Proteasomal regulation of betac signaling reveals a novel mechanism for cytokine receptor heterotypic desensitization.

IL-5, IL-3, and GM-CSF are hematopoietic cytokines that are key mediators of the allergic inflammatory response. The receptors for these three cytokines consist of a cytokine-specific alpha (Ralpha) chain and a shared common beta (betac) chain. Herein, we demonstrate that agonistic ligation of these receptor subunits rapidly induces proteasomal degradation of the betac, but not the Ralpha, cytoplasmic domain, resulting in termination of signal transduction and yielding a truncated betac isoform ligated to the Ralpha subunit. Proteasomal degradation of the betac cytoplasmic domain was also a prerequisite for endocytosis and lysosomal degradation of the ligated receptor subunits. Moreover, proteasome-dependent termination of signaling induced by one betac-engaging cytokine resulted in cellular desensitization to signal transduction by subsequent stimulation with another betac-engaging cytokine. These data provide the first evidence for ligand-dependent proteasomal degradation of the betac cytoplasmic domain, and they establish a novel mechanism for heterotypic desensitization of shared cytokine receptor signaling.

Understanding the pathogenesis of allergic asthma using mouse models.

OBJECTIVE: This paper reviews the current views of the pathogenesis of airway eosinophilic inflammation and airway hyperresponsiveness (AHR) in allergic asthma based on mouse models of the disease. The reader will also encounter new treatment strategies that have arisen as this knowledge is applied in practice. DATA SOURCES: MEDLINE searches were conducted with key words asthma, mouse model, and murine. Additional articles were identified from references in articles and book chapters. STUDY SELECTION: Original research papers and review articles from peer-reviewed journals were chosen. RESULTS: Although the mouse model does not replicate human asthma exactly, the lessons learned about the pathogenesis of allergic airway inflammation and AHR are generally applicable in humans. Type 2 T helper lymphocytes (Th2) orchestrate the inflammation and are crucial for the development of AHR. Cells and molecules involved in T cell activation (dendritic cells, T cell receptor, major histocompatibility complex molecule, and costimulatory molecules) are also vital. Besides these, no other cell or molecule could be shown to be indispensable for the establishment of the model under all experimental conditions. There are at least three pathways that lead to AHR. One is dependent on immunoglobulin E and mast cells, one on eosinophils and interleukin-5 (IL-5), and one on IL-13. Eosinophils are probably the most important effector cells of AHR. Radical methods to treat asthma have been tested in the animal model, including modifying the polarity of lymphocyte response and antagonizing IL-5. CONCLUSIONS: AHR, the hallmark of asthma, is attributable to airway inflammation ultimately mediated by helper T cells via three pathways, at least. The mouse model is also a valuable testing ground for new therapies of asthma.

Subcutaneous nodular amyloidosis: a case report and review of the literature.

Amyloidosis typically manifests with disseminated infiltration of multiple organ systems. Rarely, amyloidosis may be localized. We report a patient with localized subcutaneous nodular amyloidosis, without systemic amyloid involvement or myeloma, whose presenting symptom was multiple discrete neck nodules. Immunohistochemical analysis showed the amyloid deposits to be derived from lambda light chains. Twenty-four month follow-up showed minimal disease progression. A literature review showed only 5 reported cases of subcutaneous nodular amyloidosis. This is the first description of a patient with subcutaneous nodular amyloidosis derived from lambda light chains. HUM PATHOL 32:346-348.

Therapeutic efficacy of an anti-IL-5 monoclonal antibody delivered into the respiratory tract in a murine model of asthma.

BACKGROUND: IL-5 is central to the pathogenesis of airway eosinophilic inflammation and hyperresponsiveness associated with both atopic and nonatopic asthma. The therapeutic potential of IL-5 antagonists in asthma is supported by the inhibition of airway eosinophilia and hyperresponsiveness in animal models receiving neutralizing anti-IL-5 mAbs intravenously or intraperitoneally. OBJECTIVE: The purpose of this study was to test the hypothesis that mAbs against IL-5 delivered by way of the respiratory tract are as effective as those delivered intraperitoneally in diminishing the pulmonary eosinophilic inflammation and airway hyperresponsiveness in a murine model of ovalbumin-induced asthma. METHODS: Ovalbumin-sensitized Balb/c mice were given an anti-IL-5 mAb delivered intranasally or an isotype-matched control mAb delivered intranasally before respiratory challenge with ovalbumin. Outcome variables included respiratory system resistance responses to methacholine, bronchoalveolar lavage fluid cellularity, and lung histopathology. RESULTS: Anti-IL-5 mAbs administered intranasally to ovalbumin-sensitized and challenged mice significantly decreased eosinophil counts in bronchoalveolar lavage fluid and lung tissue and significantly reduced airway hyperresponsiveness relative to ovalbumin-sensitized and challenged mice that received either no mAb treatment or an isotype-matched control mAb. Similar results were obtained when an anti-IL-5 mAb was given intraperitoneally. CONCLUSION: This is the first study to demonstrate that delivery of anti-IL-5 mAbs into the respiratory tract is efficacious in attenuating the asthma phenotype in a murine model. These results provide impetus for the development of inhaled IL-5 antagonists for the treatment of human asthma.

GM-CSF, IL-5 and RANTES immunoreactivity and mRNA expression in chronic hyperplastic sinusitis with nasal polyposis (NP).

BACKGROUND: Eosinophils are a prominent feature of chronic hyperplastic sinusitis with nasal polyposis (CHS/NP). Our previous studies showed that their presence was associated with the expression of GM-CSF and RANTES mRNA. In allergic NP, increased expression of IL-5 was also found. OBJECTIVE: We wished to examine cytokine immunoreactivity for IL-5, GM-CSF and RANTES mRNA in allergic and non-allergic NP and compare immunoreactivity with expression of cytokine mRNA by in situ hybridization. Methods NP were obtained from five allergic and eight non-allergic subjects with CHS/ NP. Middle turbinate tissue from eight normal subjects were used as controls. Cell-associated cytokine mRNA was detected by in situ hybridization (ISH). Cytokine immunoreactive cells were enumerated by immunostaining. Colocalization immunostaining was also performed to identify specific cell types producing IL-5. RESULTS: Immunostaining for GM-CSF, IL-5 and RANTES protein was increased in both allergic and non-allergic NP compared with control middle turbinates. Allergic polyps contained greater numbers of IL-5 immunoreactive cells (P = 0.01), whereas non-allergic polyps contained greater numbers of GM-CSF immunoreactive cells (P = 0.04). Immunostaining was primarily associated with inflammatory cells, but immunostaining for RANTES and, to a lesser extent GM-CSF, was also seen in the epithelium. The density of immunoreactive cells was variably correlated with cytokine mRNA+ cells (GM-CSF: R=0.56, P=0.05; IL-5: R=0.76, P=0.003; and RANTES: R=0.89, P=0.0005). Colocalization immunostaining revealed that the majority of IL-5 immunoreactive cells in both allergic and non-allergic NP were T lymphocytes. However, allergic NP contained greater numbers of IL-5+/CD3+ T lymphocytes and IL-5+ mast cells, whereas non-allergic NP contained greater numbers of IL-5+ eosinophils. CONCLUSION: We conclude that GM-CSF, IL-5 and RANTES are produced in increased amounts in both allergic and non-allergic NP. Distinguishing features of non-allergic NP include fewer numbers of CD3 T lymphocytes, fewer IL-5+/CD3+ T lymphocytes and greater numbers of IL-5+ eosinophils. These differences may suggest different mechanisms of eosinophil accumulation and activation in allergic vs non-allergic NP.

Parafalcine and bilateral convexity neurosarcoidosis mimicking meningioma: case report and review of the literature.

OBJECTIVE AND IMPORTANCE: Sarcoidosis is a granulomatous disorder of unknown origin that may rarely present solely as an intracranial tumor. Neurosarcoidosis can mimic more common disease processes, such as meningioma, glioma, or metastases. It is important to keep neurosarcoidosis in mind, both preoperatively and intraoperatively, to guide appropriate treatment. We present a case of neurosarcoidosis mimicking a parafalcine and bilateral convexity meningioma. CLINICAL PRESENTATION: A 44-year-old African-American woman was referred to our institution with a diagnosis of meningioma based on a 4-month history of headaches, decreased memory, personality changes, and decreased coordination and on the results of axial computed tomography, which revealed a parafalcine and bilateral convexity mass. INTERVENTION: Cerebral arteriography and magnetic resonance imaging were performed to better characterize the lesion for anticipated surgery. Despite corticosteroid therapy, the patient continued to have progressive symptoms and underwent surgery. Intraoperative frozen sections were consistent with neurosarcoidosis. The mass was then significantly debulked unilaterally. CONCLUSION: Laboratory studies and follow-up examinations revealed no evidence of systemic sarcoidosis. The patient received corticosteroid therapy and subsequently improved. Serial magnetic resonance imaging examinations during several months revealed decreasing tumor size.

The biology of the immune system.

Intact immunity is fundamental for survival. The human immune system has evolved with the sophisticated biologic capacity to distinguish self from nonself and for memory through the process of clonal expansion. The ability to distinguish even subtle differences from self, and among myriad antigens, is possible by the rearrangement of genes that encode immunoglobulins and T-cell receptors, as well as by the requirement for T cells to recognize antigens in the context of presentation by HLA molecules encoded within the major histocompatibility complex. Modulation of immune function initiated by antigenic stimulation and cell-cell interactions is facilitated by a plethora of soluble mediators such as cytokines. This overview of the biology of the immune system provides a framework for understanding physiologic immune responses and how lacunar defects within the immune system explain the pathogenesis of immunologic disorders. Through such understanding, potential targets can be identified for therapeutic modulation of the immune system.

Late response to allergen is associated with increased concentrations of tumor necrosis factor-alpha and IL-5 in induced sputum.

Bronchial antigen challenge of sensitized atopic patients with asthma results in an early fall in FEV1, followed in a proportion of patients by a late (4 to 24 hours) fall. The late response is accompanied by an increase in bronchial reactivity, which is widely believed to reflect local influx and degranulation of inflammatory cells, particularly eosinophils, in association with elevated local secretion of cytokines. We hypothesized that the development of a late-phase bronchoconstrictor response and airway eosinophilia after allergen challenge of sensitized atopic patients with asthma is associated with elevated induced sputum concentrations of the eosinophil-active cytokines IL-5 and granulocyte-macrophage colony-stimulating factor and the proinflammatory cytokine tumor necrosis factor-alpha. We counted inflammatory leukocytes and measured cytokine concentrations in induced sputum at baseline and 24 hours after inhalational allergen challenge of 15 atopic patients with asthma who had previously demonstrated a late response. We observed significant increases in the numbers of eosinophils and the concentrations of their granule products, eosinophil cationic protein and eosinophil peroxidase. In contrast, the numbers of neutrophils and concentrations of two of their products, myeloperoxidase and human neutrophil lipocalin, did not significantly change. The numbers of sputum eosinophils correlated with the maximal late-phase fall in FEV1. Concentrations of IL-5 and tumor necrosis factor-alpha, but not granulocyte-macrophage colony-stimulating factor, were significantly elevated after allergen challenge. We conclude that the relatively noninvasive technique of induced sputum production can be used to monitor the effect of bronchial provocation on cytokine concentrations in asthma.

Behçet's-like syndrome associated with idiopathic CD4+ T-lymphocytopenia, opportunistic infections, and a large population of TCR alpha beta+ CD4- CD8- T cells.

Herein we report a patient with Behçet's like syndrome, idiopathic CD4+ T-lymphocytopenia, opportunistic infections, and a large polyclonal population of TCR alpha beta + CD4- CD8- T cells. Microfluorimetric analysis of peripheral blood mononuclear cells revealed CD4+ T-cell counts of 10 +/- 5/mm3. The CD3+ T cells were 99% TCR alpha beta +, of which 74 +/- 5% were CD4- CD8-. No clonal populations were detected by southern analysis for T-cell receptor V beta gene rearrangements. No evidence of human immunodeficiency virus infection was present, although nocardia, candida, pneumocystis, cytomegalovirus, and herpes infections were documented. The concomitant presence of opportunistic infections and a large population of TCR alpha beta + CD4- CD8- T cells suggests a pathogenic association and an intense immune response to microbial lipid or lipoglycan antigens presented in the context of CD1 molecules. This case demonstrates the potential for idiopathic CD4+ T-lymphocytopenia to occur in Behçet's-like syndrome with lethal consequences.

Production of IL-5 and granulocyte-macrophage colony-stimulating factor by naive human mast cells activated by high-affinity IgE receptor ligation.

BACKGROUND: The late-phase allergic reaction is an eosinophilic inflammatory response that begins several hours after allergen exposure, may persist for 24 hours, and is an important pathogenic mechanism in allergic disease. OBJECTIVE: Cultured naive human mast cells were used to investigate whether mast cells are a direct source of the eosinophil-promoting cytokines IL-5, IL-3, and granulocyte-macrophage colony-stimulating factor (GM-CSF). METHODS: Naive human mast cells were derived from bone marrow mononuclear cells cultured in the presence of stem-cell factor. Cytokine message and protein production in response to high-affinity IgE receptor ligation of cultured mast cells were measured by semiquantitative polymerase chain reaction and ELISA, respectively. RESULTS: IL-5, IL-3, and GM-CSF messenger RNA increased within 2 hours of mast cell activation, with IL-5 and GM-CSF message remaining elevated for 24 hours, whereas IL-3 mRNA rapidly declined. IL-5 and GM-CSF protein were measurable 4 to 6 hours after stimulation and peaked by 24 and 12 hours, respectively. IL-3 protein was not detectable. CONCLUSION: These findings demonstrate that naive mast cells do not constitutively produce IL-5 or GM-CSF protein but are a major source of these eosinophilotropic cytokines on high-affinity IgE receptor ligation.

Engineering of a functional interleukin-5 monomer: a paradigm for redesigning helical bundle cytokines with therapeutic potential in allergy and asthma.

Interleukin (IL) 5 specifically induces the differentiation of eosinophils which are central to the pathogenesis of allergies and asthma. Structurally, IL-5 is a unique member of the short-chain helical bundle subfamily of cytokines. In contrast to other subfamily members which fold unimolecularly into a single helical bundle, IL-5 forms a pair of helical bundles by the interdigitation of two identical monomers covalently linked by a pair of intermolecular disulfide bonds. Although a native IL-5 monomer lacks bioactivity, we recently reported the engineering of an insertional mutant of IL-5 (designated mono5) which folds unimolecularly into a single helical bundle and has biological activity similar to that of native IL-5. Here we demonstrate no differences in signal transduction pathways utilized by mono5 and IL-5, as determined by western blot analysis of early tyrosine phosphorylation events, Jak2 activation, and mitogen-activated protein kinase activation. However, binding studies utilizing conformationally dependent neutralizing anti-IL-5 monoclonal antibodies localized a tertiary structural perturbation near the insert of mono5. This perturbation enabled localization of a limited region of the tertiary structure of IL-5 that engages the IL-5 receptor alpha-chain. Fluorescent labeling studies further revealed that the cysteines of mono5 contained free sulfhydryl groups, thereby demonstrating that the role of the disulfide bonds of IL-5 is the structural maintenance of other functional domains. The retention of conformation epitopes by mono5, but not IL-5, under reducing conditions and the equivalent thermostability of mono5 and IL-5 despite the absence of a disulfide bond in mono5 indicated that the conformation assumed by mono5 is very stable. In addition to providing the structural framework for designing novel IL-5 agonists and antagonists, the knowledge gained from the development of mono5 will enable other helical bundle proteins to be redesigned with therapeutic potential.

Delineation of IL-5 domains predicted to engage the IL-5 receptor complex.

IL-5 is an interdigitating homodimeric glycoprotein and a member of the helical bundle family of cytokines. IL-5 is a potent activator of eosinophils and a specific promoter of their differentiation. This activity has implicated IL-5 in the pathogenesis of asthma and allergic disease. A detailed understanding of IL-5 structure and function is required to develop immunomodulators of IL-5-mediated inflammatory responses. We generated a panel of neutralizing anti-IL-5 mAbs which were used to map functional domains on IL-5. In addition, the nucleotide sequences for human IL-5, murine IL-5, rat IL-5, and eight human/murine IL-5 chimeras were engineered and expressed in COS-7 cells. These recombinant cytokines and mAbs were used in TF-1 bioassays to identify five functional epitopes on the tertiary structure of IL-5. Residues responsible for the species-specific activity of human IL-5 were identified with the murine BCL1 bioassay. One set of epitopes cluster around the helix A-loop 2 region, which is predicted to engage the IL-5 receptor beta-chain. The second set of epitopes as well as the species specificity domain cluster around the loop 3-helix D region, which is predicted to engage the IL-5 receptor alpha-chain. Together, these analyses target the A/D helical face of IL-5 as the region involved in receptor engagement.

Human B cells express IL-5 receptor messenger ribonucleic acid and respond to IL-5 with enhanced IgM production after mitogenic stimulation with Moraxella catarrhalis.

The potential for IL-5 to regulate human B cells is controversial despite its well established role as a regulatory factor for murine B cells. We hypothesized that the mechanism by which human B cells were stimulated would, as with murine B cells, determine their potential to respond to IL-5. Since Staphylococcus aureus Cowan strain I (SAC) and Moraxella catarrhalis (MCat) stimulate human B cells by distinct interactions with cell-surface Ig, we compared their potential to induce an IL-5-responsive state by human B cells purified to homogeneity. Neither SAC alone nor SAC plus IL-5 stimulated Ig production, although microgram quantities of IgM were produced with SAC plus IL-2. In contrast, MCat induced microgram quantities of IgM by B cells in the absence of exogenous cytokines, and IL-5 significantly increased IgM production over twofold in the majority of donors. Synergism of IL-5 and IL-2 was detected using suboptimal concentrations of IL-2 with MCat-, but not SAC-, stimulated B cells. Donor B cells unresponsive to IL-5 when stimulated with MCat, became IL-5 responsive in the presence of IL-2. Since message for the IL-5R alpha, IL-5R beta, and soluble IL-5R alpha chains was detected in freshly isolated B cells, we further investigated whether IL-5 responsiveness to MCat, but not SAC, was due to their differential regulation of IL-5R mRNA. Surprisingly, stimulation by either MCat or SAC, without or with IL-2, increased both IL-5R alpha and IL-5R beta mRNA and decreased soluble IL-5R alpha mRNA. These studies demonstrate that, as with murine B cells, human B cells express message for IL-5R but can respond to IL-5 only if appropriately stimulated to undergo terminal differentiation.

Creation of a biologically active interleukin-5 monomer.

Interleukin-5 (IL-5) specifically induces the differentiation of eosinophils, which are important in host defence and the pathogenesis of allergies and asthma. Structurally, IL-5 is a unique member of the short-chain helical-bundle subfamily of cytokines whose canonical motif contains four helices (A-D) arranged in an up-up-down-down topology. In contrast to other subfamily members, which fold unimolecularly into a single helical bundle, IL-5 forms a pair of helical bundles by the interdigitation of two identical monomers that contribute a D helix to the other's A-C helices. We predicted that the lack of bioactivity by an IL-5 monomer was due to a short loop between helices C and D which physically prevents unimolecular folding of helix D into a functionally obligate structural motif. Here we report that, by lengthening this loop, we have engineered an insertional mutant of IL-5 that was expressed as a monomer with biological activity similar to that of native IL-5. These studies demonstrate that all of the structural features necessary for IL-5 to function are contained within a single helical bundle.

Versatile E. coli thioredoxin specific monoclonal antibodies afford convenient analysis and purification of prokaryote expressed soluble fusion protein.

A recently developed E. coli thioredoxin (Trx) gene fusion expression system has circumvented the difficulties associated with inclusion body formation. Although ample quantities of soluble recombinant protein can be expressed using this system, no universal means of quantifying or purifying the fusion product exists. To facilitate the study of Trx fusion proteins, anti-E. coli Trx monoclonal antibodies (mAb) were generated. Two distinct Trx epitopes were defined by competitive ELISA. Both mAb were capable of detecting Trx fusion proteins by sandwich ELISA, and by immunoblot analysis under reducing and non-reducing conditions. In addition, these mAb enabled purification of Trx fusion proteins by immunoprecipitation, as well as affinity chromatography. This report provides the first description of anti-Trx antibodies. These reagents represent a major advance in the isolation and analysis of prokaryote expressed recombinant Trx fusion proteins.

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.

Natural killer cell suppression of IgM production.

The mechanisms by which natural killer (NK) cells regulate B cell function are not well understood. In this paper, the suppressive effects of NK cells on IgM production by lipopolysaccharide (LPS)-stimulated B cells were studied. We found that interleukin (IL)-2-activated NK (NKa) cells, but not unstimulated NK cells, suppressed IgM production by B cells stimulated with LPS. Suppression of antibody production required direct NKa-B cell contact, as demonstrated in cultures utilizing semiporous membranes for cell separation, and was the consequence of a reduction in the number of IgM-producing cells, as determined by enzyme-linked immunospot assays. Suppression could not be accounted for by cytotoxic mechanisms since the NKa cells caused neither cytolysis of 51Cr-labelled B cells or B cell apoptosis. While NKa-B cell contact was necessary for suppression, cell contact alone was not sufficient. Rather, both NKa-B cell contact and NKa production of interferon (IFN)-gamma were necessary. Since only IL-2-activated, but not unstimulated, NK cells suppressed IgM production, we investigated the potential for IL-4, which has been reported to downregulate IL-2-induced NK cell proliferation, to prevent NKa cell suppressive activity. While IL-4 antagonized IL-2-induced NK cell proliferation, it was completely ineffective in antagonizing NKa cell suppression of IgM production. The requirement for IL-2 activation of NK cells for suppression of IgM production suggests that NK cells may be part of a physiologic negative feedback mechanism to downregulate antibody production.