Reciprocal inhibition of binding between interleukin 3 and granulocyte-macrophage colony-stimulating factor to human eosinophils

Efficient production of human interleukin-3 from Escherichia coli using protein disulfide isomerase b'a' domain

Human interleukin-3 (IL3) is a multifunctional cytokine essential for both clinical and biomedical research endeavors. However, its production in Escherichia coli has historically been challenging due to its aggregation into inclusion bodies, requiring intricate solubilization and refolding procedures. This study introduces an innovative approach employing two chaperone proteins, maltose binding protein (MBP) and protein disulfide isomerase b'a' domain (PDIb'a'), as N-terminal fusion tags. Histidine tag (H) was added at the beginning of each chaperone protein gene for easy purification. This fusion of chaperone proteins significantly improved IL3 solubility across various E. coli strains and temperature conditions, eliminating the need for laborious refolding procedures. Following expression optimization, H-PDIb'a'-IL3 was purified using two chromatographic methods, and the subsequent removal of the H-PDIb'a' tag yielded high-purity IL3. The identity of the purified protein was confirmed through liquid chromatography coupled with tandem mass spectrometry analysis. Biological activity assays using human erythroleukemia TF-1 cells revealed a unique two-step stimulation pattern for both purified IL3 and the H-PDIb'a'-IL3 fusion protein, underscoring the protein's functional integrity and revealing novel insights into its cellular interactions. This study advances the understanding of IL3 expression and activity while introducing novel considerations for protein fusion strategies.

Expression and regulation of Siglec-6 (CD327) on human mast cells and basophils

BACKGROUND

Mast cells (MC) and basophils are effector cells of allergic reactions and display a number of activation-linked cell surface antigens. Of these antigens, however, only a few are functionally relevant and specifically expressed in these cells.

OBJECTIVE

We sought to identify MC- and basophil-specific surface molecules and to study their cellular distribution and regulation during cytokine-induced and IgE-dependent activation.

METHODS

Multicolor flow cytometry was performed to recognize surface antigens and to determine changes in antigen expression upon activation.

RESULTS

We identified Siglec-6 (CD327) as a differentially regulated surface antigen on human MC and basophils. In the bone marrow, Siglec-6 was expressed abundantly on MC in patients with mastocytosis and in reactive states, but it was not detected on other myeloid cells, with the exception of basophils and monocytes. In healthy individuals, allergic patients, and patients with chronic myeloid leukemia (CML), Siglec-6 was identified on CD203c⁺ blood basophils, a subset of CD19⁺ B lymphocytes, and few CD14⁺ monocytes, but not on other blood leukocytes. CML basophils expressed higher levels of Siglec-6 than normal basophils. IL-3 promoted Siglec-6 expression on normal and CML basophils, and stem cell factor increased the expression of Siglec-6 on tissue MC. Unexpectedly, IgE-dependent activation resulted in downregulation of Siglec-6 in IL-3-primed basophils, whereas in MC, IgE-dependent activation augmented stem cell factor-induced upregulation of Siglec-6.

CONCLUSIONS

Siglec-6 is a dynamically regulated marker of MC and basophils. Activated MC and basophils exhibit unique Siglec-6 responses, including cytokine-dependent upregulation and unique, cell-specific, responses to IgE-receptor cross-linking.

Dual Role of GM-CSF as a Pro-Inflammatory and a Regulatory Cytokine: Implications for Immune Therapy

Granulocyte macrophage colony stimulating factor (GM-CSF) is generally recognized as an inflammatory cytokine. Its inflammatory activity is primarily due its role as a growth and differentiation factor for granulocyte and macrophage populations. In this capacity, among other clinical applications, it has been used to bolster anti-tumor immune responses. GM-CSF-mediated inflammation has also been implicated in certain types of autoimmune diseases, including rheumatoid arthritis and multiple sclerosis. Thus, agents that can block GM-CSF or its receptor have been used as anti-inflammatory therapies. However, a review of literature reveals that in many situations GM-CSF can act as an anti-inflammatory/regulatory cytokine. We and others have shown that GM-CSF can modulate dendritic cell differentiation to render them "tolerogenic," which, in turn, can increase regulatory T-cell numbers and function. Therefore, the pro-inflammatory and regulatory effects of GM-CSF appear to depend on the dose and the presence of other relevant cytokines in the context of an immune response. A thorough understanding of the various immunomodulatory effects of GM-CSF will facilitate more appropriate use and thus further enhance its clinical utility.

Human airway eosinophils exhibit preferential reduction in STAT signaling capacity and increased CISH expression

Allergic asthma, a chronic respiratory disorder marked by inflammation and recurrent airflow obstruction, is associated with elevated levels of IL-5 family cytokines and elevated numbers of eosinophils (EOS). IL-5 family cytokines elongate peripheral blood EOS (EOS(PB)) viability, recruit EOS(PB) to the airways, and, at higher concentrations, induce degranulation and reactive oxygen species generation. Although airway EOS (EOS(A)) remain signal ready in that GM-CSF treatment induces degranulation, treatment of EOS(A) with IL-5 family cytokines no longer confers a survival advantage. Because the IL-5 family receptors have common signaling capacity, but are uncoupled from EOS(A) survival, whereas other IL-5 family induced endpoints remain functional, we tested the hypothesis that EOS(A) possess a JAK/STAT-specific regulatory mechanism (because JAK/STAT signaling is critical to EOS survival). We found that IL-5 family-induced STAT3 and STAT5 phosphorylation is attenuated in EOS(A) relative to blood EOS from airway allergen-challenged donors. However, IL-5 family-induced ERK1/2 phosphorylation is not altered between EOS(A) and EOS from airway allergen-challenged donors. These observations suggest EOS(A) possess a regulatory mechanism for suppressing STAT signaling distinct from ERK1/2 activation. Furthermore, we found, in EOS(PB), IL-5 family cytokines induce members of the suppressors of cytokine signaling (SOCS) genes, CISH and SOCS1. Additionally, following allergen challenge, EOS(A) express significantly more CISH and SOCS1 mRNA and CISH protein than EOS(PB) counterparts. In EOS(PB), long-term pretreatment with IL-5 family cytokines, to varying degrees, attenuates IL-5 family-induced STAT5 phosphorylation. These data support a model in which IL-5 family cytokines trigger a selective downregulation mechanism in EOS(A) for JAK/STAT pathways.

The GM-CSF/IL-3/IL-5 cytokine receptor family: from ligand recognition to initiation of signaling

Granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5 are members of a discrete family of cytokines that regulates the growth, differentiation, migration and effector function activities of many hematopoietic cells and immunocytes. These cytokines are involved in normal responses to infectious agents, bridging innate and adaptive immunity. However, in certain cases, the overexpression of these cytokines or their receptors can lead to excessive or aberrant initiation of signaling resulting in pathological conditions, with chronic inflammatory diseases and myeloid leukemias the most notable examples. Recent crystal structures of the GM-CSF receptor ternary complex and the IL-5 binary complex have revealed new paradigms of cytokine receptor activation. Together with a wealth of associated structure-function studies, they have significantly enhanced our understanding of how these receptors recognize cytokines and initiate signals across cell membranes. Importantly, these structures provide opportunities for structure-based approaches for the discovery of novel and disease-specific therapeutics. In addition, recent biochemical evidence has suggested that the GM-CSF/IL-3/IL-5 receptor family is capable of interacting productively with other membrane proteins at the cell surface. Such interactions may afford additional or unique biological activities and might be harnessed for selective modulation of the function of these receptors in disease.

Eosinophils induce airway smooth muscle cell proliferation

Asthma is characterized by eosinophilic airway inflammation and remodeling of the airway wall. Features of airway remodeling include increased airway smooth muscle (ASM) mass. However, little is known about the interaction between inflammatory eosinophils and ASM cells. In this study, we investigated the effect of eosinophils on ASM cell proliferation. Eosinophils were isolated from peripheral blood of mild asthmatics and non-asthmatic subjects and co-cultured with human primary ASM cells. ASM proliferation was estimated using Ki-67 expression assay. The expression of extracellular matrix (ECM) mRNA in ASM cells was measured using quantitative real-time PCR. The role of eosinophil derived Cysteinyl Leukotrienes (CysLTs) in enhancing ASM proliferation was estimated by measuring the release of leukotrienes from eosinophils upon their direct contact with ASM cells using ELISA. This role was confirmed either by blocking eosinophil-ASM contact or co-culturing them in the presence of leukotrienes antagonist. ASM cells co-cultured with eosinophils, isolated from asthmatics, but not non-asthmatics, had a significantly higher rate of proliferation compared to controls. This increase in ASM proliferation was independent of their release of ECM proteins but dependent upon eosinophils release of CysLTs. Eosinophil-ASM cell to cell contact was required for CysLTs release. Preventing eosinophil contact with ASM cells using anti-adhesion molecules antibodies, or blocking the activity of eosinophil derived CysLTs using montelukast inhibited ASM proliferation. Our results indicated that eosinophils contribute to airway remodeling during asthma by enhancing ASM cell proliferation and hence increasing ASM mass. Direct contact of eosinophils with ASM cells triggers their release of CysLTs which enhance ASM proliferation. Eosinophils, and their binding to ASM cells, constitute a potential therapeutic target to interfere with the series of biological events leading to airway remodeling and Asthma.

The role of granulocyte colony-stimulating factor in the neutrophilia observed in the fetal inflammatory response syndrome

OBJECTIVES

Fetal neutrophilia is present in two-thirds of cases with the fetal inflammatory response syndrome (FIRS). The mechanisms responsible for this finding have not been elucidated. Granulocyte colony-stimulating factor (G-CSF) is the primary physiologic regulator of neutrophil production and plays a key role in the rapid generation and release of neutrophils in stressful conditions (i.e., infection). The objective of this study was to determine: 1) whether FIRS was associated with changes in fetal plasma G-CSF concentrations; and 2) if fetal plasma G-CSF concentrations correlated with fetal neutrophil counts, chorioamnionitis, neonatal morbidity/mortality and cordocentesis-to-delivery interval.

STUDY DESIGN

Percutaneous umbilical cord blood sampling was performed in a population of patients with preterm labor (n=107). A fetal plasma interleukin-6 (IL-6) concentration >11 pg/mL was used to define FIRS. Cord blood G-CSF was measured by a sensitive and specific immunoassay. An absolute neutrophil count was determined and corrected for gestational age. Receiver operating characteristic (ROC) curve, survival analysis and Cox proportional hazard model were employed.

RESULTS

1) G-CSF was detected in all fetal blood samples; 2) fetuses with FIRS had a higher median fetal plasma G-CSF concentration than those without FIRS (P<0.001); 3) a fetal plasma G-CSF concentration ≥134 pg/mL (derived from an ROC curve) was associated with a shorter cordocentesis-to-delivery interval, a higher frequency of chorioamnionitis (clinical and histological), intra-amniotic infection, and composite neonatal morbidity/mortality than a fetal plasma concentration below this cut-off; and 4) a fetal plasma G-CSF concentration ≥134 pg/mL was associated with a shorter cordocentesis-to-delivery interval (hazard ratio 3.2; 95% confidence interval 1.8-5.8) after adjusting for confounders.

CONCLUSIONS

1) G-CSF concentrations are higher in the peripheral blood of fetuses with FIRS than in fetuses without FIRS; and 2) a subset of fetuses with FIRS with elevated fetal plasma G-CSF concentrations are associated with neutrophilia, a shorter procedure-to-delivery interval, chorio-amnionitis and increased perinatal morbidity and mortality.

The molecular biology of interleukin 6 and its receptor

Functional pleiotropy and redundancy are characteristic features of cytokines. Interleukin 6 (IL-6) is a typical example: IL-6 induces cellular differentiation or expression of tissue-specific genes; it is involved in processes such as antibody production in B cells, acute-phase protein synthesis in hepatocytes, megakaryocyte maturation, cytotoxic T cell differentiation, and neural differentiation of PC12 (pheochromocytoma) cells. It promotes growth of myeloma/plasmacytoma cells, T cells, keratinocytes and renal mesangial cells, and it inhibits growth of myeloid leukaemic cell lines and certain carcinoma cell lines. The IL-6 receptor consists of two polypeptide chains, a ligand-binding chain (IL-6R) and a non-ligand-binding, signal-transducing chain (gp130). Interaction of IL-6 with IL-6R triggers the association of gp130 and IL-6R, and the signal can be transduced through gp130. Association of gp130 with IL-6R is involved in the formation of high affinity binding sites. This two-chain model has been shown to be applicable to receptor systems for several other cytokines, such as granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-3, IL-5 and nerve growth factor (NGF). The pleiotropy and redundancy of cytokines may be explained on the basis of this unique receptor system.

Empirical models of the proliferative response of cytokine-dependent hematopoietic cell lines

There is an expanding need for predictive mathematical models to accelerate the optimization of cell therapy culture processes. Here we demonstrate the ability of simple mathematical models to describe quantitatively the cytokine growth-rate dependence of two human hematopoietic cell lines, TF-1 and MO7e. These cells are immortal but depend on either interleukin-3 (IL-3) or granulocyte-macrophage colony stimulating factor (GM-CSF) for their continued survival and maximal proliferation. They are also responsive to interleukin-6 (IL-6) and exhibit saturation kinetics when these cytokines are limiting. A Monod-type relationship consistently failed to fit measured cytokine dose-proliferation response curves while a Hill-type relationship showed a good fit. Cytokine interactions were first modeled by modifying the Hill-function to include an interaction parameter, gamma. This model did not indicate either synergistic or even additive effects between IL-3 and GM-CSF. Based on the reported competition between IL-3 and GM-CSF for their common receptor (beta(c)) subunit, a competitive model was also developed. This model had no new parameters beyond those obtained from single cytokine cultures and provided improved prediction of the growth rates for both cell lines exposed to combinations of IL-3 and GM-CSF over a wide range of concentrations. As expected, the competitive model failed to fit the data for IL-6 in combination with either IL-3 or GM-CSF, since IL-6 signaling does not involve the beta(c) chain of the IL-3/GM-CSF receptors. Interestingly, the cell-specific rates of GM-CSF uptake and cell proliferation were found to be uncoupled processes. Taken together, these results illustrate the utility of appropriately designed empirical models to describe the proliferative responses of hematopoietic cells to cytokine stimulation.

The effect of nasal polyp epithelial cells on eosinophil activation

OBJECTIVES/HYPOTHESIS

Eosinophil infiltration into an inflammatory site is a characteristic histological finding in patients with chronic rhinosinusitis and nasal polyps. Most of the eosinophils in chronic rhinosinusitis are activated in the nasal cavity, but the exact activation mechanism of eosinophils is unknown. The study was designed to investigate the effect of human nasal epithelial cells on the activation of eosinophils.

STUDY DESIGN

Peripheral blood eosinophils were isolated from healthy volunteers and incubated in human nasal polyp epithelial cell conditioned media (HPECM). Superoxide production and eosinophil-derived neurotoxin were measured to determine eosinophils activation. HPECMs were assayed by ELISAs for interleukin-8 (IL-8), granulocyte-macrophage colony stimulating factor (GM-CSF), eotaxin, and regulated on activation normal T expressed and secreted (RANTES). To identify the chemical mediators involved in the activation of eosinophils.

RESULTS

HPECM (n = 7) contained 31.48 ng/mL interleukin-8, 533.43 pg/mL GM-CSF, 5.90 pg/mL eotaxin, and 11.06 pg/mL RANTES. Eosinophils were activated by HPECM and inhibited only by anti-GM-CSF antibody, not by the other chemical mediators.

CONCLUSION

The results suggest that eosinophils in nasal secretions are activated by GM-CSF, which is produced by nasal epithelial cells.

The functional basis of granulocyte-macrophage colony stimulating factor, interleukin-3 and interleukin-5 receptor activation, basic and clinical implications

The cytokines granulocyte-macrophage colony stimulating factor, interleukin-3 and interleukin-5 have overlapping activities on cells expressing their receptors. This is explained by their sharing a receptor signal transduction subunit, beta c. This communal signaling subunit is also required for high affinity binding of all three cytokines. Therapeutic approaches attempting to interfere or modulate haemopoietic cells using cytokines or their analogues can in some instances be limited due to functional redundancy amongst cytokines using shared receptor signaling subunits. Therefore, a better approach would be to develop therapeutics against the shared subunit. Studies examining the GM-CSF, IL-3 and IL-5 receptors have identified the key events leading to functional receptor activation. With this knowledge, it is now possible to identify new targets for the development of a new class of antagonist that blocks the biological activity of all the cytokines utilizing beta c. This approach may be extended to other receptor systems such as IL-4 and IL-13 where receptor activation is dependent on a common signaling and binding subunit.

Simultaneous Antagonism of Interleukin-5, Granulocyte-Macrophage Colony-Stimulating Factor, and Interleukin-3 Stimulation of Human Eosinophils by Targetting the Common Cytokine Binding Site of Their Receptors

Human interleukin-5 (IL-5), granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-3 are eosinophilopoietic cytokines implicated in allergy in general and in the inflammation of the airways specifically as seen in asthma. All 3 cytokines function through cell surface receptors that comprise a ligand-specific  chain and a shared subunit (βc). Although binding of IL-5, GM-CSF, and IL-3 to their respective receptor  chains is the first step in receptor activation, it is the recruitment of βc that allows high-affinity binding and signal transduction to proceed. Thus, βc is a valid yet untested target for antiasthma drugs with the added advantage of potentially allowing antagonism of all 3 eosinophil-acting cytokines with a single compound. We show here the first development of such an agent in the form of a monoclonal antibody (MoAb), BION-1, raised against the isolated membrane proximal domain of βc. BION-1 blocked eosinophil production, survival, and activation stimulated by IL-5 as well as by GM-CSF and IL-3. Studies of the mechanism of this antagonism showed that BION-1 prevented the high-affinity binding of125I–IL-5, 125I–GM-CSF, and125I–IL-3 to purified human eosinophils and that it bound to the major cytokine binding site of βc. Interestingly, epitope analysis using several βc mutants showed that BION-1 interacted with residues different from those used by IL-5, GM-CSF, and IL-3. Furthermore, coimmunoprecipitation experiments showed that BION-1 prevented ligand-induced receptor dimerization and phosphorylation of βc, suggesting that ligand contact with βc is a prerequisite for recruitment of βc, receptor dimerization, and consequent activation. These results demonstrate the feasibility of simultaneously inhibiting IL-5, GM-CSF, and IL-3 function with a single agent and that BION-1 represents a new tool and lead compound with which to identify and generate further agents for the treatment of eosinophil-dependent diseases such as asthma.

Simultaneous Antagonism of Interleukin-5, Granulocyte-Macrophage Colony-Stimulating Factor, and Interleukin-3 Stimulation of Human Eosinophils by Targetting the Common Cytokine Binding Site of Their Receptors

Human interleukin-5 (IL-5), granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-3 are eosinophilopoietic cytokines implicated in allergy in general and in the inflammation of the airways specifically as seen in asthma. All 3 cytokines function through cell surface receptors that comprise a ligand-specific  chain and a shared subunit (βc). Although binding of IL-5, GM-CSF, and IL-3 to their respective receptor  chains is the first step in receptor activation, it is the recruitment of βc that allows high-affinity binding and signal transduction to proceed. Thus, βc is a valid yet untested target for antiasthma drugs with the added advantage of potentially allowing antagonism of all 3 eosinophil-acting cytokines with a single compound. We show here the first development of such an agent in the form of a monoclonal antibody (MoAb), BION-1, raised against the isolated membrane proximal domain of βc. BION-1 blocked eosinophil production, survival, and activation stimulated by IL-5 as well as by GM-CSF and IL-3. Studies of the mechanism of this antagonism showed that BION-1 prevented the high-affinity binding of125I–IL-5, 125I–GM-CSF, and125I–IL-3 to purified human eosinophils and that it bound to the major cytokine binding site of βc. Interestingly, epitope analysis using several βc mutants showed that BION-1 interacted with residues different from those used by IL-5, GM-CSF, and IL-3. Furthermore, coimmunoprecipitation experiments showed that BION-1 prevented ligand-induced receptor dimerization and phosphorylation of βc, suggesting that ligand contact with βc is a prerequisite for recruitment of βc, receptor dimerization, and consequent activation. These results demonstrate the feasibility of simultaneously inhibiting IL-5, GM-CSF, and IL-3 function with a single agent and that BION-1 represents a new tool and lead compound with which to identify and generate further agents for the treatment of eosinophil-dependent diseases such as asthma.

Familial eosinophilia maps to the cytokine gene cluster on human chromosomal region 5q31-q33

Familial eosinophilia (FE) is an autosomal dominant disorder characterized by peripheral hypereosinophilia of unidentifiable cause with or without other organ involvement. To localize the gene for FE, we performed a genomewide search in a large U.S. kindred, using 312 different polymorphic markers. Seventeen affected subjects, 28 unaffected bloodline relatives, and 8 spouses were genotyped. The initial linkage results from the genome scan provided evidence for linkage on chromosome 5q31-q33. Additional genotyping of genetic markers located in this specific region demonstrated significant evidence that the FE locus is situated between the chromosome 5q markers D5S642 and D5S816 (multipoint LOD score of 6.49). Notably, this region contains the cytokine gene cluster, which includes three genes-namely, those for interleukin (IL)-3, IL-5, and granulocyte/macrophage colony-stimulating factor (GM-CSF)-whose products play important roles in the development and proliferation of eosinophils. These three cytokine genes were screened for potential disease-specific mutations by resequencing of a subgroup of individuals from the present kindred. No functional sequence polymorphisms were found within the promoter, the exons, or the introns of any of these genes or within the IL-3/GM-CSF enhancer, suggesting that the primary defect in FE is not caused by a mutation in any one of these genes but, rather, is caused by another gene in the area.

Cytokine-induced protein tyrosine phosphorylation is essential for cytokine priming of human eosinophils

BACKGROUND

Human eosinophils are strongly modulated by the eosinophilotrophic cytokines IL-5, IL-3, and granulocyte-macrophage colony-stimulating factor (GM-CSF). A clear intracellular effect of these cytokines is the induction of tyrosine phosphorylation of multiple cellular substrates. However, the relevance of tyrosine phosphorylation for eosinophil functioning has not been established.

OBJECTIVE

In this study we have investigated dose-response and time curves of IL-5-, IL-3-, and GM-CSF-induced tyrosine phosphorylation in eosinophils. Moreover, we have evaluated the importance of IL-5-induced tyrosine phosphorylation for priming of human eosinophils.

METHODS

Cytokine-induced tyrosine phosphorylation was monitored on western blot with an antiphosphotyrosine antibody (4G10). To probe the relevance of tyrosine phosphorylation for priming, eosinophils were primed with IL-5 in the presence of the tyrosine kinase inhibitor herbimycin A. Platelet activating factor (PAF) was used as a control priming agent. Subsequently, the eosinophils were incubated with serum-treated zymosan (STZ) to activate the respiratory burst. Binding of STZ was determined by FACS analysis.

RESULTS

IL-5-, IL-3-, and GM-CSF-induced tyrosine phosphorylation was found at concentrations that primed eosinophil effector mechanism (median effective dose values: approximately 5.10(-11) mol/L, approximately 5.10(-10) mol/L, and approximately 5.10(-12) mol/L for IL-5, IL-3, and GM-CSF, respectively). Cytokine-induced tyrosine phosphorylation was transient with an optimum value at 15 minutes. IL-5 priming of STZ-induced activation of the respiratory burst was blocked by herbimycin A, whereas PAF still primed this response. In fact, herbimycin A inhibited IL-5 priming of STZ binding to human eosinophils. On the other hand, PAF priming of STZ binding was not affected by herbimycin A. Both IL-5-induced and PAF-induced tyrosine phosphorylation were inhibited by herbimycin A.

CONCLUSION

These data demonstrate for the first time that IL-5 priming of opsonized particle-induced responses is mediated by tyrosine kinase activity in human eosinophils.

The Human Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF ) Receptor Exists as a Preformed Receptor Complex That Can Be Activated by GM-CSF, Interleukin-3, or Interleukin-5

The granulocyte-macrophage colony-stimulating factor (GM-CSF ) receptor is expressed on normal and malignant hematopoietic cells as well as on cells from other organs in which it transduces a variety of functions. Despite the widespread expression and pleiotropic nature of the GM-CSF receptor, little is known about its assembly and activation mechanism. Using a combination of biochemical and functional approaches, we have found that the human GM-CSF receptor exists as an inducible complex, analogous to the interleukin-3 (IL-3) receptor, and also as a preformed complex, unlike the IL-3 receptor or indeed other members of the cytokine receptor superfamily. We found that monoclonal antibodies to the GM-CSF receptor α chain (GMRα) and to the common β chain of the GM-CSF, IL-3, and IL-5 receptors (βc ) immunoprecipitated both GMRα and βc from the surface of primary myeloid cells, myeloid cell lines, and transfected cells in the absence of GM-CSF. Further association of the two chains could be induced by the addition of GM-CSF. The preformed complex required only the extracellular regions of GMRα and βc , as shown by the ability of soluble βc to associate with membrane-anchored GMRα or soluble GMRα. Kinetic experiments on eosinophils and monocytes with radiolabeled GM-CSF, IL-3, and IL-5 showed association characteristics unique to GM-CSF. Significantly, receptor phosphorylation experiments showed that not only GM-CSF but also IL-3 and IL-5 stimulated the phosphorylation of GMRα-associated βc . These results indicate a pattern of assembly of the heterodimeric GM-CSF receptor that is unique among receptors of the cytokine receptor superfamily. These results also suggest that the preformed GM-CSF receptor complex mediates the instantaneous binding of GM-CSF and is a target of phosphorylation by IL-3 and IL-5, raising the possibility that some of the biologic activities of IL-3 and IL-5 are mediated through the GM-CSF receptor complex.

Differential expression of receptors for hemopoietic growth factors on subsets of CD34+ hemopoietic cells

The production of peripheral blood cells is regulated by hemopoietic growth factors (HGF) which promote the survival of stem cells and stimulate the proliferation and maturation of progenitors as well as effector functions of mature blood cell subsets. The actions of HGF's are determined by the cellular distribution of receptors for these HGF's within the hemopoietic tissues and by the functional program that receptor-expressing cells can execute after growth factor stimulation. Identification of stem cells and their progeny and delineation of the growth factor receptor phenotype of these cells will establish target cell range and functions of individual growth factors in hemopoiesis. Cells with specific HGF receptors can be detected and isolated by flow cytometric methods, e.g., by staining with biotinylated ligand and fluorescently-tagged streptavidin. Receptor-expressing cells can be classified on the basis of expression of the CD34 antigen and other markers that distinguish immature progenitors from more differentiated cells. Using this approach distinct expression patterns have been shown for the receptors for interleukin-3 (IL-3), IL-6, granulocyte/macrophage colony-stimulating factor (GM-CSF) and Steel Factor (SF) on subsets of CD34+ and CD34- cells in bone marrow. Expression of the IL-3 receptor (R), IL-6R and GM-CSFR appears to be very low on the most immature subsets of CD34+ cells, but increases progressively during successive stages, of in particular myelomonocytic differentiation. In contrast, the receptor for SF, i.e., Kit, is highly expressed on very immature CD34-bright/HLA-DR-dull cells, which include stem cells. Kit levels decline during myelomonocytic and B-lymphoid differentiation whereas they increase to maximal levels during early stages of erythropoiesis. The heterogeneity in receptor expression, together with other immunophenotypic characteristics, allows for the identification of distinct progenitor cell subsets and differentiation stages within the CD34+ cell compartment. By selecting appropriate phenotypic criteria it will be possible to further dissect the stem cell compartment and eventually establish the, possibly heterogeneous, HGF receptor phenotype of pluripotent stem cells.

Cytokines directly induce degranulation and superoxide production from human eosinophils

BACKGROUND

Cytokines are implicated in allergic diseases and can modulate effector functions of eosinophils stimulated by another agonist. However, little is known about the capacity of cytokines to directly trigger eosinophil degranulation.

OBJECTIVES

We attempted to determine whether cytokines can directly induce degranulation and superoxide production from eosinophils.

METHODS

Eosinophils from normal donors were incubated with various cytokines in albumin-coated tissue culture plates for 4 hours. To quantitate degranulation, the amounts of eosinophil-derived neurotoxin in supernatants were measured by radioimmunoassay. In addition, superoxide production was measured by superoxide dismutase-inhibitable reduction of cytochrome c.

RESULTS

IL-5, IL-3, granulocyte-macrophage colony-stimulating factor, tumor necrosis factor- alpha, and RANTES all induced eosinophil degranulation. Granulocyte-macrophage colony-stimulating factor was the most potent and induced eosinophil-derived neurotoxin release comparable to that induced by secretory IgA beads, one of the most potent secretagogues for eosinophils. In addition, IL-5 and tumor necrosis factor- alpha were synergistic in their induction of eosinophil degranulation. In contrast, IL-1, IL-8, interferon- gamma, and macrophage inflammatory protein-1 alpha did not induce degranulation. Finally, IL-5, IL-3, granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor- alpha, but not RANTES, also induced superoxide production from eosinophils.

CONCLUSIONS

Certain cytokines directly induce eosinophil degranulation and superoxide production in vitro. Therefore these cytokines may be important in the release of toxic granule proteins from eosinophils in allergic diseases.

The direct effect of interferon-gamma on human eosinophilic leukemia cell lines: the induction of interleukin-5 mRNA and the presence of an interferon-gamma receptor

The EoL-1 and EoL-3, human eosinophilic leukemia cell lines, have been used as models for studying the maturation and the function of human eosinophils. We investigated the effects of interferon-gamma (IFN-gamma) on superoxide anion (O2-) production of these cell lines and interleukin-5 (IL-5) mRNA expression in the EoL-1. O2- was measured by chemiluminescence of MCLA, one of cypridina luciferin analogs. The O2- production of fMLP-stimulated EoL-1 and EoL-3 was increased by the IFN-gamma treatment. IL-5 mRNA expression was detected in the IFN-gamma-treated EoL-1 by reverse transcription-polymerase chain reaction (RT-PCR). Further, we examined IFN-gamma receptor 1 mRNA expression in these cell lines and peripheral blood eosinophils by means of northern blot hybridization. IFN-gamma receptor 1 mRNA was detected in the EoL-3 and the IFN-gamma-treated EoL-1. A weak expression of IFN-gamma receptor 1 mRNA was detected in peripheral blood eosinophils isolated from a patient with eosinophilia. These results suggest that IFN-gamma may act on eosinophils directly through its receptor.

Enhanced platelet recovery in myelosuppressed mice treated with interleukin-1 and macrophage colony-stimulating factor: potential interactions with cytokines having megakaryocyte colony-stimulating activity

Studies were carried out to determine whether the combination of IL-1 + M-CSF, similar to the effect of these cytokines on neutropenia, was able to reduce the duration of thrombocytopenia in the 5-fluorouracil (5-FU)-myelosuppressed mouse. In addition, comparisons were made between the in vivo effects of IL-1 + M-CSF and other "thrombopoietic" cytokines (e.g., IL-3, IL-6, and GM-CSF) that demonstrate some form of megakaryocytopoietic activity in vitro. Of the five cytokines studied, only IL-1 and IL-6, by themselves, were able to effect thrombopoietic recovery in the myelosuppressed mouse. IL-1, either when acting alone or interacting synergistically with M-CSF, was able to reduce significantly the period of thrombocytopenia, but the effects of IL-6 were restricted to enhancing platelet production during the period of rebound thrombocytopenia without altering the kinetics of thrombopoietic recovery. Moreover, none of the cytokine combinations studied were found to interact to reduce further the duration of thrombocytopenia beyond that observed with IL-1 + M-CSF. Nonetheless, IL-3, IL-6, and, to a lesser extent, GM-CSF were each able to interact with IL-1 + M-CSF to extend further the period of enhanced platelet production in the animal. However, scheduling studies suggested that these thrombopoietic cytokines interacted in sequence, rather than in concert, with IL-1 + M-CSF to enhance platelet production during thrombopoietic recovery. Furthermore, the data presented are consistent with the hypothesis that IL-1 + M-CSF initially acts on a multilineage, 5-FU-resistant target cell and that IL-6 (and possibly IL-3 and GM-CSF) serves as a secondary cytokine further to enhance platelet production during rebound thrombopoiesis in the 5-FU-treated mouse.

Differential expression of granulocyte-macrophage colony-stimulating factor and IL-3 receptor subunits on human CD34+ cells and leukemic cell lines

Cytokines transduce their signals through specific receptors. Receptors for granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-3, and IL-5 share the common signal transducing subunit (beta c), whereas the alpha subunits function as specific ligand binding components. In this study we prepared specific mouse monoclonal antibodies against human GM-CSF receptor-alpha subunit (hGMR alpha) by immunizing mice with Ba/F3 cells transfected with hGMR alpha complementary DNA. Using these anti-hGMR alpha antibodies in combination with antibodies against IL-3 receptor-alpha (IL-3R alpha), beta c subunits, and c-kit, we examined expression patterns and modulation of these receptor subunits on several human hematopoietic cells, including CD34+ cells and leukemic cell lines. GMR alpha and IL-3R alpha were expressed on GM-CSF- and IL-3-responsive cell lines, such as TF-1 and UT-7, whereas the expression levels were much lower on UT-7E, a GM-CSF- and IL-3-unresponsive subline of UT-7. The GMR alpha subunit was expressed only on mature granulocytes and monocytes, and IL-3R alpha was expressed on monocytes but not on mature granulocytes, and none of these subunits were expressed on lymphocytes. For CD34+ cells, GMR alpha was expressed more abundantly on CD34+ CD33high cells than on CD34+ CD33low cells, whereas IL-3R alpha was expressed more abundantly on CD34+ CD33low cells than on CD34+ CD33high and CD34+ CD33neg cells. Slight but significant expression of the beta c subunit was detected on CD34+ cells. Expression of not only GMR alpha and IL-3R alpha subunits but also c-kit was specifically downregulated by 48-hour incubation with their respective ligands. Receptor transmodulation between GM-CSF, IL-3, and stem cell factor (or kit ligand) was not detected on CD34+ cells in 48-hour cultures. We also detected upregulation of these alpha subunits by IL-1 alpha and interferon-gamma on leukemic cell lines. Our study showed expression levels for each receptor subunit--including GMR, IL-3R, and c-kit on human bone marrow and peripheral blood cells and leukemic cell lines--and revealed differential regulation of the expression of the receptor subunits.

Cytokines involved in growth and differentiation of human basophils and mast cells

Mast cells and basophils are multifunctional effector cells of the immune system. Both are myeloid cells and originate from multipotent hemopoietic progenitor cells. Usually, human basophils complete their differentiation in the bone marrow. In contrast, mast cells usually undergo differentiation in extramedullary organs. During the past few years, growth factors for human basophils and a growth factor for human mast cells have been identified. Interleukin-3 is the most potent differentiation factor for human basophils and activates mature basophils via high affinity binding sites. Other basophil agonists are GM-CSF, IL-5, NGF and certain chemokines (IL-8, MCP-1). Mast cells apparently loose cytokine binding sites during mastopoiesis and as mature cells, do not express detectable amounts of IL-3R, GM-CSFR or IL-8R. However, in contrast to other myeloid cells, mast cells express SCF receptor/c-kit during mastopoiesis and on mature cells. Furthermore, the ligand of c-kit, SCF, induces differentiation of human mast cells from their progenitor cells and upregulates effector functions in mature mast cells.

Identification of receptor-binding domains on human interleukin 5 and design of an interleukin 5-derived receptor antagonist

A detailed structure-function analysis of human interleukin 5 (hIL5) has been performed. The hIL5 receptor is composed of two different polypeptide chains, the alpha and beta subunits. The alpha subunit alone is sufficient for ligand binding, but association with the beta subunit leads to a 2- to 3-fold increase in binding affinity. The beta chain is shared with the receptors for IL3 and granulocyte/macrophage-colony-stimulating factor--hence the descriptor beta C (C for common). All hIL5 mutants were analyzed in a solid-phase binding assay for hIL5R alpha interaction and in a proliferation assay using IL5-dependent cell lines for receptor-complex activation. Most residues affecting binding to the receptor alpha subunit were clustered in a loop connecting beta-strand 1 and helix B (mutants H38A, K39A, and H41A), in beta-strand 2 (E89A and R91A; weaker effect for E90A) and close to the C terminus (T109A, E110A, W111S, and I112A). Mutations at one position, E13 (Glu13), caused a reduced activation of the hIL5 receptor complex. In the case of E13Q, only 0.05% bioactivity was detected on a hIL5-responsive subclone of the mouse promyelocytic cell line FDC-P1. Moreover, on hIL5-responsive TF1 cells, the same mutant was completely inactive and proved to have antagonistic properties. Interactions of this mutant with both receptor subunits were nevertheless indistinguishable from those of nonmutated hIL5 by crosslinking and Scatchard plot analysis of transfected COS-1 cells.

Structure/function analysis of human interleukin 5 and its receptor

We have performed a detailed structure-function analysis of human interleukin 5 (hIL5) and its receptor. By testing a hIL5 mutant panel in a solid phase binding assay and a proliferation assay using hIL5 dependent cell-lines, areas on hIL5 involved in either the receptor alpha-subunit interaction or in receptor activation were identified. Epitope mapping data of a neutralizing and a non-neutralizing monoclonal antibody were in agreement with the mutant analysis. hIL5 binding areas on the IL5R alpha-subunit were identified by interspecies chimaera analysis. Finally, hIL5 mutants with reduced receptor activation potential have antagonistic properties.

Recombinant human interleukin-3: pharmacokinetics after intravenous and subcutaneous bolus injection and effects on granulocyte kinetics

The pharmacokinetics of E. coli derived recombinant human interleukin-3 (rhIL-3) was studied following intravenous (i.v.) and subcutaneous (s.c.) bolus injection of rhIL-3. After i.v. bolus injection in eight patients, serum peak levels of 34.5-135.0 ng/ml were reached, followed by a rapid decline with a t1/2 alpha of 17 +/- 2 min and a t1/2 beta of 59 +/- 7 min. After s.c. bolus injection in five patients, the absorption was more prolonged with peak serum levels reached at 2.8 +/- 0.4 h. Elimination was also more protracted, and serum base-line levels were reached at 14-24 h. The immediate effect of rhIL-3 on peripheral white blood cells was less pronounced and more variable than previously found for G- or GM-CSF. Following i.v. administration, neutrophils showed a moderate drop to median 64% of initial values (range 42-85%) at median 30 min after injection (range 15-60 min) followed by an increase at 24 h to 69-288% of initial values. Eosinophils dropped to a median nadir of 34% and then gradually increased to maximum values in the range 135-720% at 18-24 h. The effect of rhIL-3 was further examined following i.v. injection of autologous 111Indium-labelled granulocytes in six patients. In steady state, i.v. injection of rhIL-3 caused a moderate drop in 111Indium activity of peripheral blood within 20 min without tendency to subsequent recovery. No change occurred in the activity recorded over the lungs and liver. The activity over the spleen decreased moderately in two patients. These results are strikingly different from those previously obtained after i.v. injection of rhGM-CSF.

Transforming growth factor beta abrogates the effects of hematopoietins on eosinophils and induces their apoptosis

Hematopoietins, interleukin (IL)-3, IL-5, and granulocyte/macrophage colony-stimulating factor (GM-CSF) have previously been shown to prolong eosinophil survival and abrogate apoptosis. The objective of this study was to investigate the effect of transforming growth factor beta (TGF-beta) on eosinophil survival and apoptosis. Eosinophils from peripheral blood of mildly eosinophilic donors were isolated to > 97% purity using discontinuous Percoll density gradient. Eosinophils were cultured with hematopoietins with or without TGF-beta for 4 d and their viability was assessed. We confirmed previous observations that hematopoietins prolonged eosinophil survival and inhibited apoptosis. TGF-beta at concentrations > or = 10(-12) M abrogated the survival-prolonging effects of hematopoietins in a dose-dependent manner and induced apoptosis as determined by DNA fragmentation in agarose gels. The effect of TGF-beta was blocked by an anti-TGF-beta antibody. The anti-TGF-beta antibody also prolonged eosinophil survival on its own. The culture of eosinophils with IL-3 and GM-CSF stimulated the synthesis of GM-CSF and IL-5, respectively, suggesting an autocrine mechanism of growth factor production. TGF-beta inhibited the synthesis of GM-CSF and IL-5 by eosinophils. TGF-beta did not have any effect on the expression of GM-CSF receptors on eosinophils. We also studied the effect of TGF-beta on eosinophil function and found that TGF-beta inhibited the release of eosinophil peroxidase. Thus, TGF-beta seems to inhibit eosinophil survival and function. The inhibition of endogenous synthesis of hematopoietins may be one mechanism by which TGF-beta blocks eosinophil survival and induces apoptosis.

The receptor for interleukin 3 is selectively induced in human endothelial cells by tumor necrosis factor alpha and potentiates interleukin 8 secretion and neutrophil transmigration

Interleukin (IL)-3 stimulates hemopoiesis in vitro. However, IL-3 is not normally found in bone marrow, raising doubts as to the in vivo role of IL-3. We have found that human umbilical vein endothelial cells (HUVEC) express functional high-affinity receptors for IL-3 after stimulation with tumor necrosis factor alpha (TNF-alpha), IL-1 beta, or lipopolysaccharide, and that this receptor is involved in inflammatory phenomena. TNF-alpha caused time- and dose-dependent up-regulation of mRNA for the IL-3 receptor alpha and beta chains, with maximal effects occurring 16-36 h after stimulation with TNF-alpha at 100 units/ml. Induction of mRNA correlated with protein expression on the cell surface as judged by monoclonal antibody staining and by the ability of HUVEC to specifically bind 125I-labeled IL-3. Scatchard analysis under optimal conditions of TNF-alpha stimulation revealed approximately 1500 IL-3 receptors per cell, which were of a high-affinity class (Kd = 500 pM) only. In contrast to a previous report, receptors for granulocyte-macrophage colony-stimulating factor could not be detected. IL-3 binding to TNF-alpha-activated HUVEC enhanced IL-8 production, E-selection expression, and neutrophil transmigration. The selective induction of a functional IL-3 receptor on endothelial cells suggests that, beyond hemopoiesis, IL-3 may have an important role in chronic inflammation and in allergic diseases.

Acute side effects of homologous interleukin-3 in rhesus monkeys

Interleukin-3 treatment of juvenile rhesus monkeys elicits a dose- and time-dependent syndrome that includes urticaria, palpable lymph nodes, splenomegaly, thrombocytopenia, anemia, vomiting, diarrhea, intestinal bleeding, edema, and arthritis, apart from a strong stimulation of hemopoiesis. Arthritis was found to occur significantly more often in animals expressing the major histocompatibility complex alleles B9 and Dr5. Histological analysis revealed an abundance of mast cells in urticaria and, to a lesser extent, in lungs and synovia of arthritic joints. Active osteoclasts were abundant in ribs and arthritic joints. Extramedullary hemopoiesis was encountered in liver, spleen, and kidneys. The spleen showed deposits of hemosiderin, and in the liver, Kupffer cells were loaded with iron, indicating enhanced turnover of hemoglobin. Lymph nodes and bone marrow showed macrophages involved in hemophagocytosis, which probably contributed to the development of anemia and thrombopenia. Biochemical parameters in sera were indicative of parenchymal liver damage, with cholestasis and increased erythrocyte destruction. The side effects were strongly reduced in monkeys subjected to total body irradiation just before interleukin-3 treatment. Histamine antagonists were not significantly effective in preventing side effects, which is explained by the perpetual stimulation of basophilic granulocytes by exogenous interleukin-3. The nature of the side effects indicates that interleukin-3 may be involved in the pathogenesis of acute type hypersensitivity reactions and arthritis.

Mechanisms of neutrophil and eosinophil accumulation in vivo

The accumulation of leukocytes into tissues is a characteristic feature of inflammatory reactions. This process is triggered by chemical signals generated in a tissue in response to an inflammatory stimulus e.g., invading microbes, other foreign organisms, allergens, or damaged tissue cells. The mechanisms involved in neutrophil and eosinophil accumulation in vivo are complex and dependent on an initial interaction between the leukocytes and the microvascular endothelial cells. This response is regulated by the coordinated expression and/or activation of leukocyte and endothelial cell adhesion molecules. The precise mechanisms that control the selective accumulation of eosinophils, as opposed to neutrophils, in certain inflammatory reactions (e.g., in IgE-mediated allergic reactions) remain unclear. This may be explained partly by the generation of eosinophil-specific inflammatory mediators and activation of selective adhesion pathways such as the VLA-4/VCAM-1 interaction. Although the neutrophil and eosinophil have distinct roles in host defense, they have been implicated in the pathogenesis of a number of inflammatory disorders. Thus, a better understanding of the events mediating and regulating neutrophil and eosinophil accumulation in vivo will be of considerable value in the development of therapeutic strategies for inflammatory disease states.

CD69 is expressed by human eosinophils activated in vivo in asthma and in vitro by cytokines

CD69 is an early activation marker for T cells and cross-linking of CD69 on platelets triggers aggregation and mediator release. Expression of a number of membrane receptors is induced on eosinophils after culture with certain cytokines. Therefore, we investigated whether cytokine-activated eosinophils expressed CD69. Unstimulated, peripheral blood eosinophils did not express CD69, as determined by immunofluorescence and flow cytometry (n = 15). CD69 expression was induced on eosinophils by granulocyte-macrophage colony-stimulating factor (GM-CSF) in a time- and dose-dependent manner. After 1 day in culture, expression was significant at concentrations of 10(-11) M and above. CD69 expression could be detected after stimulation with GM-CSF for only 1 hr, was significant after 2 hr and was sustained over 1-2 days in culture. CD69 expression was also induced by interleukin-3 (IL-3), IL-5 and interferon-gamma (IFN-gamma), but stimulation of eosinophils with platelet-activating factor (PAF) (10(-6) M) for up to 2 hr did not induce CD69 expression. Cycloheximide (10(-6) M) significantly inhibited GM-CSF-induced CD69 expression, suggesting a requirement for protein synthesis. However, unlike up-regulation of CR3 expression, GM-CSF-induced CD69 expression was not inhibited by dexamethasone. CD69 was present on eosinophils from the bronchoalveolar lavage (BAL) fluid of patients with mild asthma (5/5), suggesting that the in vitro findings may have biological relevance in vivo. Therefore, CD69 can be used as a marker of eosinophil activation by cytokines and is a candidate receptor for triggering eosinophil mediator release in the airways in asthma.

Interleukin 3 stimulates proliferation and triggers endothelial-leukocyte adhesion molecule 1 gene activation of human endothelial cells

Proliferation and functional activation of endothelial cells within a tissue site of inflammation are regulated by humoral factors released by cells, such as T lymphocytes and monocytes, infiltrating the perivascular space. In the present study we investigated the effects of interleukin 3 (IL-3), an activated T lymphocyte-derived cytokine, on cultured human umbilical vein endothelial cells (HUVEC). Proliferative activity, evaluated both by estimation of the fraction of cells in the S phase and by direct cell count demonstrated that IL-3, at the dose of 25 ng/ml, enhances more than threefold both DNA synthesis and cell proliferation above baseline control conditions. Binding studies with radioiodinated ligand demonstrated that HUVEC constitutively express a smaller number of IL-3 binding sites (approximately 99 binding sites per cell, with an apparent Kd of 149 pM). Accordingly, molecular analysis showed the presence of transcripts for both alpha and beta subunits of the IL-3 receptor. Functional activation of endothelial cells was evaluated by the expression of the endothelial-leukocyte adhesion molecule 1 (ELAM-1) transcript and by leukocyte adhesion. The ELAM-1 gene transcript was clearly detectable 4 h after IL-3 addition and started to decrease after 12 h. Moreover, IL-3-induced ELAM-1 transcription was followed by enhanced adhesion of neutrophils and CD4+ T cells to HUVEC. The findings that IL-3 can stimulate both proliferation and functional activation of endothelial cells suggest that this cytokine can be involved in sustaining the process of chronic inflammation.

Deregulation of granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor in murine macrophage cell line J774A.1

J774A.1 immortalized macrophage tumor cells display several phenotypes and functional capacities similar to that of murine peritoneal exudate macrophages (PEM). Both populations display comparable number of M-CSF receptors. Yet the number of GM-CSF receptors on J774A.1 cells is only one-fourth that of PEM (1,500 vs. 6,000 per cell). Unlike J774A.1 cells, which constitutively express c-myc transcripts, normal PEM required rMuGM-CSF for the induction of c-myc expression. Nevertheless, the growth of J774A.1 cells can be further enhanced in the presence of exogenous rMuGM-CSF, rHuM-CSF, and rMuIL-3. Treatment with either rMuIL-3 (20 ng/ml) and rHuTGF-beta 1 (1.0 ng/ml) for 24 hr at 37 degrees C, markedly enhanced the expression of GM-CSF receptors on normal PEM but not leukemic J774A.1 cells. J774A.1 cells also did not respond by autologous upregulation of GM-CSF receptors as seen in PEM following treatment with rMuGM-CSF. Treatment with either pertussis toxin (20-100 ng/ml) or H-8 (50 microM) for 24 hr led to an enhanced expression of GM-CSF receptors on J774A.1 cells in a time- and dose-dependent manner but did not result in enhanced receptor expression on normal PEM. These findings suggest that the expression of GM-CSF receptors may be regulated by mechanisms involving Gi-proteins and their downstream elements, which in turn are linked to regulatory pathways of other cytokine receptors. In J774A.1 cells, such regulatory interaction may not exist.

A model for the interaction of the GM-CSF, IL-3 and IL-5 receptors with their ligands

The high affinity receptors for GM-CSF, IL-3 and IL-5 are heterodimers consisting of a ligand-specific alpha chain and a common beta chain. These proteins are members of a family of proteins known as the "cytokine receptor family" which is characterized by the presence of a 200-residue ligand-binding module. The GM-CSF, IL-3 and IL-5 receptor alpha chains constitute a distinct subgroup and share features not found in other members of the cytokine receptor family, features which we propose to be important for their interaction with the common beta chain and for their binding of the structurally-related ligands. The growth hormone receptor is a well-characterized member of the cytokine receptor family. Based on the structure of the complex between growth hormone and its receptor, we have proposed sites of contact between the GM-CSF, IL-3 and IL-5 receptors and their cognate ligands.

A human interleukin 3 analog with increased biological and binding activities

Human interleukin 3 (IL-3) variants generated by site-directed mutagenesis were analyzed in multiple biological and binding assays to identify residues critical for IL-3 activity. Two mutants carrying substitutions in the predicted hydrophilic region within the first alpha-helix, [Ala21,Leu22]IL-3 and [Ala21,Leu22,Ala25]IL-3 showed loss of biological activity and high-affinity binding. Mutants in a second predicted hydrophilic region, [Ala44,Leu45,Ala46]IL-3 and [Ala44,Ala46]IL-3, however, showed similar biological and binding activities to wild-type IL-3. Mutations in a C-terminal hydrophilic region that overlaps the fourth predicted alpha-helix led to either loss or gain of function. IL-3 analogs [Glu104,Asp105]-, [Leu108]-, [Asn108]-, [Thr108]-, and [Ala101,Leu108]IL-3 were less active than wild-type IL-3, whereas [Ala101]IL-3 and [Val116]IL-3 were 2- to 3-fold more potent. Significantly, the double mutant [Ala101,Val116]IL-3 exhibited a 15-fold greater potency than native IL-3. Receptor binding studies showed that [Ala101,Val116]IL-3 exhibited increased binding to the high- and low-affinity receptors of monocytes. These results show the generation of an IL-3 analog with increased biological and binding activities and support a model where the C terminus of IL-3 interacts with the alpha chain of the IL-3 receptor, making this region a useful focus for the development of more potent IL-3 agonists or antagonists.

Modulation of eosinophil chemotaxis by interleukin-5

Eosinophilia and eosinophil function are regulated by cytokines such as granulocyte/macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and interleukin-5 (IL-5). We have investigated the modulatory role of IL-5 on N-formyl-methionyl-leucyl-phenylalanine (FMLP), neutrophil-activating factor (NAF/IL-8), platelet factor 4 (PF4), and cytokine-induced chemotaxis of eosinophils from normal individuals. These eosinophils show a small chemotactic response toward PF4 but not to NAF/IL-8 and FMLP. Preincubation of eosinophils with low concentrations of IL-5 caused significantly increased responses toward PF4 and induced a significant chemotactic response toward FMLP and NAF/IL-8. In marked contrast, IL-5 (or IL-3) priming of eosinophils from normal donors resulted in a strong inhibition of GM-CSF-induced chemotaxis. A similar decrease in the chemotactic response toward GM-CSF was observed in eosinophils derived from allergic asthmatic individuals. This finding suggests that the latter eosinophils may have had a prior exposure to IL-5 (or IL-3). Washing of the cells after priming did not abrogate the inhibition of the GM-CSF response. Our data indicate that at low concentrations IL-5 is an important modulator of eosinophil chemotaxis, causing selective upregulation or downregulation of chemotactic responses toward different agents.

Interleukin-3-induced up-regulation of CR3 expression on human eosinophils is inhibited by dexamethasone

Eosinophil function is regulated by several cytokines, including interleukin-3 (IL-3), IL-5 and granulocyte-macrophage colony-stimulating factor (GM-CSF). Culture of human eosinophils with IL-3 produced a marked, dose-dependent up-regulation of CR3 expression. This was maximal after 1 day in culture and dependent on protein and RNA synthesis, as demonstrated by inhibition with cycloheximide and actinomycin D, respectively. IL-5 and GM-CSF had a similar effect on eosinophil complement receptor type 3 (CR3) expression, but the maximal response to IL-5 was always less than to IL-3 or GM-CSF. Dexamethasone inhibited the Il-3-induced up-regulation of CR3 expression in a dose-dependent manner, with an IC50 of 5 x 10(-8) M. This study demonstrates the effect of IL-3, IL-5 and GM-CSF on eosinophil CR3 expression and confirms the capacity of eosinophils to modify their phenotype through de novo protein synthesis. This process could be inhibited by physiological concentrations of glucocorticoids, thus providing an additional mechanism for their mode of action in allergic disease.

Structure-function relationships of interleukin-3. An analysis based on the function and binding characteristics of a series of interspecies chimera of gibbon and murine interleukin-3

IL-3 is a glycoprotein cytokine involved in the hematopoietic response to infectious, immunologic, and inflammatory stimuli. In addition, clinical administration of recombinant IL-3 augments recovery in states of natural and treatment-related marrow failure. IL-3 acts by binding to high affinity cell surface receptors present on hematopoietic cells. To determine the site(s) at which IL-3 binds to it receptor, we analyzed a series of interspecies chimera of the growth factor for species-specific receptor binding and biological activity. The results suggest that IL-3 binds to its receptor and triggers a proliferative stimulus through two noncontiguous helical domains located near the amino terminus and the carboxy terminus of the molecule. To corroborate these findings, we have also mapped the binding epitopes of 10 mAb of human or murine IL-3, and have defined four distinct epitopes. Two of these epitopes comprise the amino-terminal receptor binding domain. A third epitope corresponds to the carboxy-terminal receptor interactive domain, and the fourth epitope, apparently not involved in the interaction of IL-3 and its receptor, lies between these sites. And on the basis of sandwich immunoassays using pairs of these mAbs, the two receptor interactive regions appear to reside in close juxtaposition in the tertiary structure of the molecule. These results provide a correlation of the structure-function relationships of IL-3 that should prove useful in evaluating the details of IL-3-IL-3 receptor interaction and in the rational design of clinically useful derivatives of this growth factor.

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.

Cytokine-induced (interleukins-3, -6 and -8 and tumour necrosis factor-beta) activation and deactivation of human neutrophils

The effect of various cytokines [interleukin-3(IL-3), IL-6, IL-8, tumour necrosis factor-beta (TNF-beta)] on human neutrophils (PMN) was analysed with regard to the generation of leukotrienes and the involvement of guanosine triphosphate (GTP)-binding proteins (G proteins). Incubation of cytochalasin B-pretreated PMN with cytokines alone did not lead to a generation of leukotrienes. However, the cytokines affected the formyl-methionyl-leucyl-phenylalanine-(FMLP)-induced formation of leukotrienes in a time-dependent manner. Preincubation of the cells with the different cytokines for short periods (15 seconds at 37 degrees) enhanced the subsequent FMLP-induced leukotriene generation, whereas preincubation for prolonged times resulted in a reduced formation of leukotrienes. These results correlated with the respective G protein-associated guanosine triphosphatase (GTPase) activities within isolated membrane fractions. The present study indicates a modulation of the FMLP-induced leukotriene formation by diverse cytokines via interaction with the GTP-binding proteins.

Structure-function relationships of the hematopoietic growth factors

The hematopoietic growth factors are a family of glycoproteins involved in the production of blood cells from their bone marrow precursors and in the activation of mature blood cells. Much has been learned about the structural features of these molecules responsible for their characteristic biological activities. Most studies have been based upon mutagenesis strategies of intact polypeptides and on epitope mapping of informative monoclonal antibodies to the growth factors. A more limited amount of physical data is available. This review will summarize these findings, highlight the growing body of evidence suggesting that many of these proteins share common evolutionary origins and structural elements, and hopefully point to the directions being taken for further investigations of these scientifically informative and clinically useful group of proteins.