An interleukin (IL)-13 receptor lacking the cytoplasmic domain fails to transduce IL-13-induced signals and inhibits responses to IL-4

Artificial DnaJ Protein for protein production and conformational diseases

For secreted proteins, proper protein folding is essential not only for biological function but also for secretion itself. Proteins with folding problems are trapped in the endoplasmic reticulum (ER) and are eventually degraded in the cytoplasm. In this study, we exploited co-expression of an artificial fusion protein, based on the sequence of a DnaJ protein, which could interact as co-chaperones in the Hsp70-based protein-folding system, with target recombinant secreted proteins to enhance their production and secretion. The J-domain sequence or a fragment thereof was conjugated to a target protein–binding domain that was capable of binding to a portion of the target-protein sequence. Production of many of the target proteins was significantly upregulated when co-expressed with the J-domain fusion protein. Surprisingly, the enhancement of secretion was observed even when the J-domain had a mutation in the HPD motif, which is necessary for J-protein–Hsp70 interactions, suggesting the phenomenon observed is independent on functional J-protein–Hsp70 interactions. This technology has great potential for not only enhancing the production of recombinant proteins, but also to treat conformational diseases such as cystic fibrosis, and Alpha-1 antitrypsin deficiency.

Neuroimmunology of the Interleukins 13 and 4

The cytokines interleukin 13 and 4 share a common heterodimeric receptor and are important modulators of peripheral allergic reactions. Produced primarily by T-helper type 2 lymphocytes, they are typically considered as anti-inflammatory cytokines because they can downregulate the synthesis of T-helper type 1 pro-inflammatory cytokines. Their presence and role in the brain is only beginning to be investigated and the data collected so far shows that these molecules can be produced by microglial cells and possibly by neurons. Attention has so far been given to the possible role of these molecules in neurodegeneration. Both neuroprotective or neurotoxic effects have been proposed based on evidence that interleukin 13 and 4 can reduce inflammation by promoting the M2 microglia phenotype and contributing to the death of microglia M1 phenotype, or by potentiating the effects of oxidative stress on neurons during neuro-inflammation. Remarkably, the heterodimeric subunit IL-13Rα1 of their common receptor was recently demonstrated in dopaminergic neurons of the ventral tegmental area and the substantia nigra pars compacta, suggesting the possibility that both cytokines may affect the activity of these neurons regulating reward, mood, and motor coordination. In mice and man, the gene encoding for IL-13Rα1 is expressed on the X chromosome within the PARK12 region of susceptibility to Parkinson’s disease (PD). This, together with finding that IL-13Rα1 contributes to loss of dopaminergic neurons during inflammation, indicates the possibility that these cytokines may contribute to the etiology or the progression of PD.

Association of IL13R alpha 1 +1398A/G polymorphism in a North Indian population with asthma: A case-control study

Background:

Interleukin 13 (IL13) is directly involved in the secretion of total serum immunoglobulin E (IgE), which plays a major role in the asthma pathogenesis.

Objective:

One of the polymorphic receptor of IL13 is IL13Rα1, which after binding to IL13, initiates signal transduction that results in mucin secretion, airway hyperreactivity, fibrosis, and chitinase up-regulation, which increases asthma risk.

Methods:

In the present study, the role of IL13Rα1 +1398A/G gene polymorphisms in asthma was detected with a total of 964 individuals, including 483 healthy controls and 481 asthma patients from a North Indian population using polymerase chain reaction-restriction fragment length polymorphism method.

Results:

Statistical analysis revealed that the mutant allele (G) is predominant in asthma patients (42.7%) than the controls (38.2%), which shows an increased risk toward asthma with odds ratio = 1.21, 95% confidence interval (1.00–1.45), χ² = 4.10 and p = 0.043. Furthermore, the phenotypic characteristics also reveal a significant association with the disease (p < 0.05).

Conclusions:

This is the first study conducted in India and +1398A/G polymorphism in noncoding region of IL13Rα1 confer risk toward asthma in the studied population.

The potential for genetically altered microglia to influence glioma treatment

Diffuse and unstoppable infiltration of brain and spinal cord tissue by neoplastic glial cells is the single most important therapeutic problem posed by the common glioma group of tumors: astrocytoma, oligoastrocytoma, oligodendroglioma, their malignant variants and glioblastoma. These neoplasms account for more than two thirds of all malignant central nervous system tumors. However, most glioma research focuses on an examination of the tumor cells rather than on host-specific, tumor micro-environmental cells and factors. This can explain why existing diffuse glioma therapies fail and why these tumors have remained incurable. Thus, there is a great need for innovation. We describe a novel strategy for the development of a more effective treatment of diffuse glioma. Our approach centers on gaining control over the behavior of the microglia, the defense cells of the CNS, which are manipulated by malignant glioma and support its growth. Armoring microglia against the influences from glioma is one of our research goals. We further discuss how microglia precursors may be genetically enhanced to track down infiltrating glioma cells.

IL-13Rα1 is a surface marker for M2 macrophages influencing their differentiation and function

In this study, we examined the role IL-13 receptor alpha 1 (IL-13Rα1) plays in macrophage differentiation and function. The findings indicate that IL-13Rα1 is expressed on the M2 but not on the M1 subset of macrophages and specifically heterodimerizes with the IL-4Rα chain to form a type II receptor, which controls the differentiation and function of these cells. Indeed, BM cells from IL-13Rα1(+/+) and IL-13Rα1(-/-) mice yield equivalent numbers of macrophages when cultured under M2 polarizing conditions. However, IL-13Rα1(-/-) BM cells yield a much higher number of macrophages than IL-13Rα1(+/+) BM cells when the differentiation is carried out under M1-polarizing conditions. Further analyses indicated that macrophages that express IL-13Rα1 also display surface markers associated with an M2 phenotype. In addition, the IL-13Rα1(+) macrophages were highly efficient in phagocytizing zymosan bioparticles both in vitro and in vivo, and supported differentiation of naïve T cells to a Th2 phenotype. Finally, when stimulated by IL-13, a cytokine that uses the heteroreceptor, the cells were able to phosphorylate STAT6 efficiently. These previously unrecognized findings indicate that IL-13Rα1 serves as a marker for M2 macrophages and the resulting heteroreceptor influences both their differentiation and function.

Gene-gene interactions between candidate gene polymorphisms are associated with total IgE levels in Korean children with asthma

OBJECTIVE

To investigate associations between total serum immunoglobulin E (IgE) levels and single nucleotide polymorphisms (SNPs) from eight candidate genes (IL-4 rs2243250, IL-4Rα rs1805010, IL-13 rs20541, IL-13Rα1 rs2495636, CD14 rs2569190, tumor necrosis factor-alpha (TNF-α) rs1800629, cytotoxic T lymphocyte-associated antigen (CTLA4) rs231775, FCER1B rs1441585) in children with asthma and to evaluate gene-gene interactions.

METHODS

A total of 669 Korean children with asthma (n = 544 atopic n = 125 non-atopic) were included. Asthma phenotypes, total serum IgE levels, and methacholine challenge test results were evaluated. SNPs were genotyped using the polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP) method. Multi-factor dimensionality reduction (MDR) was used to analyze gene-gene interactions.

RESULTS

The combination of the IL-13, IL-13Rα1, and CTLA4 polymorphisms was selected through MDR analysis of the data pertaining to children with atopic and non-atopic asthma (accuracy = 0.5459, cross validation consistency (CVC) = 10/10). The IL-4Rα, IL-13, IL-13Rα1, CD14, and CTLA4 polymorphisms were selected as the best model of increased total serum IgE levels in non-atopic and atopic asthma (asthma: accuracy = 0.4726, CVC = 10/10; atopic asthma: accuracy = 0.4573, CVC = 10/10). Both the IL-4Rα and the IL-13 polymorphisms were correlated with the IgE level. ANOVA analysis revealed that the combinations of the CTLA4 and IL-13, IL-13 and IL-13Rα1, IL-4Rα and IL-13, and CD14 and IL-13 polymorphisms were all significantly associated with increased total serum IgE levels.

CONCLUSIONS

The best model of increased IgE level included the IL-4Rα, IL-13, IL-13Rα1, CD14, and CTLA4 polymorphisms. Of the various interactions between these polymorphisms, the combinations of the CTLA4 and IL-13 polymorphisms and the IL-13 and IL-13Rα1 polymorphisms showed synergistic effects in terms of increased total serum IgE levels in the present cohort.

Increased T-cell survival by structural bronchial cells derived from asthmatic subjects cultured in an engineered human mucosa

BACKGROUND

Interaction between lymphocytes and structural cells has been proposed as a key factor in regulating inflammation in asthma.

OBJECTIVE

This study was designed to investigate the effect of epithelial cells and fibroblasts on T-lymphocyte survival by using a 3-dimensional tissue-engineered model.

METHODS

Engineered human bronchial mucosal tissues were produced by using fibroblasts, epithelial cells, and autologous T cells from asthmatic and healthy donors. T-cell apoptosis and apoptotic marker expression by T cells were evaluated by using the terminal deoxynucleotidyl transferase biotinylated d-UTP nick end-labeling technique and immunofluorescence, respectively. Cytokines implicated in T-cell survival were measured by means of ELISA in culture supernatants.

RESULTS

We demonstrated histologically that we were able to generate a well-structured engineered bronchial mucosa by using epithelial cells, fibroblasts, and T cells cultured from healthy and asthmatic subjects. Structural cells from asthmatic subjects cultured in this model induced a significant decrease in the ability of T cells to undergo apoptosis represented by a decrease in DNA fragmentation and proapoptotic molecule expression (Bcl-2-associated X protein and Fas ligand). Structural cells from healthy control subjects have no effect. Among cytokines measured in the supernatants, only TGF-beta(1) was significantly increased in the model derived from cells of asthmatic subjects.

CONCLUSION

These results support the concept that bronchial structural cells might play a critical role in the regulation of inflammation in asthma by increasing the survival of T lymphocytes. The results also further validated the model as a tool for investigating the interaction between inflammatory and structural cells.

Expression of human IL-13 receptor α2 extracellular domain in Pichia pastoris

Interleukin-13 receptor alpha2 (IL-13Ralpha2) binds IL-13 with high affinity and plays an important role in IL-13 signaling as a decoy receptor. We expressed the extracellular domain of human IL-13Ralpha2 (1-313) in methylotrophic yeast Pichia pastoris. SDS-PAGE analysis by PAS staining and Western blot analysis detected the product of the extracellular domain of human IL-13Ralpha2 as glycoprotein from P. pastoris. The yield of purified extracellular domain of human IL-13Ralpha2 was 2mg from 1L of culture. From CD analysis, the 2D structure of the purified IL-13Ralpha2 showed the typical beta-sheet. ELISA of the purified IL-13Ralpha2 detected the binding activity for human IL-13. Thus, it was found that the active extracellular domain of human IL-13Ralpha2 was expressed from P. pastoris.

Gene-gene interaction between IL-13 and IL-13Ralpha1 is associated with total IgE in Korean children with atopic asthma

Interleukin (IL)-13, which is essential for IgE synthesis, mediates its effects by binding with a receptor composed of IL-4Ralpha and IL-13Ralpha1. We investigated the effects of IL-13 and IL-13Ralpha1 polymorphisms in Korean children with asthma, and whether these have been associated with IgE production. We enrolled 358 atopic asthmatic, 111 non-atopic asthmatic, and 146 non-atopic healthy children. IL-13 and IL-13Ralpha1 genotypes were identified using the PCR-RFLP method. There was an association between the asthma susceptibility and homozygosity for risk allele of IL-13 G+2044A. In children with atopic asthma, risk alleles in IL-13 (A-1512C and C-1112T) and IL-13Ralpha1 (A+1398G) showed increased total IgE (P=0.012, 0.015 and 0.017, respectively). Three-loci haplotype analysis for IL-13 showed that the haplotype composed of -1512C, -1112T and +2044A was associated with higher total IgE than other tested haplotypes in children with atopic asthma (P=0.003). The gene-gene interaction between risk alleles of each IL-13 promoter polymorphism and IL-13Ralpha1 polymorphism was associated with higher total IgE in children with atopic asthma (P=0.002, 0.010). These findings indicate that the IL-13 G+2044A is associated with asthma development and the IL-13 and IL-13Ralpha1 polymorphisms may interact to enhance IgE production.

Asthma: pathology and pathophysiology

CONTEXT

Asthma has been defined as a chronic inflammatory disorder of the airways that is associated with recruitment of inflammatory cells and the clinical development of wheezing, shortness of breath, chest tightness, and cough. Asthma is a major public health issue. It affects 5% of the United States population and accounts for 2 million emergency department visits, 470,000 hospitalizations, and 4500 deaths annually.

OBJECTIVE

To review the pathophysiology and characteristic pathologic patterns of this disease and discuss the possible mechanisms of production of the lesions.

DATA SOURCES

We searched the literature using MEDLINE and OVID. We also searched related conference abstracts and bibliographies of selected studies.

CONCLUSIONS

There has been a significant evolution in our understanding of asthma. Specific pathways and mechanisms in recent years have been studied; however, numerous mediators and cell receptors have raised new questions that remain to be answered.

Regulation of antigen-specific versus by-stander IgE production after antigen sensitization

IgE is critical in the pathogenesis of allergic disorders. In this report, we investigated the differential regulation of antigen-specific and by-stander IgE. Ovalbumin (OVA) immunization did not increase IgE producing cells in the spleen, but significantly enhanced the intracellular IgE content of all IgE+ cells. In contrast, OVA induced a significant increase of IgE+ cells in the draining lymph nodes (LN). Furthermore, OVA-specific IgE was detected only in the ex vivo cultures of the draining LN but not the spleen cells, while total IgE was increased in both cultures. These results indicated that antigen-specific IgE was mainly produced in the draining LN, while the spleen was a major source for by-stander IgE. Anti-IL-4, but not anti-IL-13, antibody blocked the expansion of IgE producing cells in the draining LN as well as systemic OVA-specific and total IgE levels, indicating IL-4 was important in both antigen-specific IgE generation and total IgE upregulation.

STAT-1 is activated by IL-4 and IL-13 in multiple cell types

While interleukin-4 (IL-4) and interleukin-13 (IL-13) can utilize a common receptor, composed of IL-4Ralpha and IL-13Ralpha1, IL-4 can also signal through a receptor with IL-4Ralpha and the common gamma chain (gammaC) as its subunits. IL-4 and IL-13 have been reported to elicit similar biological effects in a number of settings, including stimulating Ig isotype switching to IgE and inducing chemokines and cytokines in a variety of cell types whereas, depending on the receptor expression on responder cells, differential effects such as induction of type II helper T cell differentiation by IL-4 but not by IL-13 are also well documented. Recent data suggest distinct roles for these two cytokines in the 'in vivo' pathology of airway inflammatory diseases such as asthma. In this study, we examined the possibility of differential signaling by IL-4 and IL-13 on cells of the airway, by comparing expression of receptor chains and activation of different Signal Transducer and Activator of Transcription (STAT) family members. Five primary cultured cell lines representing four non-immune human lung tissue cell types (smooth muscle, epithelium, endothelium, and fibroblast) were utilized. While we readily detected expression of IL-4 Ralpha and IL-13Ralpha1 in all five cell lines, gammaC was not detectable in any of these cell lines. Consistent with previous reports, we detected STAT-6 activation in all five airway tissue cell lines examined in response to both cytokines. In addition, we also consistently detected STAT-1 activation in all of these cells. This observation was extended to include lymphoid as well as myeloid cells that express also gammaC chain. In conclusion, while the study found no differences in STAT activation in response to the two cytokines, the data show that in addition to STAT-6 activation, STAT-1 activation is also a part of the integral signaling pathways utilized by IL-4 and IL-13.

Insulin receptor substrate-2-dependent interleukin-4 signaling in macrophages is impaired in two models of type 2 diabetes mellitus

We have shown previously that hyperinsulinemia inhibits interferon-alpha-dependent activation of phosphatidylinositol 3-kinase (PI3-kinase) through mammalian target of rapamycin (mTOR)-induced serine phosphorylation of insulin receptor substrate (IRS)-1. Here we report that chronic insulin and high glucose synergistically inhibit interleukin (IL)-4-dependent activation of PI3-kinase in macrophages via the mTOR pathway. Resident peritoneal macrophages (PerMPhis) from diabetic (db/db) mice showed a 44% reduction in IRS-2-associated PI3-kinase activity stimulated by IL-4 compared with PerMPhis from heterozygote (db/+) control mice. IRS-2 from db/db mouse PerMPhis also showed a 78% increase in Ser/Thr-Pro motif phosphorylation without a difference in IRS-2 mass. To investigate the mechanism of this PI3-kinase inhibition, 12-O-tetradecanoylphorbol-13-acetate-matured U937 cells were treated chronically with insulin (1 nm, 18 h) and high glucose (4.5 g/liter, 48 h). In these cells, IL-4-stimulated IRS-2-associated PI3-kinase activity was reduced by 37.5%. Importantly, chronic insulin or high glucose alone did not impact IL-4-activated IRS-2-associated PI3-kinase. Chronic insulin + high glucose did reduce IL-4-dependent IRS-2 tyrosine phosphorylation and p85 association by 54 and 37%, respectively, but did not effect IL-4-activated JAK/STAT signaling. When IRS-2 Ser/Thr-Pro motif phosphorylation was examined, chronic insulin + high glucose resulted in a 92% increase in IRS-2 Ser/Thr-Pro motif phosphorylation without a change in IRS-2 mass. Pretreatment of matured U937 cells with rapamycin blocked chronic insulin + high glucose-dependent IRS-2 Ser/Thr-Pro motif phosphorylation and restored IL-4-dependent IRS-2-associated PI3-kinase activity. Taken together these results indicate that IRS-2-dependent IL-4 signaling in macrophages is impaired in models of type 2 diabetes mellitus through a mechanism that relies on insulin/glucose-dependent Ser/Thr-Pro motif serine phosphorylation mediated by the mTOR pathway.

Biology and therapeutic potential of the interleukin-4/interleukin-13 signaling pathway in asthma

The future management of patients with allergic asthma is poised to change in the coming one to two decades. This prediction is based on fundamental new insights into the pathogenesis of disease, gained through the study of both humans and experimental models of asthma. These studies have revealed that allergic asthma is an immune-mediated disease which, despite the redundancy characteristic of all immune responses, may be induced through a single dominant signaling cascade called the interleukin (IL)-4/IL-13 signaling pathway. In addition to the cytokine IL-4, this pathway includes IL-13, the cytokine receptor subunit IL-4 receptor alpha (IL-4Ralpha), Janus-associated tyrosine kinases and the transcription factor, signal transducer and activator of transcription 6. The IL-4 signaling pathway controls the most important cellular developmental (afferent) events that underlie asthma. These include T helper (Th) type 2 cell activation, B cell activation and immunoglobulin (Ig) E secretion, mast cell development, and effector (efferent) events related exclusively to immune effects on the lung such as goblet cell metaplasia and airway hyperresponsiveness. Any of the IL-4 signaling molecules are potentially amenable to pharmacological intervention, but a detailed understanding of the entire pathway is required to appreciate their actual potential for drug development. For example, neutralization strategies that target only IL-4 are unlikely to succeed because they leave IL-13 free to continue the signaling cascade. In contrast, neutralization of IL-4Ralpha may represent a more feasible strategy, as it should prevent signaling by both IL-4 and IL-13. The therapeutic potential of targeting intracytoplasmic tyrosine kinases has already been achieved with the use of small molecules, suggesting that this approach may be realistically adopted for the treatment of asthma. However, well designed asthma clinical trials are warranted to determine with certainty, the efficacy of therapies based on IL-4/IL-13 blockade.

Therapeutic attenuation of pulmonary fibrosis via targeting of IL-4- and IL-13-responsive cells

Severe forms of idiopathic interstitial pneumonia (IIP), such as usual interstitial pneumonia, can be impervious to modern steroid and immunosuppressive treatment regimens, thereby emphasizing the need for novel effective therapies. Consequently, research attention has been directed toward understanding the cytokine networks that may affect fibroblast activation and, hence, the progression of certain IIPs. This led us to investigate whether the specific targeting of resident lung cells responsive to IL-4 and IL-13 exerted a therapeutic effect in an experimental model of IIP, namely the bleomycin-induced model of pulmonary fibrosis. IL-4, IL-13, and their corresponding receptor subunits, IL-4Ralpha, IL-13Ralpha1, and IL-13Ralpha2, were maximally expressed at the mRNA and protein levels in whole lung samples on day 21 or 28 after an intratracheal bleomycin challenge. The intranasal administration of an IL-13 immunotoxin chimeric molecule (IL13-PE) from days 21-28, but not for 1-wk periods at earlier times, after bleomycin challenge had a significant therapeutic effect on histological and biochemical parameters of bleomycin-induced pulmonary fibrosis compared with the control group. The intranasal IL13-PE therapy significantly reduced the numbers of IL-4 and IL-13 receptor-positive mononuclear cells and macrophages and the levels of profibrotic cytokine and chemokine in the lungs of bleomycin-challenged mice on day 28. Thus, this study demonstrates that IL-4- and/or IL-13-binding cells are required for the maintenance of pulmonary fibrosis induced by bleomycin and highlights the importance of further investigation of antifibrotic therapeutics that target these cells during pulmonary fibrosis.

The role of interleukin-4 and interleukin-13 in the non-immunologic aspects of asthma pathogenesis

Bronchial asthma is a complex disease characterized by airway inflammation involving a Th2-cytokine, interleukin (IL)-13. A substantial body of evidence has accumulated pointing to the pivotal role of IL-13 in the pathogenesis of bronchial asthma. The evidence is categorized as (i) analyses of mouse models, (ii) expression of these cytokines in the bronchial lesions, and (iii) genetic association of the signaling molecules of these cytokines. In addition, the molecular mechanism of the signal transduction of IL-13 has also been well characterized. We have applied microarray analyses to human bronchial epithelial cultures to search for genes regulated by IL-13 and have identified a subset of disease-relevant genes by comparison with cDNA libraries derived from normal and asthmatic bronchial biopsies. Expression of squamous cell carcinoma antigen-1 (SCCA1) and SCCA2, the cysteine and serine protease inhibitors, respectively, was the highest in the bronchial epithelial cells stimulated by IL-4 and IL-13 and was augmented in the asthmatic cDNA library. Furthermore, serum levels of SCCA were also elevated in asthmatic patients. Taken together, it was supposed that SCCA may play some role in the pathogenesis of bronchial asthma, and measuring its serum level may be relevant for diagnosing or monitoring the status of bronchial asthma.

IL-13 receptors and signaling pathways: an evolving web

IL-13 is an immunoregulatory cytokine secreted predominantly by activated T(H)2 cells. Over the past several years, it has become evident that IL-13 is a key mediator in the pathogenesis of allergic inflammation. IL-13 shares many functional properties with IL-4, stemming from the fact that they share a common receptor subunit, the alpha subunit of the IL-4 receptor (IL-4Ralpha). Characterization of IL-13-deficient mice, IL-4-deficient mice, and IL-4 receptor alpha-deficient (IL-4Ralpha(-/-)) mice have demonstrated nonredundant roles for IL-13. IL-13 mediates its effects by interacting with a complex receptor system comprised of IL-4Ralpha and two IL-13 binding proteins, IL-13Ralpha1 and IL-13Ralpha2. IL-13 receptors are expressed on human B cells, basophils, eosinophils, mast cells, endothelial cells, fibroblasts, monocytes, macrophages, respiratory epithelial cells, and smooth muscle cells. However, functional IL-13 receptors have not been demonstrated on human or mouse T cells. Thus unlike IL-4, IL-13 does not appear to be important in the initial differentiation of CD4 T cells into T(H)2-type cells but rather appears to be important in the effector phase of allergic inflammation. This is further supported by many in vivo observations, including that administration of IL-13 resulted in allergic inflammation, tissue-specific overexpression of IL-13 in the lungs of transgenic mice resulted in airway inflammation and mucus hypersecretion, IL-13 blockade abolished allergic inflammation independently of IL-4, and IL-13 appears to be more important than IL-4 in mucus hypersecretion. Given the importance of IL-13 as an effector molecule, regulation at the level of its receptors might be an important mechanism of modulating IL-13 responses and thus propagation of the allergic response. Accordingly, IL-13 is an attractive, novel therapeutic target for pharmacologic intervention in allergic disorders. This review will summarize the current understanding of the IL-13 receptors and signaling pathways, emphasizing recent observations.

Emerging immune targets for the therapy of allergic asthma

Recent discoveries on the molecular and cellular basis of asthma have markedly altered our understanding of this common respiratory disorder. These insights have come during an unexplained period of rising disease incidence and severity and are now being applied to develop improved therapies. This review explores the latest advances in our understanding of the pathogenesis of allergic asthma, and provides insight into the expanding collaborations between research scientists, clinicians and the pharmaceutical industry in the race to control the asthma epidemic.

Expression of a functional IL-13Ralpha1 by rat B cells

IL-13 mediates its effects through a complex receptor system including IL-4Ralpha and a functional IL-13Ralpha1. IL-13 has been reported to have no effects on mouse B cells due to a lack of receptor expression. However, on human B cells a functional IL-13Ralpha1 has been described. Here, we identified the rat IL-13Ralpha1 in order to analyze its expression and function in rat B cells. The expression of IL-13Ralpha1 has been shown by the presence of mRNA and the corresponding protein in purified rat B cells and in rat hybridoma B cell line. Rat B cells are able to bind IL-13 and to proliferate when cultured with CD40 ligand and IL-13. In vivo experiments showed that administration of IL-13 did enhance IgE production. These results suggest a direct interaction of rat B cells with IL-13 through a functional receptor with an increase of IgE production and provide a relevant model to further study the activity of IL-13 and to better understand its role in human diseases.

Expression of interleukin 13 receptor in glioma and renal cell carcinoma: IL13Ralpha2 as a decoy receptor for IL13

Glioma and renal cell carcinoma (RCC) cells express high affinity interleukin 13 (IL13) binding sites, but only RCC cell proliferation was inhibited by IL13. Both of these two cell types are IL2-receptor (gamma)c chain-negative. We thus used these cell models to investigate the patterns of expression of IL13Ralpha1, IL13Ralpha2, and IL4Ralpha chains and the role of IL13Ralpha2 in the response to IL13. Using new specific antibodies and flow cytometry, we observed a similar surface expression of IL4Ralpha and IL13Ralpha1 chains in most RCC and glioma cells, whereas IL13Ralpha2 was only present on five of six glioma cell lines. In all glioma cell lines, the amount of IL13Ralpha2 expression was 10 to 30 times higher than that of the two other chains. Although there was no surface or intracellular expression of IL13Ralpha2, its mRNA was detected in three of seven RCC cell lines. The expression on RCC cells of IL13Ralpha2 mRNA and/or that of high-affinity IL13 binding sites is not sufficient to predict IL13Ralpha2 protein expression. Blocking experiments showed that IL4 and IL13 strongly inhibited RCC cell proliferation through a unique receptor composed of IL4Ralpha and IL13Ralpha1 chains. Using RCC cells stably transfected with IL13Ralpha2 cDNA, we showed that the overexpression of IL13Ralpha2 decreased the response to IL13 but not that to IL4. Our results demonstrate that IL13Ralpha2 acts as a decoy receptor for IL13 and that it may exert a tight regulation of IL13 activity without impairing the IL4 response of the same cell target.

A novel monoclonal antibody, C41, reveals IL-13Ralpha1 expression by murine germinal center B cells and follicular dendritic cells

Responsiveness to IL-13 involves at least two chains, IL-4Ralpha and IL-13Ralpha1. Although mouse B cells express IL-4Ralpha, little is known about their expression of IL-13Ralpha chains. To investigate this topic further, we have generated a monoclonal antibody (C41) specific for murine IL-13Ralpha1. Using C41, IL-13Ralpha1 expression was detected on germinal center (GC) B cells by flow cytometry and immunohistochemistry. In addition, IL-13Ralpha1 was observed on follicular dendritic cells, but not interdigitating dendritic cells in the T cell areas. Furthermore, resting B cells also expressed IL-13Ralpha1, and in the presence of IL-13 produced increased amounts of IgM in response to in vitro CD40 stimulation. However, C41 was unable to neutralize this bioactivity. The distribution of IL-13Ralpha1 on murine B cells and during GC reactions suggests a role for IL-13 during B cell differentiation.

Characterization of IL-4 and IL-13 signals dependent on the human IL-13 receptor alpha chain 1: redundancy of requirement of tyrosine residue for STAT3 activation

IL-4 and IL-13 are pleiotropic cytokines whose biological activities overlap with each other. IL-13 receptor alpha chain 1 (IL-13R alpha 1) is necessary for binding to IL-13, and the heterodimer composed of IL-13R alpha 1 and IL-4R alpha chain transduces IL-13 and IL-4 signals; however, the functional mapping of the intracellular domain of IL-13R alpha 1 is not fully understood. In this study, we constructed wild and mutated types of human IL-13R alpha 1, and analyzed IL-4 and IL-13 signals using an IL-13R alpha 1-transfected human B cell line. Expression of IL-13R alpha 1 evoked STAT3 activation by IL-4 and IL-13, and in stimulated human B cells, on which IL-13R alpha 1 was highly expressed, IL-4 and IL-13 induced STAT3 activation. Replacement of the two tyrosine residues completely abolished STAT3 activation, although replacing either tyrosine residue alone retained it. Furthermore, we found that the Box1 region and the C-terminal tail of IL-13R alpha 1 were critical for binding to Tyk2, and activation of Jak1, Tyk2, the insulin receptor substrate-1 and STAT6 respectively. These results suggest that STAT3 activation is involved with IL-4 and IL-13 signals in human B cells along with the activation of STAT6, and that there is a unique sequence in IL-13R alpha 1 to activate STAT3.

Augmentation of signal transducer and activation of transcription (STAT)6 and STAT3 expression in stimulated B and T cells

Signal transducer and activation of transcription (STAT)6 has a central role in the signal transduction of interleukin (IL)-4 and IL-13. It has recently been revealed that STAT3 is also involved. STAT6 and STAT3 are expressed ubiquitously; however, it remains unknown how STAT6 and STAT3 expression is regulated. In this study, we found that STAT6 expression was augmented at the transcription level in B and T cells stimulated with anti-IgM antibody and anti-CD40 antibody or PMA and ionomycin, respectively, and that STAT3 expression was similarly augmented in the stimulated B cells. The stimulated B and T cells showed enhancement of STAT6 activation and CD23 expression induced by IL-4 and IL-13. Augmentation of STAT6 and STAT3 would be a mechanism of the amplification of the IL-4 and IL-13 signals in stimulated B and T cells.

A Soluble Form of IL-13 Receptor α1 Promotes IgG2a and IgG2b Production by Murine Germinal Center B Cells

A functional IL-13R involves at least two cell surface proteins, the IL-13Rα1 and IL-4Rα. Using a soluble form of the murine IL-13Rα1 (sIL-13R), we reveal several novel features of this system. The sIL-13R promotes proliferation and augmentation of Ag-specific IgM, IgG2a, and IgG2b production by murine germinal center (GC) B cells in vitro. These effects were enhanced by CD40 signaling and were not inhibited by an anti-IL4Rα mAb, a result suggesting other ligands. In GC cell cultures, sIL-13R also promoted IL-6 production, and interestingly, sIL-13R-induced IgG2a and IgG2b augmentation was absent in GC cells isolated from IL-6-deficient mice. Furthermore, the effects of the sIL-13R molecule were inhibited in the presence of an anti-IL-13 mAb, and preincubation of GC cells with IL-13 enhanced the sIL-13R-mediated effects. When sIL-13R was injected into mice, it served as an adjuvant-promoting production to varying degrees of IgM and IgG isotypes. We thus propose that IL-13Rα1 is a molecule involved in B cell differentiation, using a mechanism that may involve regulation of IL-6-responsive elements. Taken together, our data reveal previously unknown activities as well as suggest that the ligand for the sIL-13R might be a component of the IL-13R complex or a counterstructure yet to be defined.

The role of IL-13 in helminth-induced inflammation and protective immunity against nematode infections

Helminth infections induce the production of type 2 cytokines, which contribute both to expulsion of the worms and inflammatory responses that can either protect or damage the host. Although IL-4 has been considered the most critical cytokine for both inflammation and protective immunity, recent observations indicate that IL-13 - a related cytokine - can have equal or even greater importance than IL-4 in inflammatory responses and host protection against infection.

Characterization of the cytoplasmic domain of interleukin-13 receptor-alpha

Interleukin (IL)-13 and IL-4 are pleiotropic immunoregulatory cytokines that share many overlapping biological properties reflecting the fact that both can utilize a receptor complex composed of the IL-4 receptor-alpha (IL-4Ralpha) chain and the IL-13Ralpha chain. The cytoplasmic domain of the IL-13Ralpha is 60 amino acids long and is essential for IL-13-dependent growth. It contains a Pro-rich domain in the membrane-proximal region and two Tyr residues. Here we show that a truncated IL-13Ralpha, lacking the 38 carboxyl-terminal residues but retaining the Pro-rich region, can support IL-13-dependent proliferation, although with reduced efficiency. A Y402F mutant of the cytoplasmic domain of IL-13Ralpha supported normal IL-13-induced growth. However, tyrosine phosphorylation of signal transducer and activator of transcription 3 (STAT3), which we show is induced by IL-13 and IL-4 in cells that express the IL-13Ralpha, was significantly reduced. The cytoplasmic domain of IL-13Ralpha was constitutively associated with STAT3, Tyk2, and Janus kinase 1 (JAK1). IL-13-induced tyrosine phosphorylation of IL-13Ralpha in vivo could not be detected using anti-Tyr(P) antibodies. A glutathione S-transferase fusion protein of the cytoplasmic domain of IL-13Ralpha was phosphorylated on tyrosine in vitro by JAK1, JAK3, and Tyk2, although the tyrosine phosphorylation events mediated by Tyk2 and JAK3 were not detectable using anti-phosphotyrosine antibodies. These data, together with the demonstration that IL-13Ralpha associates constitutively with Tyk2 and that Tyr-402 is involved in IL-13-induced phosphorylation of STAT3, suggest that the latter is mediated by Tyk2. Tyrosine phosphorylation of STAT3, which was not necessary for IL-13-induced proliferation, may account for some of the effects of IL-4 and IL-13 on the function of their targets.

Role of endothelin-1 and constitutive nitric oxide synthase in gastric mucosal resistance to indomethacin injury: effect of antiulcer agents

BACKGROUND

Endothelin-1 (ET-1) and nitric oxide, recognized key mediators implicated in the pathophysiology of gastric mucosal injury, are known to exert opposing effects on the inflammatory processes mediated by regulatory cytokines. In this study we investigated the mucosal expression of ET-1 and interleukin-4 (IL-4) and the activity of constitutive nitric oxide synthase (cNOS) during indomethacin-induced gastric mucosal injury and evaluated the effect of antiulcer agents, omeprazole and sucralfate, on this process.

METHODS

The experiments were conducted with groups of rats pretreated intragastrically with omeprazole (40 mg/kg), sucralfate (200 mg/kg), or vehicle, followed 30 min later by an intragastric dose of indomethacin (60 mg/kg). The animals were killed 2 h later, and their mucosal tissue subjected to macroscopic damage assessment, ET-1 and IL-4 expression assay, and the measurement of cNOS activity.

RESULTS

In the absence of antiulcer agents, indomethacin caused multiple hemorrhagic lesions and extensive epithelial cell apoptosis, accompanied by a 20.7% reduction in IL-4, a 3.1-fold increase in mucosal expression of ET-1, and a 4.2-fold decrease in cNOS. Pretreatment with a gastroprotective agent, sucralfate, produced a 59.7% reduction in the mucosal damage caused by indomethacin, a 41.2% decrease in epithelial cell apoptosis, and a 56.5% reduction in ET-1, whereas the expression of IL-4 increased by 29.3% and that of cNOS showed a 3.3-fold increase. In contrast, the pretreatment with a proton pump inhibitor, omeprazole, led to only a 10.5% reduction in the extent of mucosal damage caused by indomethacin and a 13% decrease in apoptosis, whereas the expression of cNOS increased by 68.7% and ET-1 by 12.2%, and the level of IL-4 remained essentially unchanged.

CONCLUSIONS

The results suggest that an increase in the vasoconstrictive ET-1 level combined with a decrease in regulatory cytokine, IL-4, and a loss of compensatory action by cNOS may be responsible for the gastric mucosal injury caused by indomethacin. Our findings also indicate the value of sucralfate in countering the untoward gastrointestinal side effects of nonsteroidal anti-inflammatory drug therapy.

IL-18 Is a Potent Coinducer of IL-13 in NK and T Cells: A New Potential Role for IL-18 in Modulating the Immune Response

IL-13 and IL-4 have similar biological activities and are characteristic of cytokines expressed by Th2 cells. In contrast, IL-12 and IL-18 have been shown to be strong cofactors for Th1 cell development. In this study, we found strong induction of IL-13 mRNA and protein by IL-2 + IL-18 in NK and T cells. In contrast, IL-12 did not enhance the IL-13 production induced by IL-2 alone. Moreover, IL-13 mRNA and protein expression induced by IL-2 + IL-18 in purified NK and T cells obtained from IFN-γ knockout (−/−) mice were greater than seen in purified cells from normal controls. In contrast, IL-10 production induced by IL-2 and/or IL-12 was not significantly different in IFN-γ (−/−) mice and normal controls. These results suggest IL-13 expression induced by IL-2 + IL-18 may be regulated by IFN-γ in vivo, while IL-10 expression may be IFN-γ-independent. Thus, depending upon the cell type, IL-18 may act as a strong coinducer of Th1 or Th2 cytokines. Our findings suggest that IL-12 and IL-18 have different roles in the regulation of gene expression in NK and T cells.

Antagonistic effects of an alternative splice variant of human IL-4, IL-4delta2, on IL-4 activities in human monocytes and B cells

IL-4 is a pleiotropic cytokine which exerts its actions on various lineages of hematopoietic and nonhematopoietic cells. This cytokine is one of the central regulators of immunity in health and disease states. An alternative splice variant, in which the second of four exons is omitted, has been recently described and designated as IL-4delta2. The variant has been previously described as a potential naturally occurring antagonist of human IL-4 (hIL-4)-stimulated T cell proliferation. In this study, we investigated the effects of recombinant human (rh) IL-4delta2 on monocytes and B cells. In monocytes, rhIL-4delta2 blocked inhibitory action of hIL-4 on LPS-induced cyclooxygenase-2 expression and subsequent prostaglandin E2 secretion. In B cells, rhIL-4delta2 was an antagonist of the hIL-4-induced synthesis of IgE and expression of CD23. Our results broaden the spectrum of hIL-4-antagonistic activities of rhIL-4delta2, thus creating the background for the potential use of rhIL-4delta2 as a therapeutic anti-hIL-4 agent.

Suppression of gastric mucosal inflammatory responses to Helicobacter pylori lipopolysaccharide by sulglycotide

The effect of the antiulcer agent sulglycotide on gastric epithelial cell apoptosis and the expression of tumor necrosis factor-alpha (TNF-alpha) and interleukin-4 (IL-4) during Helicobacter pylori lipopolysaccharide-induced acute gastritis was investigated. Rats, pretreated twice daily for 3 consecutive days with sulglycotide at 200 mg/kg or vehicle, were subjected to surface epithelial application of H. pylori lipopolysaccharide (50 microg/animal), and, after 4 additional days on the drug or vehicle regimen, their mucosal tissue was used for histologic assessment, quantitation of TNF-alpha and IL-4, and the assay of epithelial cell apoptosis. In the absence of sulglycotide, H. pylori lipopolysaccharide caused acute mucosal responses manifested by the inflammatory infiltration of the lamina propria with lymphocytes and plasma cells, edema, hyperemia, and epithelial hemorrhage. These responses were accompanied by an 11-fold increase in epithelial cell apoptosis and a 9-fold enhancement of the mucosal expression of proinflammatory cytokine TNF-alpha. However, the mucosal expression of regulatory cytokine IL-4 decreased by 15%. Treatment with sulglycotide produced significant (56.6%) reduction in the extent of acute mucosal inflammatory changes caused by H. pylori lipopolysaccharide. Moreover, the effect of sulglycotide was manifested in an 88.3% reduction in the epithelial cell apoptosis and a 69.1% decrease in the mucosal expression of TNF-alpha, whereas the expression of IL-4 showed only marginal (6%) enhancement. The results suggest that the cytoprotective agent sulglycotide suppresses the inflammatory and apoptotic events elicited in gastric mucosa by H. pylori lipopolysaccharide through stimulation of TNF-alpha expression.

IL-13 Production by NK Cells: IL-13-Producing NK and T Cells Are Present In Vivo in the Absence of IFN-γ

In this study, we demonstrate that human NK cells, human NK clones, the human NK cell line (NK3.3), and a population of murine NK cells can produce the type 2 cytokine IL-13 in response to IL-2 or phorbol myristate acetate plus ionomycin. IL-2 rapidly induced new IL-13 mRNA and protein synthesis in the NK3.3 cell line. Six of 12 human NK clones tested produced IL-13 protein in response to IL-2 or phorbol myristate acetate and ionomycin. Intracellular analysis revealed that ∼2% of human peripheral NK cells produced IL-13 protein in response to IL-2. Isolated NK cells from SCID and RAG-2 knockout (−/−) mice that lack T and B cells as well as normal mice also can produce IL-13 mRNA and protein in response to IL-2. We hypothesized that in the absence of IFN-γ, IL-13-producing NK cells may predominate in vivo. Utilizing IFN-γ knockout (−/−) mice as a model system, IL-2-activated liver NK and T cells expressed 10-fold more IL-13 and IL-5 mRNA and protein than normal controls following IL-2 treatment in vitro. These results suggest that in the absence of IFN-γ, an IL-13- and IL-5-producing NK and T cells predominate in vivo. The existence of this cell type has important implications in innate immunity given that the balance between IFN-γ and IL-13/IL-5-producing NK cells may influence the early development of a cell-mediated or humoral immune response.

Association of the interleukin-4 receptor alpha chain with p47phox, an activator of the phagocyte NADPH oxidase in B cells

Interleukin (IL)-4 plays an important role in IgE synthesis in B cells and in Th2 differentiation in T cells. IL-4 conducts its biological activities through binding to the IL-4 receptor (IL-4R) on the surface of target cells. IL-4R are thought to be composed of the IL-4R alpha chain (IL-4R alpha) and either the IL-2R gamma chain or the IL-13R alpha chain. We have previously shown that the membrane-proximal portion in the cytoplasmic domain of the human IL-4R alpha (hIL-4R alpha) is critical for proliferation, generation of germline epsilon transcript, and activation of STAT6, based on analyses of truncated hIL-4R alphas. In this study, we found that p47phox, an activator of the phagocyte NADPH oxidase, binds to this portion by the two-hybrid system. Furthermore, we observed the association of p47phox with the hIL-4R alpha in B cells derived from a normal donor. These results suggest that p47phox is involved in the signal transduction of IL-4 in B cells. However, activation of STAT6, CD23 expression, and IgE synthesis induced by IL-4 were not affected in p47phox-deficient patients, which raises the possibility that p47phox may be important in other signaling activities as well in B cells.

Environmental Antigen-Induced IL-13 Responses Are Elevated Among Subjects with Allergic Rhinitis, Are Independent of IL-4, and Are Inhibited by Endogenous IFN-γ Synthesis

Human immediate hypersensitivity diseases represent the most common example of chronic excessive Th2-like activation in developed nations. While IL-13 shares many functional properties with IL-4, the intensity and regulation of environmental Ag-stimulated IL-13 synthesis by allergic vs nonallergic individuals remain ill defined. Here, we examine the intensity of polyclonally and Ag-stimulated IL-13 production by PBMC of 20 subjects with seasonal allergic rhinitis and 20 healthy controls. Polyclonally driven IL-13 responses did not differ significantly (Mann-Whitney U test, p = 0.68). In contrast, the median CD4-dependent IL-13 response among atopics was markedly stronger than nonatopics in Ag-stimulated primary culture (p = 0.0031) and exhibited a strong correlation with IL-5 (r = 0.76, p = 0.0009), but not IL-4 (r = 0.14, p &gt; 0.05), responses. IL-13 production was unaffected by blocking endogenous IL-4 or IL-5 activity or by addition of rIL-4 or rIL-5. In contrast, it was inhibited by low levels of rIFN-γ and strongly enhanced upon addition of neutralizing anti-IFN-γ mAb. Collectively, the data are consistent with a negative regulatory role for endogenous IFN-γ synthesis in controlling the intensity of systemic IL-13 responses evoked in both atopic and nonatopic populations following exposure to common Ags. They also suggest that the elevated levels of IL-4 and IL-5 characteristic of type 2-dominated responses in vivo are without detectable impact on the maintenance of recall Ag-stimulated IL-13 production.

Inhibition of angiogenesis by interleukin 4

Interleukin (IL)-4, a crucial modulator of the immune system and an active antitumor agent, is also a potent inhibitor of angiogenesis. When incorporated at concentrations of 10 ng/ml or more into pellets implanted into the rat cornea or when delivered systemically to the mouse by intraperitoneal injection, IL-4 blocked the induction of corneal neovascularization by basic fibroblast growth factor. IL-4 as well as IL-13 inhibited the migration of cultured bovine or human microvascular cells, showing unusual dose-response curves that were sharply stimulatory at a concentration of 0.01 ng/ml but inhibitory over a wide range of higher concentrations. Recombinant cytokine from mouse and from human worked equally well in vitro on bovine and human endothelial cells and in vivo in the rat, showing no species specificity. IL-4 was secreted at inhibitory levels by activated murine T helper (TH0) cells and by a line of carcinoma cells whose tumorigenicity is known to be inhibited by IL-4. Its ability to cause media conditioned by these cells to be antiangiogenic suggested that the antiangiogenic activity of IL-4 may play a role in normal physiology and contribute significantly to its demonstrated antitumor activity.

Effect of sucralfate on gastric mucosal inflammatory responses induced by Helicobacter pylori lipopolysaccharide

BACKGROUND

Helicobacter pylori lipopolysaccharide is emerging as a primary factor in the bacterium virulence, and its involvement in causing gastric mucosal responses typical of gastritis has recently been shown. In this study we investigated the effect of the antiulcer agent sucralfate on the expression of regulatory cytokines, tumor necrosis factor-alpha (TNF-alpha) and interleukin-4 (IL-4), and epithelial cell apoptosis during H. pylori lipopolysaccharide-induced acute gastritis.

METHODS

The experiments were conducted with rats pretreated intragastrically twice daily for 3 days with sucralfate at 100 mg/kg or the vehicle. The rats were then subjected to intragastric surface epithelial application of H. pylori lipopolysaccharide at 50 microg per animal and maintained on the sucralfate or vehicle regimen for an additional 4 days. The animals were killed 16 h after the last dose, and their gastric mucosal tissue used for histologic assessment, quantitation of TNF-alpha and IL-4 expression, and the assay of epithelial cell apoptosis.

RESULTS

In the absence of sucralfate, H. pylori lipopolysaccharide induced acute mucosal responses characterized by the inflammatory infiltration of the lamina propria, hyperemia, and epithelial hemorrhage. This was accompanied by an 11-fold increase in gastric epithelial cell apoptosis and a 9-fold enhancement of the mucosal expression of TNF-alpha, but the level of IL-4 fell by 15%. Intragastric administration of sucralfate produced a 62% reduction in the extent of mucosal damage caused by H. pylori lipopolysaccharide, a 51% decrease in the mucosal expression of TNF-alpha, and a 7-fold reduction in the extent of epithelial cell apoptosis, whereas the expression of IL-4 increased by 52%.

CONCLUSIONS

Gastric mucosal inflammatory responses to H. pylori lipopolysaccharide are characterized by a massive enhancement of the proinflammatory cytokine TNF-alpha and epithelial cell apoptosis and repression of IL-4. Our data also show that sucralfate is capable of inducing expression of the regulatory cytokine IL-4 and the suppression of apoptotic events triggered in gastric mucosa by the increase in TNF-alpha that is elicited by H. pylori lipopolysaccharide.

Identification of the critical portions of the human IL-4 receptor alpha chain for activation of STAT6

Interleukin-4 (IL-4) has been shown to activate Janus kinase (Jak)-1 and Jak-3, followed by activation of STAT (signal transducers and activators of transcription) 6. This Jak-STAT pathway is central to the initiation of IL-4 activities. In this study, we identified the essential region for the proliferation signal and activation of Jak-1, Jak-3, and STAT6 in the cytoplasmic domain of the human IL-4 receptor alpha chain (hIL-4R alpha) using a mouse T cell line CTLL-2. We found that the region between amino acid 353 and 393 is critical for the proliferation signal and activation of STAT6, but not for tyrosine phosphorylation of Jaks. These results suggest that in addition to the "Box-1" portion, which is known to be essential for Jak-1 activation, the more membrane-distal region of hIL-4R alpha is also necessary for activation of STAT6.

Regulation of interleukin-13 receptor constituents on mature human B lymphocytes

Human B cells stimulated through both their immunoglobulin and CD40 receptors up-regulate 745 +/- 51 interleukin (IL)-13 ligand binding sites with an affinity of 0.91 +/- 0.08 nM within 24 h. IL-13 binds primarily to the IL-13Ralpha1 with subsequent sequestration of the IL-4Ralpha into the complex. IL-13Ralpha1 may also be found in those receptors capable of binding IL-4. gamma chain (gammac) participates in receptors capable of binding IL-4 but is not found in association with bound IL-13. Dimeric receptors composed of the IL-4Ralpha complexed with either the IL-13Ralpha1 or gammac occur simultaneously within defined B cell populations. mRNAs for all receptor constituents are increased subsequent to immunoglobulin stimulation alone, while maximal expression of IL-13Ralpha1 is more dependent upon co-stimulation of immunoglobulin and CD40 receptors. mRNA levels for IL-13Ralpha1 vary over a wider range subsequent to surface stimulation than other receptor components. Although gammac is not bound to IL-13 in B cells under the conditions evaluated, it may influence IL-13 binding by competing with IL-13Ralpha1 for association/sequestration with the IL-4Ralpha chain. IL-13Ralpha2 does not participate in the IL-13 receptor that is up-regulated upon activation of quiescent tonsillar B lymphocytes, although mRNA for the protein may be found in the centroblastic fraction of tonsillar cells.