Signal transduction pathway of interleukin-4 and interleukin-13 in human B cells derived from X-linked severe combined immunodeficiency patients

Interleukin-4 (IL-4) and IL-13 Enhance the Effect of IL-1β on Production of IL-1 Receptor Antagonist by Human Primary Hepatocytes and Hepatoma HepG2 Cells: Differential Effect on C-Reactive Protein Production

Interleukin-1 receptor antagonist (IL-1Ra) is produced by hepatocytes with characteristics of an acute-phase protein. To examine the role of IL-4 and IL-13 in production of IL-1Ra, human primary hepatocytes and HepG2 human hepatoma cells were cultured in the presence of IL-4 or IL-13 in combination with IL-1β and/or IL-6. The results indicated that both IL-4 and IL-13 amplified the stimulatory effect of IL-1β on production of IL-1Ra protein and messenger RNA (mRNA) by both human primary hepatocytes and HepG2 cells. IL-1Ra refers to three different peptides, one secreted (sIL-1Ra) and two intracellular (icIL-1RaI and icIL-1RaII), derived from the same gene. sIL-1Ra and icIL-1RaI are the products of two different mRNA, whereas icIL-1RaII is synthesized by alternative translation initiation mainly from sIL-1Ra mRNA. Our results show that both sIL-1Ra and icIL-1RaII, but not icIL-1RaI, are produced by HepG2 cells and human hepatocytes. Transient transfection experiments as well as mRNA stability studies indicated that IL-4 stimulated sIL-1Ra production primarly at the level of transcription. Gel retardation assays showed that IL-4 induced the formation of a STAT6-DNA complex with a STAT6 binding element within the sIL-1Ra promoter, but had no effect on IL-1–induced NF-κB binding activity. In contrast to IL-1Ra, production of C-reactive protein by human primary hepatocytes was stimulated by IL-6 and decreased by the addition of IL-4.

Cutting Edge: Dominant Effect of Ile50Val Variant of the Human IL-4 Receptor α-Chain in IgE Synthesis

Two variants of the IL-4R α-chain (IL-4Rα) gene have been recently identified in association with different atopic disorders. To clarify the etiological relationship between the two variants, we analyzed responsiveness to IL-4 of transfectants with four kinds of IL-4Rα carrying either Val or Ile at 50 and either Gln or Arg at 551. The substitution of Ile for Val augmented STAT6 activation, proliferation, and transcription activity of the Iε promoter by IL-4, whereas that of Arg for Gln did not change these IL-4 signals. Arg551 was not associated with atopic asthma in the Japanese population. CD23 expression and IgE synthesis by IL-4 were augmented in Ile50-bearing PBMC, compared with those bearing Val50. Taken together, substitution of Arg551 does not enhance the IL-4 signal for generation of germline ε transcript, whereas the substitution of Ile50 contributes to enhancement of IgE synthesis.

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.

Interleukin-4 and interleukin-13: their similarities and discrepancies

Interleukin-4 (IL-4) and the closely related cytokine, interleukin-13 (IL-13) share many biological and immunoregulatory functions on B lymphocytes, monocytes, dendritic cells and fibroblasts. Both IL-4 and IL-13 genes are located in the same vicinity on chromosome 5 and display identical major regulatory sequences in their respective promoters, thus explaining their restricted secretion pattern to activated T cells and mast cells. The IL-4 and IL-13 receptors are multimeric and share at least one common chain called IL-4R alpha. Recent progress made in the description of IL-4 and IL-13 receptor complex have demonstrated the existence of two types of IL-4 receptors: one constituted by the IL-4R alpha and the gamma c chain, and a second constituted by the IL-4 R alpha and the IL-13R alpha 1 and able to transduce both IL-4 and IL-13 signals. Specific IL-13 receptors are results from the association between the IL-4R alpha and the IL-13R alpha 2 or between two IL-13R alpha. Furthermore, similarities in IL-4 and IL-13 signal transduction have been also described, thus explaining the striking overlapping of IL-4- and IL-13-induced biological activities such as regulation of antibody production and inflammation. However, the restricted expression of IL-4 to type 2 helper T lymphocytes as well as the inability of IL-13 to regulate T cell differentiation due to a lack of IL-13 receptors on T lymphocytes represent the major differences between these cytokines. This would indicate that although IL-4 and IL-13 share a large number of properties, precise mechanisms of regulation are also present to guarantee their distinct functions.

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.

The distribution of IL-13 receptor alpha1 expression on B cells, T cells and monocytes and its regulation by IL-13 and IL-4

To study the expression of IL-13 receptor alpha1 (IL-13Ralpha1), specific monoclonal antibodies (mAb) were generated. Surface expression of the IL-13Ralpha1 on B cells, monocytes and T cells was assessed by flow cytometry using these specific mAb. Among tonsillar B cells, the expression was the highest on the IgD+ CD38- B cell subpopulation which is believed to represent naive B cells. Expression was also detectable on a large fraction of the IgD-CD38- B cells but not on CD38+ B cells. Activation under conditions which promote B cell Ig class switching up-regulated the expression of the receptor. However, the same stimuli had an opposite effect for IL-13Ralpha1 expression levels on monocytes. While IL-13Ralpha1 mRNA was clearly detectable in T cell preparations, no surface expression was detected. However, permeabilization of the T cells showed a clear intracellular expression of the receptor. A soluble form of the receptor was immunoprecipitated from the supernatant of activated peripheral T cells, suggesting that T cell IL-13Ralpha1 might have functions unrelated to the capacity to form a type II IL-4/IL-13R with IL-4Ralpha.

Role of JAK3 in CD40-Mediated Signaling

CD40 is a member of the tumor necrosis factor receptor family and plays an important role in B-cell survival, growth, differentiation, and isotype switching. Recently, CD40 has been shown to associate with JAK3, a member of the family of Janus Kinases, which are nonreceptor protein kinases involved in intracellular signaling mediated by cytokines and growth factors. To investigate the role of JAK3 in CD40-mediated signaling, we studied the effect of CD40 stimulation on B-cell proliferation, IgE isotype switching, and upregulation of surface expression of CD23, ICAM-1, CD80, and LT-α in JAK3-deficient patients. Our studies show that stimulation of B cells with monoclonal antibody to CD40 in the presence of interleukin-4 (IL-4) or IL-13 resulted in similar responses in JAK3-deficient patients and normal controls. This suggests that JAK3 is not essential for CD40-mediated B-cell proliferation, isotype switching, and upregulation of CD23, ICAM-1, CD80, and LT-α surface expression.

Role of JAK3 in CD40-Mediated Signaling

CD40 is a member of the tumor necrosis factor receptor family and plays an important role in B-cell survival, growth, differentiation, and isotype switching. Recently, CD40 has been shown to associate with JAK3, a member of the family of Janus Kinases, which are nonreceptor protein kinases involved in intracellular signaling mediated by cytokines and growth factors. To investigate the role of JAK3 in CD40-mediated signaling, we studied the effect of CD40 stimulation on B-cell proliferation, IgE isotype switching, and upregulation of surface expression of CD23, ICAM-1, CD80, and LT-α in JAK3-deficient patients. Our studies show that stimulation of B cells with monoclonal antibody to CD40 in the presence of interleukin-4 (IL-4) or IL-13 resulted in similar responses in JAK3-deficient patients and normal controls. This suggests that JAK3 is not essential for CD40-mediated B-cell proliferation, isotype switching, and upregulation of CD23, ICAM-1, CD80, and LT-α surface expression.

Human mast cells produce IL-13 by high-affinity IgE receptor cross-linking: enhanced IL-13 production by IL-4-primed human mast cells

BACKGROUND

Mast cells play a central role not only in the early phase of the allergic reaction, but also participate in the late phase of the allergic reaction through the allergen and IgE-dependent release of multifunctional cytokines.

OBJECTIVE

Using the recently established culture system for human mast cells, we examined the expression of a variety of cytokines in cord blood-derived human cultured mast cells (HCMCs) in response to different stimuli.

METHODS

HCMCs were grown from cord blood mononuclear cells in the presence of stem cell factor and IL-6 for 10 weeks. Cytokine mRNA expression in HCMCs by the different stimuli was examined by RT-PCR. Then taking 2 important cytokines, IL-13 and IL4, that share several functional properties and play important roles in allergic diseases, we examined protein as well as mRNA expression of both cytokines in HCMCs.

RESULTS

HCMCs did not express either IL-13 or IL-4 spontaneously. Stimulation with PMA + A23187 induced the expression of IL4 protein, as well as IL-13 protein, in their cytoplasm, although IL-4 secreted in the supernatant was below detectable levels in contrast to a significant amount of IL-13. Stimulation of HCMCs by cross-linking of the high-affinity IgE receptor (Fc(epsilon)RI) induced the expression of IL-13 mRNA and protein, but not IL4. Although we previously found that IL-4 upregulates Fc(epsilon)RI expression on HCMCs, when HCMCs were first cultured in the presence of IL4 and then activated through FC(epsilon)RI cross-linking, remarkable increase was found in IL-13 production. Furthermore, although IL-4 was still undetectable at protein level, IL-4 mRNA expression was induced in the IL-4-primed HCMCs stimulating Fc(epsilon)RI cross-linking. In addition, we examined the effects of these cytokines on the surface molecule expression in HCMCs. Although IL4 remarkably upregulated lymphocyte function-associated antigen-1, intercellular adhesion molecule-1, and Fc(epsilon)RI expression and downregulated c-kit expression in HCMCs, IL-13 did not.

CONCLUSIONS

Our observation that HCMCs produce IL-13 on cross-linking of Fc(epsilon)RI, which was enhanced by IL-4 priming, supports an important role of mast cells in amplification of allergic reaction and further suggests one of the mechanisms enhancing mast cell function in the microenvironment.

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.

Abrogation of bronchial eosinophilic inflammation and airway hyperreactivity in signal transducers and activators of transcription (STAT)6-deficient mice

Signal transducers and activators of transcription 6 (STAT6) is essential for interleukin 4-mediated responses, including class switching to IgE and induction of type 2 T helper cells. To investigate the role of STAT6 in allergic asthma in vivo, we developed a murine model of allergen-induced airway inflammation. Repeated exposure of actively immunized C57BL/6 mice to ovalbumin (OVA) aerosol increased the level of serum IgE, the number of eosinophils in bronchoalveolar lavage (BAL) fluid, and airway reactivity. Histological analysis revealed peribronchial inflammation with pulmonary eosinophilia in OVA-treated mice. In STAT6-deficient (STAT6-/-) C57BL/6 mice treated in the same fashion, there were no eosinophilia in BAL and significantly less peribronchial inflammation than in wild-type mice. Moreover STAT6-/- mice had much less airway reactivity than wild-type mice. These findings suggest that STAT6 plays a crucial role in the pathogenesis of allergen-induced airway inflammation.

Constitutive activation of Jak-2 and Tyk-2 in a v-Src-transformed human gallbladder adenocarcinoma cell line

It is well known that v-Src phosphorylates various substrates on tyrosine residue and associates with tyrosine-phosphorylated proteins as well as proline-rich ligands through its SH2 and SH3 domains, respectively, thereby inducing oncogenic transformation. A signal pathway from the cell surface to genes in the nucleus, the Jak/STAT (signal transducers and activators of transcription) pathway, has been shown to be involved in the signal transduction mechanism mediated by many cytokines and growth factors. Although a member of the STAT family, STAT3 has been reported to be constitutively activated in several v-Src-transformed cells, and it still remains unknown whether Jak molecules, which act upstream of STATs, are involved in the v-Src-induced activation mechanism of STAT3. In this study, we analyzed activations of both Jak and STAT molecules using v-Src-transformed HAG-1 cells derived from a human gallbladder adenocarcinoma. STAT3 was found to be constitutively activated in v-Src-transformed HAG-1 cells, but not in either non-transformed mock-transfected or activated c-H-ras-transfected HAG-1 cells, even though the other known STAT molecules are expressed. Furthermore, both Jak-2 and Tyk-2 were constitutively activated only in v-Src-transformed HAG-1 cells. Association of v-Src with either STAT3 or the Jak molecules was not observed. No change of this activation was detected by either interferon (IFN)-alpha2a or IFN-gamma, which had shown inhibitory effects on the growth of v-Src-transformed HAG-1 cells. These results raise the possibility that Jak-2 and Tyk-2 are both activated by v-Src, thereby contributing to the constitutive activation of STAT3 in the v-Src-transformed cells.

Activation of STAT5 by Lipopolysaccharide Through Granulocyte-Macrophage Colony-Stimulating Factor Production in Human Monocytes

LPS is a potent stimulator of monocytes, inducing many of their functions. Although the details of how LPS exerts such functions remain largely unknown, transcription factors such as nuclear factor-κB, nuclear factor-IL-6, and activator protein-1 have been shown to be involved in this process. However, to date it has been thought that no known STAT molecule plays a role in the activation of monocytes by LPS. In this study we examined whether some known STAT molecule is stimulated by LPS, based on the finding that a GAS motif sequence is conserved in the promoter regions of human, mouse, and rat cyclo-oxygenase-2 (COX-2) genes. Consequently, LPS induced activation of STAT5 in human monocytes, and this STAT5 activation occurred in an indirect way via granulocyte-macrophage CSF (GM-CSF) secreted by LPS-stimulated monocytes. Expression of COX-2 protein was partially reduced by treatment of anti-human GM-CSF Ab. Activation of STAT5 was inhibited by either IL-10 or dexamethasone (Dex), but not by aspirin. IL-10 blocked activation of STAT5 indirectly by suppressing GM-CSF production, while Dex inhibited this activation both directly and indirectly. Taken together, these results suggest that in addition to other transcription factors, STAT5 plays an important role in activation of monocytes by LPS, and that STAT5 is another target for IL-10 and Dex to inhibit COX-2 expression in activated monocytes.

A thiol antioxidant regulates IgE isotype switching by inhibiting activation of nuclear factor-kappaB

The binding site for nuclear factor-kappaB (NF-kappaB) is present at the promoter region of the germline Cepsilon gene, but there is little information on whether this factor is involved in regulating IgE synthesis by human B cells. Accordingly, we studied the role of NF-kappaB in germline Cepsilon transcription by using two human Burkitt's lymphoma B cell lines, DND39 and DG75. In both cell lines, n-acetyl-L-cysteine (NAC), a potent thiol antioxidant, inhibited the triggering of the nuclear expression of NF-kappaB by IL-4 and by anti-CD40 monoclonal antibody. Although IL-4 activated signal transducers and activators of transcription (STAT) 6 in addition to NF-kappaB, NAC treatment or the transfection of decoy oligodeoxynucleotides for NF-kappaB or STAT6 only partly blocked IL-4-induced germline Cepsilon transcription. However, these two decoy oligodeoxynucleotides together almost completely abrogated IL-4-induced germline Cepsilon transcription. Of note, CD40-mediated enhancement of IL-4-driven germline Cepsilon transcription was markedly decreased by NAC or by a decoy oligodeoxynucleotide for NF-kappaB. The effect of NAC was also examined on deletional switch recombination underlying the isotype switch to IgE. NAC inhibited the generation of Smu/Sepsilon switch fragments in normal human B cells costimulated with IL-4 and anti-CD40 monoclonal antibody. It also abolished IL-4-induced upregulation of CD40 but promoted upregulation of CD23. These results suggest that coordination of NF-kappaB and STAT6 may be required for induction of germline Cepsilon transcription by IL-4, and that CD40-mediated NF-kappaB activation may be important in regulating both enhancement of germline Cepsilon transcription and class switching to IgE.

Structural and Functional Basis for JAK3-Deficient Severe Combined Immunodeficiency

Mutations of the Janus family kinase JAK3 have been found to be responsible for autosomal recessive severe combined immunodeficiency (SCID) in humans. We report here the analysis of four new unrelated patients affected by JAK3-deficient SCID. The genetic defects were heterogeneous and included a large intragenic deletion as well as different point mutations, leading to missense substitutions, early stop codons, or splicing defects. We performed a series of studies of the biochemical events induced by cytokines on lymphoblastoid B-cell lines obtained from these patients. Abnormalities in tyrosine phosphorylation of JAK3 in response to interleukin-2 (IL-2) and IL-4 were present in all patients. Accordingly, IL-2–mediated phosphorylation of STAT5 was also absent or barely detectable. On the contrary, in all cases, we could show reduced but clear phosphorylation of STAT6 upon IL-4 stimulation. In one patient carrying a single amino acid change (Glu481Gly) in the JH3 domain of JAK3, we observed partially conserved IL-2 responses resulting in reduced but detectable levels of JAK3 and STAT5 phosphorylation. Interestingly, the patient bearing this mutation developed a substantial number of circulating CD4+/CD45RO+ activated T lymphocytes that were functionally impaired. In two cases, patients' cells expressed JAK3 proteins with mutations in the JH2 pseudo-kinase domain. A single cysteine to arginine substitution (Cys759Arg) in this region resulted in high basal levels of constitutive JAK3 tyrosine phosphorylation unresponsive to either downregulation by serum starvation or cytokine-mediated upregulation. The characterization of the genetic defects and biochemical abnormalities in these JAK3-deficient patients will help define the role of JAK3 in the ontogeny of a competent immune system and may lead to a better understanding of the JAK3 functional domains.

Modulation of interleukin (IL)-13 binding and signaling by the gammac chain of the IL-2 receptor

Interleukin (IL)-13 and IL-4 are cytokine products of TH2 cells which exert similar effects in a variety of cell types. We recently described IL-13R expression on human renal cell and colon carcinoma cells and demonstrated that gammac is not a component of IL-13R or IL-4R systems in these cells. In lymphoid cells such as B cells and monocytes, which respond to IL-13, gammac is a component of IL-4R but does not appear to be a component of IL-13R. Furthermore, while significant IL-13 binding is observed on carcinoma cells, IL-13 barely binds these lymphoid cells and the binding characteristics are different. To better understand the role of gammac in IL-13 binding and signaling, we have transfected a renal cell carcinoma cell line with gammac and examined IL-13 and IL-4 binding and signaling. IL-13 binding as well as IL-13 and IL-4 signaling through the JAK-STAT signaling pathway were severely inhibited. This inhibition was paralleled by a loss of expression of one of the IL-13R chains and intercellular cell adhesion molecule-1. Thus, although gammac has been shown to enhance IL-4 binding and function in some cell types, its influence on IL-13R function in tumor cells appear to be largely negative.

Homodimerization of the human interleukin 4 receptor alpha chain induces Cepsilon germline transcripts in B cells in the absence of the interleukin 2 receptor gamma chain

The cytokines interleukin (IL)-4 and IL-13 play a critical role in inducing Cepsilon germline transcripts and IgE isotype switching in human B cells. The IL-4 receptor (IL-4R) in B cells is composed of two chains, the IL-4-binding IL-4Ralpha chain, which is shared with the IL-13R, and the IL-2Rgamma (gammac) chain, which is shared with IL-7R, IL-9R, and IL-15R. IL-4 induces Cepsilon germline transcripts and IgE isotype switching in B cells from patients with gammac chain deficiency. Induction of Cepsilon germline transcripts by IL-4 in B cells that lack the gammac chain may involve signaling via the IL-13R. Alternatively, the IL-4Ralpha chain may transduce intracellular signals that lead to Cepsilon gene transcription independently of its association with other chains. We show that ligand-induced homodimerization of chimeric surface receptors consisting of the extracellular and transmembrane domains of the erythropoietin receptor and of the intracellular domain of IL-4Ralpha induces Janus kinase 1 (Jak1) activation, STAT6 activation, and Cepsilon germline transcripts in human B cell line BJAB. Disruption of the Jak1-binding proline-rich Box1 region of IL-4Ralpha abolished signaling by this chimeric receptor. Furthermore, B cells transfected with a chimeric CD8alpha/IL-4Ralpha receptor, which is expressed on the cell surface as a homodimer, constitutively expressed Cepsilon germline transcripts. These results suggest that homodimerization of the IL-4Ralpha chain is sufficient to transduce Jak1-dependent intracellular signals that lead to IgE isotype switching.

Chromosome mapping and expression of the human interleukin-13 receptor

Interleukin-13 (IL-13) is a cytokine secreted by activated T cells and shares most but not all biological activities with interleukin-4 (IL-4). Both cytokines play an important role as a switch factor directing synthesis of IgE; they act on monocytes and endothelial cells, but unlike IL-4, IL-13 does not act on T cells. These cytokines have both common and distinct components in their respective receptors. Based on sequence similarity shared by cytokine receptor family members, we have identified a cDNA encoding the human IL-13 receptor (IL-13R). This cDNA was used to examine the pattern of IL-13R mRNA expression by Northern blot analyses of poly(A)+ RNA purified from different human tissues and cell lines. Among several myeloma cell lines analyzed, the U266 cell line was the only one found to express IL-13R transcripts. This cell line is also the only one described as producing IgE. The IL-13R gene was mapped to chromosome Xq24 by in situ hybridization. Interestingly, this locus is near that of the CD40 ligand gene, the product of which is also involved, like IL-13, in proliferation and IgE isotype switching of human B cells. The human IL-13R gene maps between two cytokine receptor genes located on the chromosome arm Xq region: the interleukin-2 receptor gamma chain gene (Xq13.1) and the interleukin-9 receptor gene (Xq28). The lack of nucleotide sequence similarity suggests unrelated evolutionary pathways between these receptor genes.

A novel 4-kb interleukin-13 receptor alpha mRNA expressed in human B, T, and endothelial cells encoding an alternate type-II interleukin-4/interleukin-13 receptor

A 4 kb human interleukin-13 receptor (IL-13R) chain cDNA was cloned from a B cell cDNA library using expressed sequence tags homologous to mouse IL-13R as probes. The deduced protein sequence shows a significant level of sequence identity with the IL-5R and the human IL-13R identified recently by expression cloning. The cytoplasmic region is very highly conserved between human and mouse homologs and contains a consensus binding motif for a signal transducer and activator of transcription. The cDNA encodes a protein binding IL-13 when expressed alone which participates in a receptor complex for both IL-4 and IL-13 when expressed in conjunction with the IL-4R alpha chain. Transcripts for this IL-13R chain could be detected in most tissues and organs studied and in T, B, endothelial cells, basophilic, immature mast cell, and monocytic cell lines. The pattern of expression is different from the other recently cloned IL-13R molecule, and correlates with sites where IL-4 and IL-13 signaling is known to occur. This novel receptor is therefore likely to be implicated in reactions involved in IgE responses, T helper 2 differentiation, adhesion of leukocytes to endothelium, and therefore in pathological phenomena such as allergy, atopy, and asthma.

Interleukin-4 signaling in B lymphocytes from patients with X-linked severe combined immunodeficiency

Interleukin-4 (IL-4) is an important cytokine for B and T lymphocyte function and mediates its effects via a receptor that contains gammac. B cells derived from patients with X-linked severe combined immunodeficiency (X-SCID) are deficient in gammac and provide a useful model in which to dissect the role of this subunit in IL-4-mediated signaling. We found that although IL-4 stimulation of X-SCID B cells did not result in Janus tyrosine kinase-3 (JAK3) phosphorylation, other IL-4 substrates including JAK1 and IRS-1 were phosphorylated. Additionally, we detected signal transducers and activators of transcription 6 (STAT6) tyrosine phosphorylation and DNA binding activity in X-SCID B cells with a wide range of gammac mutations. However, reconstitution of these X-SCID B cells with gammac enhanced IL-4-mediated responses including STAT6 phosphorylation and DNA binding activity and resulted in increased CD23 expression. Thus, gammac is not necessary to trigger IL-4-mediated responses in B cells, but its presence is important for optimal IL-4-signaling. These results suggest that two distinct IL-4 signaling pathways exist.

Shared gamma(c) subunit within the human interleukin-7 receptor complex. A molecular basis for the pathogenesis of X-linked severe combined immunodeficiency

Genetic evidence suggests that mutations in the gamma(c) receptor subunit cause X-linked severe combined immunodeficiency (X-SCID). The gamma(c) subunit can be employed in receptor complexes for IL-2, -4, -7, -9, and -15, and the multiple signaling defects that would result from a defective gamma(c) chain in these receptors are proposed to cause the severe phenotype of X-SCID patients. Interestingly, gene disruption of either IL-7 or the IL-7 receptor (IL-7R) alpha subunit in mice leads to immunological defects that are similar to human X-SCID. These observations suggest the functional importance of gamma(c) in the IL-7R complex. In the present study, structure/function analyses of the IL-7R complex using a chimeric receptor system demonstrated that gamma(c) is indeed critical for IL-7R function. Nonetheless, only a limited portion of the cytoplasmic domain of gamma(c) is necessary for IL-7R signal transduction. Furthermore, replacement of the gamma(c) cytoplasmic domain by a severely truncated erythropoeitin receptor does not affect measured IL-7R signaling events. These findings support a model in which gamma(c) serves primarily to activate signal transduction by the IL-7R complex, while IL-7R alpha determines specific signaling events through its association with cytoplasmic signaling molecules. Finally, these studies are consistent with the hypothesis that the molecular pathogenesis of X-SCID is due primarily to gamma(c)-mediated defects in the IL-7/IL-7R system.

Naturally occurring primary deficiencies of the immune system

Naturally occurring genetic disorders of the immune system provide many models for the study of its development and function. In a way, their analysis complements the information provided by the generation of genetic defects in mice created using homologous recombination techniques. In this review, the recent findings made in three areas are focused upon deficiencies in T cell differentiation and in T lymphocyte activation, and on the control process of peripheral immune response.

Interleukin-13 is a potent activator of JAK3 and STAT6 in cells expressing interleukin-2 receptor-gamma and interleukin-4 receptor-alpha

The lymphocyte growth factors interleukin-2 (IL2), IL4, IL7, IL9 and IL15 use the common IL2 receptor-gamma (IL2R gamma) and activate the IL2R gamma-associated tyrosine kinase JAK3 (Janus kinase 3). IL13 is structurally related to IL4, competes with IL4 for binding to cell surface receptors and exhibits many similar biological effects. The molecular basis for this functional overlap between IL4 and IL13 has been attributed mainly to a shared use of the 140 kDa IL4R alpha, since these cytokines appear to be uniquely different in that, according to several recent reports, IL13 does not recruit the IL2R gamma or JAK3. This notion has been supported by the identification of a novel 70 kDa IL13 receptor in certain IL13-responsive cell lines that lack IL2R gamma. The present study sheds new light on the issue of functional overlap between IL13 and IL4, by demonstrating for the first time that, in cells that express both IL2R gamma and IL4R alpha, IL13 can mimic IL4-induced heterodimerization of IL2R gamma and IL4R alpha, with consequent marked activation of JAK3 and the transcription factor STAT6 (IL4-STAT). Reconstitution experiments in BA/F3 cells showed that both cytokines require the simultaneous presence of IL4R alpha and IL2R gamma to mediate JAK3 and proliferative responses, and analysis of 12 IL4R alpha variants showed that IL4 and IL13 signals were equally affected by mutations of the cytoplasmic domain. We conclude that IL13 activates the IL2R gamma-associated JAK3 tyrosine kinase in appropriate cell types, and propose that IL13 is capable of interacting with multiple receptor subunits in a cell-dependent and combinatorial manner. Consequently, we predict that partial disruption of IL13 signal transduction also contributes to the severe combined immuno-deficiency syndromes associated with inactivation of the IL2R gamma or JAK3 genes.

Requirements for interleukin-4-induced gene expression and functional characterization of Stat6

Interleukin-4 (IL-4) stimulation leads to the activation of the signal transducer and activator of transcription 6 (Stat6). In this study, we present data relating to the functional properties of Stat6. Human embryonic kidney 293 cells were shown to be deficient of Stat6 yet express all other components of the IL-4 signaling cascade. This cell line was used for transient-transfection studies of wild-type and mutant Stat6 proteins. The wild-type protein was shown to activate a reporter construct carrying multiple copies of the IL-4 response element derived from the human immunoglobulin heavy-chain germ line epsilon promoter. Similarly, a truncated protein lacking 41 amino acids of the N terminus was fully active. However, removal of the C-terminal 186 amino acids completely abolished transcription activation. Amino acid substitutions were introduced into the putative DNA binding domain (VVI at positions 411 to 413), the SH2 domain (R-562), or the tyrosine (Y-641) which presumably becomes phosphorylated upon activation. All three of these Stat6 mutants were unable to activate transcription in 293 cells. Wild-type and mutant Stat6 derivatives were also expressed in insect cells, and purified proteins were analyzed in vitro for the ability to interact with both DNA and tyrosine-phosphorylated peptides derived from the IL-4 receptor alpha chain. Mutations within the DNA binding domain, the SH2 domain, or tyrosine 641 completely abolished DNA binding. In contrast, only the SH2 mutant failed to interact with tyrosine-phosphorylated peptides. The transdominant effects of all Stat6 derivatives were analyzed by using HepG2 cells, which express endogenous Stat6 protein. Differential effects were observed with various mutants, supporting the current model of the Jak/STAT activation cycle.

IL4 and IL13 receptors share the gamma c chain and activate STAT6, STAT3 and STAT5 proteins in normal human B cells

IL13 induces the same biological effects as IL4 in normal human B cells. We show that as in the IL4R complex, both IL4R alpha and IL2R gamma c are components of the IL13R and that both cytokines induced STAT6, STAT3 and STAT5 activation in B cells. In spite of this similar downstream signalling, IL4 and IL13 used a different set of Janus kinases: IL13 is unable to activate JAK1 and JAK3.