tissues and in the cell infiltrate from patients submitted to gluten restriction. The identification of labeled mucosal cells as eosinophils relied on their typical morphology. Moreover, highly purified blood eosinophils from three out of four patients with eosinophilia were also strongly labeled with the IL-5 antisense but not with the corresponding sense probe. Together, these results suggest that eosinophils have the capacity to synthesize IL-5, which could contribute to paracrine interactions with T and B cells and, in autocrine fashion, locally participate, through binding to the IL-5 receptor, to eosinophil differentiation and activation. These data might have implications not only in the pathology of coeliac disease but also in other diseases associated with eosinophil infiltration.

The effect of specific immunization or infection with Trichostrongylus colubriformis on production of eosinophil differentiation factors in guinea pigs

The cultivation of bone marrow was used to quantitate the levels of eosinophil differentiation factors (EDF) produced in conditioned medium (CM) by incubation of mesenteric lymph node cells (MLNC) with mitogens or specific antigens from the intestinal nematode parasite, Trichostrongylus colubriformis. In liquid cultures with 20 units ml-1 recombinant murine interleukin-5 (IL-5), bone marrow cells (BMC) from either normal or infected donors contained less than 5% eosinophils and differentiated to greater than 50% eosinophils over 2-3 weeks. Conditioned medium from 3-4 week infected donors produced between 20 and 50% eosinophils when donor MLNC were stimulated with the specific antigen preparation SP3, but macrophages predominated when using CM from MLNC incubated with Concanavalin A (ConA). CM from MLNC of challenged donors incubated with SP3 produced 30-70% eosinophils in BMC assays, with highest levels induced by CM from high responder (HR) donors. Marrow from parasitized or normal donors gave rise to comparable proportions of eosinophils. CM was also produced from LNC of donors given protein or parasite antigens in adjuvant where between 28 and 35% eosinophils were produced in culture. There were no differences between activities attributable to the antigen, but Freund's complete adjuvant induced earlier differentiation of BMC than alum-induced CM. The results confirm that high levels of EDF activity are specifically induced by parasitic infection, and can also be produced by intraperitoneal and subcutaneous inoculation of adjuvanted antigens. Consistent with the greater eosinophilia exhibited by HR guinea pigs to infection with T.colubriformis L3, their MLNC also produced the highest levels of EDF activity.

Interleukin 5 up-regulates high-affinity interleukin 2 receptor expression by human resting peripheral T cells: a comparison with the effect of interleukin 4 on B cells

The separate regulation mechanisms of cytokines on two classes of interleukin 2 receptors (IL-2R) on human peripheral T and B cells were analyzed by a flow cytometer using a double stain with IL-2R alpha (55 kilodalton Tac) and IL-2R beta (75 kilodalton mik beta 1, mik beta 3). Although the expression of IL-2R alpha by T cells was slightly enhanced by IL-2 and IL-4, expression of the beta chain was diminished by both cytokines. IL-5 by itself did not alter the expression of either IL-2R alpha or beta, but preculturing with IL-2 for 24 h followed by IL-5 for another 24 h induced an increase in IL-2R alpha expression and in simultaneous alpha/beta chain expression. Increased numbers of high-affinity IL-2R were confirmed by 125I binding assays. On B cells, IL-4 increased alpha, beta, and simultaneous alpha/beta chain expression, but IL-4-treated B cells did not show an increased number of high-affinity IL-2R.

There is no correlation between function and lymphokine production of HBs-antigen-specific human CD4(+)-cloned T cells

The question whether antigen-specific human CD4+ T cells can be classified on the basis of appropriate and fixed lymphokine production patterns and their corresponding functions still remains to be elucidated. We generated ten CD4+ T-cell clones specific for HBsAg from HBsAb-positive but HBsAg-negative individuals. Seven of these clones exhibited helper activity for HBsAb response, while the three other clones did not. Both helper- and non-helper-type T-cell clones produced interleukin 4 (IL-4) after antigenic stimulation. By stimulation with phytohaemagglutinin (PHA) plus phorbol myristate acetate (PMA), three of the seven helper-type clones produced interleukin 2 (IL-2) in addition to IL-4. However, the other four helper-type clones did not produce IL-2 by such stimulation, although they continued the production of IL-4. All non-helper-type T-cell clones produced a large amount of IL-2, and some of them completely became an IL-2 producer after certain stimulation. These results suggested that both helper- and non-helper-type CD4+ T-cell clones specific for HBsAg might have no strict pattern of lymphokine production as in the TH1/TH2 dichotomy of murine CD4+ T cells. The data also revealed that lymphokine-producing capacity of individual cloned T cells is changeable depending upon the sort of activation.

A human high affinity interleukin-5 receptor (IL5R) is composed of an IL5-specific alpha chain and a beta chain shared with the receptor for GM-CSF

cDNA clones encoding two receptor proteins involved in the binding of human interleukin 5 (hIL5) have been isolated. A first class codes for an IL5-specific chain (hIL5R alpha). The major transcript of this receptor gene, as analyzed in both HL-60 eosinophilic cells and eosinophilic myelocytes grown from cord blood, encodes a secreted form of this receptor. This soluble hIL5R alpha has antagonistic properties. A second component of the hIL5R is found to be identical to the beta chain of the human granulocyte-macrophage colony-stimulating factor (GM-CSF) high affinity receptor. The finding that IL5 and GM-CSF share a receptor subunit provides a molecular basis for the observation that these cytokines can partially interfere with each other's binding and have highly overlapping biological activities on eosinophils.

Effect of recombinant interleukin 5 on the generation of cytotoxic T cells (CTL)

The effect of recombinant human interleukin 5 (rhIL5) on the generation of CTL was investigated by using autologous EBV-transformed B cells as the target. Exogenous IL5 augmented the CTL generation, and its effect was most active at the concentration of 10 ng/ml, and when added at the late phase of culture in this system. IL5 augmented specific CTL activity rather than MHC nonrestricted CTL activity as detected with K562 and Daudi when compared to that augmented by IL2. IL5 did not increase the expression of p55 or p75 IL2R nor the responsiveness to IL2. Taken together with the finding that IL5 augmented the CTL activity even in the presence of cyclosporin A, the effect of IL5 on the CTL generation seems not to act through the IL2-IL2R system.

Production and purification of recombinant human interleukin-5 from yeast and baculovirus expression systems

A cDNA for human interleukin-5 (hIL-5) was created from the hIL-5 gene using site-directed mutagenesis to splice out the introns in vitro. This cDNA was expressed in yeast and baculovirus systems, utilizing in both cases an in-frame fusion to the pre sequence of the alpha-mating-type factor to direct secretion. The highest level of production was achieved from Sf9 cells using a baculovirus vector in serum-containing medium (2.7 mg/l), whereas in serum-free medium ten times less hIL-5 was produced. In the yeast system much lower levels of hIL-5 were produced (12.5 micrograms/l). Recombinant hIL-5 was purified to homogeneity from serum-free baculovirus cultures. The rhIL-5 consisted of a 30-kDa homodimer linked by disulfide bridging. The purified recombinant protein had a specific activity on murine BCL1 cells of 1.5 x 10(4) U/mg, of 3 x 10(5) U/mg in the murine eosinophil differentiation factor assay, and 2.4 x 10(7) U/mg in a human peripheral eosinophil maintenance assay.

Cytokine-induced proliferation and immunoglobulin production of human B lymphocytes triggered through their CD40 antigen

Human resting B lymphocytes enter a state of sustained proliferation when incubated with both mouse fibroblastic L cells stably expressing Fc gamma RII/CDw32 and anti-CD40 antibodies. We have explored the effects of 11 recombinant human cytokines (CKs) on induced cell proliferation and immunoglobulin (Ig) production. Interleukin 4 (IL-4) was the only CK able to enhance anti-CD40-induced B cell multiplication as measured by enumeration of viable cells, and interferon gamma (IFN-gamma) further stimulated this induced proliferation. IL-4 enhanced the production of IgM and IgG by B cells and induced them to produce IgE. Combinations of IL-4 and IL-2 resulted in the production of large amounts of IgM and IgA. Interestingly, IFN-gamma did not inhibit the production of IgE by cells stimulated with anti-CD40 and IL-4. None of the tested CK combinations resulted in the production of large quantities of IgG. Therefore, this new culture system represents a unique model to study isotype regulation in highly purified human B lymphocytes, in addition to allowing the generation of long-term factor-dependent human B cell lines.

Interleukin 5 and its receptor

IL-5 is a cytokine mainly produced by T lymphocytes, especially when they are sensitized with microorganisms, which induce eosinophils and Ly-1 positive B lineage cells, both of which are probably engaged in the primary protection against micro-organisms. These possibilities are discussed by analyzing IL-5 transgenic mice. We also discuss the possibility of using these mice as animal models for the diseases which may be caused by increased levels of eosinophils. Although IL-5 is not produced by bone marrow stromal cells, it is involved in the early development of eosinophils and Ly-1 positive B-lineage cells that can differentiate into macrophages. The clue to the role of IL-5 may exist in the constitution of IL-5 receptor. The IL-5 receptor consists of alpha and beta chains. The alpha chain is a 60 kDa glycosylated protein which binds IL-5, by itself, with low affinity. On the other hand, the 130 kDa beta chain does not bind IL-5 by itself, but forms high affinity IL-5 receptors together with the alpha chain. Surprisingly, this beta chain is probably shared with the GM-CSF receptor and is very homologous to the IL-3 receptor. It seems that the beta chain is expressed in the very early stage of hematopoiesis. The alpha chain may be directly related to the cell lineage commitment.

Interleukin 5 modifies histamine release and leukotriene generation by human basophils in response to diverse agonists

Human interleukin 5 (IL-5), known as a selective colony-stimulating factor of the eosinophil lineage and activator of mature eosinophils, also profoundly influences the mediator release profile of human basophils. IL-5 by itself triggers neither granule release nor de novo synthesis of lipid mediators. However, at low concentrations (0.1-10 ng/ml), IL-5 rapidly primes basophils for enhanced histamine release and leukotriene C4 (LTC4) generation in response to all established basophil agonists. LTC4 generation is more strongly affected by IL-5 than histamine release. In particular, IL-5 renders basophils capable of producing large quantities of LTC4 in response to C5a, which, without the cytokine, induces histamine release only. Finally, IL-5 renders basophils responsive to agonists (neutrophil-activating peptide 1 and C3a), which are otherwise inefficient triggers for basophil mediator release. The effects are similar to the recently established bioactivity of IL-3 on basophils, with the exception of its influence on IgE-dependent basophil activation, which is less pronounced. Thus, IL-5 strongly modulates the function not only of eosinophils but also of basophils, the two major effector leukocyte types involved in allergic inflammatory processes, e.g., in asthma.

Expression of the murine interleukin-5 receptor on Xenopus laevis oocytes

In this study we describe the use of Xenopus laevis oocytes for the detection of mRNA coding for a murine interleukin-5 (mI15) receptor. When injected with sucrose gradient fractionated polyA+ RNA derived from the murine 115-dependent pre B cell line B13, these oocytes could specifically bind 35S-methionine labeled mI15. A size of approximately 4000 nucleotides (25S) was estimated for the mRNA corresponding to the mIL5-binding activity. This binding was not blocked by a monoclonal antibody R52 specific for the MI15-receptor, suggesting that the oocytes express a different form of this receptor.

Preparation and characterization of human interleukin-5 expressed in recombinant Escherichia coli

The gene coding for human interleukin-5 was synthesized and expressed in Escherichia coli under control of a heat-inducible promoter. High-level expression, 10-15% of total cellular protein, was achieved in E. coli. The protein was produced in an insoluble state. A simple extraction, renaturation and purification scheme is described. The recombinant protein was found to be a homodimer, similar to the natural murine-derived protein. Despite the lack of glycosylation, high specific activities were obtained in three 'in vitro' biological assays. Physical characterization of the protein showed it to be mostly alpha-helical, supporting the hypothesis that a conformational similarity exists among certain cytokines.

Characterization of interleukin 5 receptors on eosinophilic sublines from human promyelocytic leukemia (HL-60) cells

The T cell product interleukin 5 (IL-5) has been shown to be a key factor in the development and the maturation of the eosinophilic cell lineage. We report here on the detection of human IL-5 receptors on eosinophilic sublines of the promyelocytic leukemia HL-60. Sodium butyrate, which initiates differentiation to mature eosinophils, also induces the appearance of high affinity (Kd 1-5 X 10(-11) M) IL-5 binding sites on these cells. The receptors are specific for IL-5, since binding of radiolabeled ligand can only be inhibited with homologous or murine IL-5 and not by other cytokines. We further show that the receptors are functional, since IL-5 can stimulate the proliferation of these cells. Affinity crosslinking of surface-bound 125I human IL-5 or 35S mouse IL-5 identified two membrane polypeptides of approximately 60 and approximately 130 kD to which IL-5 is closely associated. The presence of granulocyte/macrophage-colony-stimulating factor or tumor necrosis factor during butyrate induction decreased the expression of IL-5 binding sites compared with control cultures. The identification and characterization of human IL-5 receptors on HL-60 sublines should provide new insight into the role of this cytokine in eosinophil differentiation.

Cytokines and Ig switching: evolutionary divergence between mice and humans

Cytokines exert control over many aspects of immunoglobulin regulation, including isotype switching. But is the same mechanism used in subclass regulation in mice and humans? Robin Callard and Malcolm Turner think not, and here caution against the wholesale application of murine studies to humans.

In vitro and in vivo studies with purified recombinant human interleukin 5

The functional activities of highly purified recombinant human IL 5 (hIL 5) have been characterized on a number of cell types in vitro and in BALB/c mice in vivo. In vitro, hIL 5 could induce the differentiation of eosinophils from precursors in both human and mouse bone marrow with approximately the same efficiency. A mouse IL 5/3-dependent B cell line, LyH7.B13, was found to proliferate in response to hIL 5 but not human interleukin 1 (IL 1), interleukin 2 (IL 2), interleukin 3 (IL 3), interleukin 4 (IL 4), interleukin 6 (IL 6), interferon-gamma (IFN-gamma), or granulocyte macrophage-colony stimulating factor (GM-CSF) and was at least 10-fold more sensitive than BCL1 mouse lymphoma cells. We have successfully used this cell line to demonstrate the production of IL 5 by human T cell clones. In marked contrast to its effects on murine B cell lines, hIL 5 had no demonstrable activity on CD23 expression, anti-mu costimulated proliferation or IgM, IgG, or IgE production by tonsillar B cells and did not influence such responses triggered by IL 4. BALB/c mice injected with hIL 5 for 7 consecutive days were shown to develop an eosinophilia comparable to that induced by infection with the parasite Mesocestoid corti.

The role of human interleukin-6 in B-cell isotype regulation and differentiation

Human Interleukin-6 (IL-6) is a cytokine secreted by T cells, as well as a variety of other cell types, which exhibits B-cell differentiating activity. The recent cloning of the gene that codes for this molecule has allowed us the opportunity to study the function of this molecule alone and in conjunction with other lymphokines in human B-cell isotype-regulation and differentiation. Recombinant human IL-6 enhances immunoglobulin (Ig) M and G secretion by B-cells activated by Staphylococcal A Cowan strain (SAC) and enhances IgM, IgG, and IgA secretion by B-cells activated by pokeweed mitogen. IL-6 also augments immunoglobulin secretion of differing isotypes from various Epstein-Barr Virus transformed B-cell lines. However, IL-6 does not alter the secreted isotype of naive surface IgM-positive B-cells. As human T-cells secrete other lymphokines in association with IL-6 after activation we examined the interaction of Interleukin-2 (IL-2) gamma-interferon (IFN-gamma) and Interleukin-4 (IL-4) with IL-6 on B-cell immunoglobulin secretion. IL-2 and IL-4 synergized with IL-6 in augmenting immunoglobulin secretion by SAC-activated B-cells. IFN-gamma significantly inhibited the Ig secretion of SAC-activated B-cells cocultured with IL-6 alone or in combination with IL-2. These results demonstrate that human recombinant IL-6 augments immunoglobulin secretion of isotype-committed B-cells but it does not induce a change in the isotype secreted. In addition, this lymphokine synergizes with IL-2 and IL-4 in supporting Ig secretion. However, IFN-gamma significantly inhibits IL-6 induced Ig secretion.

The biological role of interleukin 5

Eosinophilia can be a specific cellular response, but the mechanisms of its control are not yet fully understood. Interleukin 5 (IL-5) is a lineage-specific eosinophil differentiation and activation factor. It can be detected in the serum of mice with eosinophilia, and antibody to IL-5 blocks the development of parasite-induced eosinophilia. The role of other cytokines in the production of eosinophil precursors is not clear, and may be in vitro artifacts. The biological significance of the B cell growth factor (BCGF) activity of murine IL-5 remains a puzzle. Although eosinophilia is often associated with high levels of IgE antibody, IL-5 appears not to be involved in this response, where interleukin 4 appears to be the main controlling factor. Understanding this activity has been made more difficult, since human IL-5 has no activity in analogous human BCGF assays. A better understanding of the role of these activities will probably come from studies in vivo rather than from cell culture.

Cytokines and bronchial hyperreactivity

Cytokines and interleukins are a potent group of molecules that is primarily involved in maintaining homeostasis. These molecules regulate the growth and function of many cells of the immune system including eosinophils, mast cells/basophils and others. Activation of the later cells by cytokines may play a crucial role in the development of allergic inflammation of the airways. The importance of cytokines in the pathogenesis of bronchial hyperreactivity and asthma has been reviewed in this paper.

Human T cell-replacing factor(s): a comparison of recombinant and purified human B cell growth and differentiation factors

Conditioned medium from phytohemagglutinin-activated T cells contains T cell-replacing factor(s) (TRF) able to restore specific antibody responses by human blood or tonsillar B cells which have been thoroughly depleted of T cells. Of twelve recombinant cytokines tested as possible candidates for TRF in conditioned media, namely human recombinant interleukin (hrIL) 1 alpha and beta, hrIL2, hrIL3, hrIL4, hrIL5, hrIL6, hrIFN-alpha and -gamma, hr granulocyte macrophage colony-stimulating factor (hrGM-CSF) and tumor necrosis factor (hr TNF)-alpha and -beta only IL2 was found to have TRF activity. In addition, a semi-purified low molecular weight B cell growth factor (BCGFlow) also had TRF activity. As the commercially available BCGFlow is known to contain low concentrations of IL2, IFN-gamma, TNF and GM-CSF as impurities, it was important to exclude these as being responsible for the TRF activity. At the concentrations present in BCGFlow (less than 0.2 U/ml), IL2 was not active in the TRF assay. In contrast, a combination of IL2 (0.2 U/ml), IFN-gamma (50 U/ml), TNF-alpha (50 U/ml) and TNF-beta (100 U/ml) did have TRF activity suggesting that B cells could be made to respond to low doses of IL2 by the presence of other cytokines. Although this finding raises important questions about the nature of TRF in conditioned medium, the TRF activity of BCGFlow was unlikely to be due to such a synergistic combination of cytokines for the following reasons. First, in several experiments, responses were obtained with BCGFlow, but not with IL2 or combinations of IL2 with IFN and TNF. Second, antibody to IL2 was found to inhibit the TRF activity of IL2 but not of BCGFlow. Taken together these findings show that two distinct cytokines (IL2 and BCGFlow) are TRF for human B cells. However, some combinations of cytokines can also have TRF activity underlining the complexities which can arise from working with semi-purified rather than recombinant factors.