Characterization of a receptor for interleukin 5 on human eosinophils: variable expression and induction by granulocyte/macrophage colony-stimulating factor

Reconstitution of the functional receptors for murine and human interleukin 5

The murine interleukin 5 receptor (mIL-5R) is composed of two distinct subunits, alpha and beta. The alpha subunit (mIL-5R alpha) specifically binds IL-5 with low affinity. The beta subunit (mIL-5R beta) does not bind IL-5 by itself, but forms the high-affinity receptor with mIL-5R alpha. mIL-5R beta has been revealed to be the mIL-3R-like protein, AIC2B which is shared with receptors for IL-3 and granulocyte/macrophage colony-stimulating factor. We demonstrated here the reconstitution of the functional receptors for murine and human IL-5 on the mouse IL-2-dependent cell line, CTLL-2. CTLL-2 was transfected with the cDNAs for mIL-5R alpha and/or AIC2B. Only CTLL-2 transfectant expressing both mIL-5R alpha and AIC2B expressed the high-affinity receptor and proliferated in response to murine IL-5. Then CTLL-2 was transfected with the cDNAs for hIL-5R alpha and/or KH97 (beta c), the human homologue of AIC2B. Though beta c did not contribute much to binding affinity of hIL-5R, only CTLL-2 transfectant expressing both hIL-5R alpha and beta c proliferated in response to human IL-5. These results showed that the beta subunit is indispensable in IL-5 signal transduction. We further investigated the function of IL-5-specific alpha subunit in transmitting IL-5 signals. Mutant mIL-5R alpha, which lacks its whole cytoplasmic domain, was transfected into mouse IL-3-dependent cell line, FDC-P1 expressing AIC2B intrinsically. The resulting transfectant did not respond to IL-5, though the transfectant expressed the high-affinity IL-5R, indicating that the cytoplasmic portion of the alpha subunit also has some important role in IL-5-mediated signal transduction.

The involvement of eosinophils in the patch test reaction to aeroallergens in atopic dermatitis: its relevance for the pathogenesis of atopic dermatitis

Atopic dermatitis (AD) is considered a T-cell mediated disease. Activated T-cells, mainly of the CD4-subtype, are abundantly present in lesional AD skin. Although not many intact eosinophils are present, deposits of eosinophil derived major-basic-protein (MBP) and eosinophil-cationic-protein (ECP) suggest eosinophil involvement. After patch testing AD patients with aeroallergens, an eczematous reaction develops after 24-48 hr at the site of application. This patch test reaction shows macroscopic resemblance to lesional AD skin and does not take place in normal individuals, asthma and allergic rhinitis patients. Lymphocytes together with eosinophils infiltrate into the dermis 2-6 hr after allergen application. Twenty-four to forty-eight hours after patch testing, eosinophils are in an activated state since they release ECP (being EG2-positive). At this point in time eosinophils have also infiltrated the epidermis. Here they are EG2-negative. Forty-eight to seventy-two hours after patch testing the eczematous reaction decreases. This coincides with disappearance of eosinophils from both the dermis and the epidermis; then, a dendritic staining pattern can be observed in the epidermis with anti-eosinophil peroxidase. Thus, eosinophils infiltrate the dermis and epidermis after patch testing AD patients with aeroallergens and release part of their granular constituents. Recent in vitro investigations revealed that eosinophils from the circulation of AD patients react more powerfully in in vitro test systems such as chemiluminescence, chemotaxis and endothelial adherence and transmigration. It is very likely that this activated (= primed) state is caused by the influence of lymphocyte-derived cytokines like IL-3, IL-5 and GM-CSF, since activated lymphocytes in the circulation (and tissue) may release these cytokines. The primed state of the eosinophils may facilitate tissue infiltration. The subsequent activation of eosinophils within the tissue leading to mediator release and the function of these mediators need to be further elucidated. The close similarity between the cellular events after a patch test reaction to aeroallergens in AD patients and those present in lesional AD skin suggests that the patch test reaction may be a helpful in vivo model to study the pathogenesis of AD. The prominent involvement of lymphocytes and eosinophils in this reaction also suggests some similarity with late phase reactions (LPR) observed in the skin after intracutaneous allergen challenge.

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.

Interleukin-7 expression during mouse thymus development

We have monitored the expression of interleukin-7 (IL-7) in the developing embryonic mouse thymus by a combination of quantitative polymerase chain reaction (PCR) and immunofluorescence microscopy. A strong specific signal for IL-7 mRNA was detected by day 12 in the developing fetal thymus. IL-7 mRNA was found to be maximally expressed on day 15, and then decreased over the next 5 days. Immunofluorescence staining of fetal thymus sections using an anti-IL-7 antibody confirmed these PCR data. IL-7 protein expression was first detected at day 13 of development. At 14 days the intensity of the staining increased by a factor of three and stayed at this level over the next 4 days. The same anti-IL-7 antibody used for immunofluorescence, blocked the proliferation of fetal thymocytes in organotypic cultures. In addition, we detected mRNA coding for IL-2 and SCF (also known as the steel factor or KL) in embryonic thymocytes. The implications of these findings for early thymocyte growth are discussed.

Mature eosinophils stimulated to develop in human-cord blood mononuclear cell cultures supplemented with recombinant human interleukin-5. II. Vesicular transport of specific granule matrix peroxidase, a mechanism for effecting piecemeal degranulation

The mechanism of piecemeal degranulation by human eosinophils was investigated. Mature eosinophils that developed in rhIL-5-containing conditioned media from cultured human cord blood mononuclear cells were prepared for ultrastructural studies using a combined technique to image eosinophil peroxidase by cytochemistry in the same sections on which postembedding immunogold was used to demonstrate Charcot-Leyden crystal protein. Vesicular transport of eosinophil peroxidase from the specific granule matrix compartment to the cell surface was associated with piecemeal degranulation. This process involved budding of eosinophil peroxidase-loaded vesicles and tubules from specific granules. Some eosinophil peroxidase that was released from eosinophils remained bound to the cell surface; some was free among the cultured cells. Macrophages and basophils bound the released eosinophil peroxidase to their plasma membranes, internalized it in endocytotic vesicles, and stored it in their respective phagolysosomes and secretory granules. Charcot-Leyden crystal protein was diffusely present in the nucleus and cytoplasm of IL-5-stimulated mature eosinophils. Extensive amounts were generally present in granule-poor and subplasma membrane areas of the cytoplasm in contrast to eosinophil peroxidase, which was secreted and bound to the external surface of eosinophil plasma membranes. These studies establish vesicular transport as a mechanism for emptying the specific eosinophil granule matrix compartment during IL-5-associated piecemeal degranulation.

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.

The role of GM-CSF in infection

GM-CSF is a hemopoietic growth factor with substantial effects on the proliferation of neutrophils, eosinophils and monocytes/macrophages. Its physiologic role in infection is still poorly understood. The gene for GM-CSF is constitutively transcribed in cells substantial for antiinfectious response. Various cells are activated and induced by TNF and IL-1 to synthesize GM-CSF. No systemic GM-CSF levels can be detected in patients with infection. It is likely that GM-CSF plays its physiological role in the immediate vicinity of the cells by which it is secreted. GM-CSF functionally activates neutrophils, monocytes/macrophages and eosinophils. It may augment T-cell proliferation and function. GM-CSF is effective in mice infected with Staphylococcus aureus or Salmonella typhimurium. Its effect in infectious disease in man should be explored.

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.

Eosinophils: a review

The eosinophil was discovered by Jones in 1846 (Dessein and David, 1982) but its proclivity to stain with aniline dyes was first described by Paul Ehrlich in 1879 (Hirsch and Hirsch, 1980). Recognized and named for this quality, eosinophils possess an abundance of highly basic proteins within their granules which confer their affinity for acidic dyes (Gleich and Loegering, 1984). Eosinophils are traditionally viewed as killer-effector cells in parasitic infestations and as modulators of Type I hypersensitivity reactions (Butterworth and David, 1981; Kay, 1985). The eosinophils' reserve of cationic proteins and enzymes which imparts their profound parasiticidal effects (Butterworth and David, 1981) contrasts with this leukocyte's purported regulatory function in inflammation (Kay, 1985; Fechter et al., 1986). The opposing functions possessed by this leukocyte exemplify the enigma of the eosinophil. Recent evidence suggests that although the eosinophil does posses some regulatory capabilities, its presence is, in fact, a harbinger of tissue destruction (Gleich and Adolphoson, 1986, Wardlaw and Kay, 1987; Spry, 1988). Nor does the presence of the eosinophil automatically infer IgE mediated hypersensitivity, as evidenced by studies examining the interaction of the eosinophil with the cellular arm of the immune system (Basten and Beeson, 1970; Ruscetti et al., 1976; Beeson and Bass, 1977; Raghavachar et al., 1987; Ohnishi et al., 1988). The purpose of this review is to provide a brief overview of the structure and biology of the mammalian eosinophil and to emphasize the fact that eosinophils fulfil a paradoxical role as effectors of tissue damage and as benign modulators of inflammation.

Cytokine regulation of eosinophil function

The development and function of eosinophils are regulated by a number of cytokines. Three cytokines have major effects on eosinophilopoiesis. Both granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 stimulate the development of eosinophils as well as other leukocytes. Interleukin-5 promotes eosinophil development and terminal differentiation. These three cytokines also effect the functions of mature eosinophils and can prolong their longevity in in vitro culture, enhance their capacity for release of leukotriene C4 (LTC4), augment their capacity for helminthotoxicity and degranulation, and render them less dense ("hypodense") than normal, unactivated eosinophils. GM-CSF can also induce the expression of HLA-DR on mature eosinophils, which can enable eosinophils to serve as antigen-presenting cells in stimulating T-cell responses. A T-cell-derived cytokine, lymphocyte chemoattractant factor (LCF), which stimulates the migration and function of CD4+ lymphocytes and eosinophils, also utilizes CD4 expressed on human eosinophils as its receptor. LCF stimulates eosinophil migration but not degranulation, leukotriene C4 release, or respiratory burst activity. Interleukin-2 is also a potent chemoattractant for eosinophils. Thus, cytokines are involved in both increased production of eosinophils as well as regulation of the functions of mature eosinophils. These functions of mature eosinophils include effector functions and collaborative interactions with lymphocytes and other tissue cellular elements.

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.

Interleukin-5-induced granulocyte activation in atopic patients

The effect of recombinant human and murine interleukin-5 (IL-5) on granulocytes was investigated in patients with atopic dermatitis (AD) and allergic rhinitis and compared with those from patients with plaque psoriasis and normal non-atopic controls. Granulocyte activation was measured as lucigenin-dependent chemiluminescence (CL) and release of eosinophil cationic protein (ECP) as well as by scanning- and transmission-electron microscopy (EM) and the ultrastructural detection of production of H2O2. A significant direct effect of both human and murine IL-5 on granulocyte oxidative metabolism could only be detected in those patients with AD and allergic rhinitis. Also, as compared to normal controls, significantly increased CL responses were observed in these patients with stimulation with other granulocyte-activating cytokines, particularly GM-CSF. In patients with psoriasis there was no significant increase in response to stimulation with TNF alpha, TNF beta or GM-CSF, but IL-5 induced slight but significant CL responses in the granulocytes. None of the cytokines tested significantly stimulated the release of ECP in any of the groups. Ultrastructural studies showed that stimulation with human as well as murine IL-5 produced significant morphological changes in both eosinophils and polymorphonuclear neutrophilic granulocytes from the patients with AD. Production of H2O2 was visualized at the luminal part of the intracytoplasmic vesicles of the granulocytes and at the points of contact between the cells. On morphometric analysis, almost all the polymorphonuclear neutrophils in the patients with AD appeared to be activated, whereas only some of these cells in the normal controls showed signs of activation.

Effects of IL-5, granulocyte/macrophage colony-stimulating factor (GM-CSF) and IL-3 on the survival of human blood eosinophils in vitro

The mechanisms that could affect the lifespan of eosinophils after they have left the bone marrow, and their capacity to respond to activation factors were studied by examining the effects of IL-5, GM-CSF and IL-3 on purified human blood eosinophils in culture. All three cytokines prolonged the lifespan of the majority of blood eosinophils. This effect was dose-dependent: IL-5 greater than GM-CSF greater than IL-3. Light density eosinophils from most patients had a longer lifespan in culture than did normal density eosinophils, with or without the three cytokines. Eosinophil death in the absence of these cytokines occurred by apoptosis. Eosinophils from two patients did not survive when cultured with IL-5, although they survived in the presence of IL-3 or GM-CSF. IL-5, GM-CSF and IL-3 induced the expression of the activation epitope on the eosinophil ribonucleases recognized by monoclonal antibody EG2. We conclude that small amounts of IL-5, GM-CSF and IL-3 prevented programmed cell death in human blood eosinophils and induced the expression of the activation forms of eosinophil ribonucleases. We suggest that differences in the capacity of normal and light density eosinophils to survive in culture, and in the ability of eosinophils from some patients to respond to IL-5 could account for variations in the severity of disease seen in patients with persistent eosinophilia.

Analysis of interleukin 5 receptors on murine eosinophils: a comparison with receptors on B13 cells

The interleukin 5 receptor (IL-5R) on murine eosinophils and a mouse B cell line (B13) was investigated using iodinated murine IL-5 produced in the baculovirus system. Electrophoretic analysis of this recombinant protein identified a range of bands Mr 26,000 to 32,000 resulting from differential glycosylation. The specific activity and binding kinetics of the iodinated IL-5 (125I-IL-5) were essentially identical to unlabeled material. Both high-affinity (Kd approximately 50 pM) and low-affinity (Kd approximately 1 nM) receptor populations were identified on murine eosinophils. Approximately 50 high-affinity receptors and 10,000 low-affinity receptors were present. This was compared with approximately 2,000 high-affinity (Kd approximately 80 pM) and about 8,000 low-affinity (Kd approximately 3 nM) sites on B13 cells. An antibody that inhibits IL-5 binding to, and proliferation of, B13 cells (R52.120) was also shown to inhibit eosinophil proliferation, suggesting that eosinophils and B cells bear the equivalent IL-5 binding proteins.

Human eosinophils from hypereosinophilic patients spontaneously express the p55 but not the p75 interleukin 2 receptor subunit

The expression of interleukin 2 receptor (IL2R) on eosinophils was investigated in patients with hypereosinophilia. Hypodense activated eosinophils have been described in various diseases such as parasitic or allergic diseases, hypereosinophilic syndrome (HES) associated in some cases to myeloproliferative markers, and more recently described in patients undergoing recombinant IL2 treatment. The presence of p55 alpha chain of IL2R (CD25) on purified eosinophils collected from blood of hypereosinophilic patients was detected by flow cytometry. In 10 out of 19 cases, more than 10% of eosinophils were CD25+. Cross-linking studies on enriched eosinophils showed one 64-75-kDa band, consisting of IL2 (15 kDa) cross-linked to the IL2R p55 subunit. In Northern blot analysis the two messenger mRNA (3.5 and 1.5 kb) encoding the IL2R p55 subunit were identified after hybridization with a CD25 cDNA probe. In contrast, the presence of the IL2R p75 subunit was not detected. These data provide preliminary evidence for the expression of a low-affinity receptor for IL2 on in vivo activated eosinophils and raise the question of the role played by this cytokine in eosinophil differentiation and activation.

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.