Cloning of the mouse interleukin 2 receptor gamma chain: demonstration of functional differences between the mouse and human receptors

Human and murine IL2 receptors differentially respond to the human-IL2 component of immunocytokines

The humanized immunocytokine, hu14.18-IL2 (ICp), leads to the immune cell-mediated destruction of GD2-expressing tumors in mouse models, resulting in potent antitumor effects with negligible IL2-related toxicity. In contrast, when ICp is used clinically, antitumor activity is accompanied by dose-limiting IL2-related toxicities. These species-specific differences in ICp toxicity may be linked to differential binding to mouse vs. human IL2 receptors (IL2Rs). We evaluated immunocytokines genetically engineered to preferentially bind either high-affinity αβγ-IL2Rs or intermediate-affinity βγ-IL2Rs. These ICs have the IL2 fused to the C-terminus of the IgG light chains rather than the heavy chains. We found that IC35, containing intact huIL2, maintained activation of human and mouse αβγ-IL2Rs but exhibited a 20-fold reduction in the ability to stimulate human βγ-IL2Rs, with no activation of mouse βγ-IL2Rs at the concentrations tested. The reduced ability of IC35 to stimulate human βγ-IL2Rs (associated with IL2-toxicities) makes it a potential candidate for clinical trials where higher clinical IC doses might enable better tumor targeting and increased antitumor effects with less toxicity. Contrastingly, ICSK (IC with an IL2 mutein that has enhanced binding to the IL2R β-chain) showed increased activation over ICp on mouse βγ-IL2Rs, with a dose-response curve similar to that seen with IC35 on human βγ-IL2Rs. Our data suggest that ICSK might be used in mouse models to simulate the anticipated effects of IC35 in clinical testing. Understanding the differences in species-dependent IL2R activation should facilitate the design of reagents and mouse models that better simulate the potential activity of IL2-based immunotherapy in patients.

Different strategies for producing naturally soluble form of common cytokine receptor γ chain

The common cytokine receptor γ chain (γc) plays an essential role in regulating lymphoid homeostasis. In fact, alteration of this gene causes severe immunodeficiency in humans and animals. Although soluble γc (sγc) was identified in the late 1990s, much remains unknown about its production. This study describes various mechanisms underlying the generation of sγc isoforms in different species. Our data demonstrate that mouse γc and the avian ortholog γc-a did not generate sγc. Moreover, two mouse isoforms, CRA-a and mγc-b, encoded by transcripts lacking a transmembrane region by alternative splicing, did not yield sγc. However, in ducks, sγc was produced from a γc-b transcript lacking a transmembrane region by alternative splicing. In chickens, sγc was produced in normal cells and cell lines by proteolytic shedding of the γc-b isoform containing intron 5, which displayed a relatively high probability of proteolytic cleavage of the ectodomain. This shedding was suppressed by leupeptin, serine and cysteine protease inhibitor. Compared to the chicken ortholog γc-a, expression of γc-b mRNA was differentially regulated according to tissue type, developmental stage, and antigen stimulation. These data demonstrate several mechanisms for producing sγc and suggest a potential role for sγc in avian lymphoid homeostatic responses to environmental antigens.

A mutation in the IL-2 receptor gamma chain gene associated with X-linked severe combined immunodeficiency accompanying opisthotonus

Severe combined immunodeficiency (SCID) is an inherited disease with profoundly defective T cells, B cells, and NK cells. X-linked severe combined immunodeficiency (X-SCID) is its most common form. In this report, we describe a 4-month old male with X-SCID who also showed opisthotonic posturing. Opisthotonus represents abnormal motor posturing and is defined as the posturing, in which the neck and back are arched posteriorly. The patient was referred to our hospital with liver dysfunction, respiratory distress, anal abscess, poor feeding and wasting; the patient appeared to suffer from severe and persistent infections. In fact, circulating T cells were not detectable, despite that the number of B cells was maintained in the normal ranges. Diagnosis of X-SCID was established by DNA analysis of the interleukin (IL)-2 receptor gamma chain gene; namely, we detected the novel mutation within exon 2 (221 C-->A), which leads to the substitution of tyrosine codon for stop codon (Y69stop). Computed tomography of the brain revealed mild atrophy, but no hemorrhage and no malformation. There were no pathological findings in the cerebrospinal fluid. Thus, the cause of opisthotonic posturing remains unknown. The patient died due to severe infection at the age of 7 months. It remains to be investigated to clarify the relationship between the mutation and clinical manifestations. In conclusion, we have identified the novel mutation in the IL-2 receptor gamma chain gene, which is associated with X-SCID. Furthermore, this is the first report that describes the patient with X-SCID accompanying opisthotonus.

Interleukin 15 and its receptor

Interleukin 15 (IL-15) is a member of the four-helix bundle cytokine family that shares many in vitro biological activities with IL-2. Previous work demonstrated that IL-15 utilizes the beta and gamma chains of the IL-2 receptor (IL-2R), and that these are essential for IL-15-mediated signal transduction. However, several lines of evidence indicated the existence of an additional, IL-15-specific receptor component. An IL-15 binding chain was identified on a murine T cell clone, and direct expression cloning was used to isolate the corresponding cDNA. The predicted structure of this protein shows sequence similarity to the IL-2R alpha chain. Transfection of this cDNA into a murine, IL-3-dependent myeloid cell line, 32D-01, conferred IL-15 binding and, together with transfection of the IL-2R beta chain, rendered the cells responsive to IL-15 stimulation. This experiment confirmed that the IL-15 binding chain is part of the IL-15 receptor, and it is designated as the IL-15R alpha subunit. The expression pattern of the IL-15R alpha mRNA is distinct from that of IL-2R alpha mRNA. Recombinant expression of a soluble form of IL-15R alpha demonstrated that it is a potent inhibitor of IL-15 biological activity.

IL-2 responsiveness of CD4 and CD8 lymphocytes: further investigations with human IL-2Rbeta transgenic mice

Responsiveness to IL-2 varies from one lympho-mononuclear subset to another. NK lymphocytes and monocytes spontaneously respond to IL-2 whereas it is generally accepted that T and B lymphocytes need to be activated to fully acquire this competence. To further investigate this phenomenon, we studied human IL-2Rbeta (hIL-2Rbeta) transgenic mice constitutively expressing heterospecific, intermediate-affinity IL-2R (hIL-2Rbeta/mouse IL-2Rgamma(c)). We noted that the B lymphocytes and monocytes from spleens of these hIL-2Rbeta transgenic animals failed to grow when cultured in IL-2-containing medium. Under the same experimental conditions, CD4 lymphocytes survived, again without growth, whereas CD8 lymphocytes and NK cells were able to proliferate and develop potent LAK cytotoxicity. The properties of these CD4 and CD8 lymphocytes were then compared after purification. Both subsets expressed functional IL-2R able to induce global protein phosphorylation and, more precisely, signal transducer and activation of transcription 5 and Erk phosphorylation. Therefore, the differential growth potential of these CD4 and CD8 lymphocytes cannot be explained by the lack of IL-2R-dependent early signaling events. When the entrance of purified CD4 and CD8 lymphocytes into the cell cycle was analyzed, we found that the CD4 lymphocytes were unable to enter the G1 phase in the absence of anti-CD3 stimulation. This correlates with the effect of IL-2 on cyclin-dependent kinase inhibitor p27(kip1). In CD4 lymphocytes, IL-2 does not affect p27(kip1) expression. But in CD8 lymphocytes, IL-2 down-modulates p27(kip1). These results indicate that, aside from IL-2R expression and function, IL-2 responsiveness is also controlled by lineage-specific mechanisms.

Soluble thymic stromal lymphopoietin receptors are absent in murine sera--detection with anti-mTSLPR monoclonal antibodies

Two monoclonal antibodies, termed nnIE11 and nnIG11, were generated against the murine thymic stromal lymphopoietin receptor, mTSLPR, using traditional hybridoma technology. The antibody-producing hybridoma clones were obtained by fusing P3X63-Ag8.653 myeloma cells with splenocytes from Balb/c mice immunized with anti-FLAG M2 affinity-purified FLAG-tagged mTSLPR from pSVL-mTSLPR-FLAG-transfected COS cells and Ni-NTA-purified his-tagged mTSLPR from recombinant FastBacHisB-mdelta1 baculovirus-infected Sf9 cells. Several monoclonal anti-mTSLPR-specific hybridoma clones were obtained and two of these clones are further characterized here. The generated antibodies could in an immunoblotting identify baculovirus-expressed mTSLPR proteins with a molecular weight corresponding to 50 kDa. Both immunoblotting and ELISA with recombinant mouse TSLPR/Fc chimera as antigen, having only the N-terminal domain of mTSLPR present, indicated that the generated monoclonal antibodies identify the C-terminus of mTSLPR. Although sandwich ELISAs performed with a goat anti-mTSLPR antiserum as capture antibody and nnIE11 as indicator antibody were able to detect mTSLPR in the range of 5 ng/ml, no souble mTSLPR could be observed in serum samples from CBA/H, Balb/c and C57Bl/6 mice.

A neurogenomics approach to gene expression analysis in the developing brain

Secreted and transmembrane proteins provide critical functions in the signaling networks essential for neurogenesis. We used a genetic signal sequence gene trap approach to isolate 189 genes expressed during development in e16.5 whole head, e16.5 hippocampus and e14.5 cerebellum. Gene ontology programs were used to classify the genes into respective biological processes. Four major classes of biological processes known to be important during development were identified: cell communication, cell physiology processes, metabolism and morphogenesis. We used in situ hybridization to determine the temporal and spatial patterns of gene expression in the developing brain using this set of probes. The results demonstrate that gene expression patterns can highlight potential gene functions in specific brain regions. We propose that combining bioinformatics with the gene expression pattern is an effective strategy to identify genes that may play critical roles during brain development.

X-linked severe combined immunodeficiency syndrome: the first Korean case with gamma c chain gene mutation and subsequent genetic counseling

X-linked severe combined immunodeficiency (X-SCID) is a rare, life-threatening immune disorder, caused by mutations in the gamma c chain gene, which encodes an essential component of the cytokine receptors for interleukin-2 (IL-2), IL-4, IL-7, IL-9, IL-15, and IL-21. A 13-month-old boy with recurrent infections who had reduced serum immunoglobulin levels and decreased numbers of CD3, CD16/56 cells was evaluated for gamma c chain gene mutation and protein expression. The patient had a C-to-T point mutation at nucleotide position 690, one of the hot spots, resulting in a single amino acid substitution of cysteine for arginine (R226C), as determined by direct sequencing and PCR-RFLP. The patient's mother was a heterozygous carrier. Percutaneous umbilical cord blood sampling was performed at the 6-month of gestation in a subsequent pregnancy. As the immunophenotype of the fetus showed an identical pattern, the pregnancy was terminated and genetic analysis of the abortus confirmed recurrence. This is the first report of the molecular diagnosis of X-SCID in Korea. Genetic analysis of the gamma c chain gene is useful for definite diagnosis and genetic counseling for X-SCID.

Identification of an alternatively spliced isoform of the common cytokine receptor gamma chain in chickens

The common cytokine receptor gamma(gamma(c)) chain is shared by at least six cytokine receptors and plays a critical role in the regulation of immune responses. In this study, we discovered that, unlike mammals, chickens possess two different gamma(c) gene transcripts, chgamma(c)-a and chgamma(c)-b. Sequence comparisons between the cDNAs and a gamma(c) genomic clone isolated by PCR revealed that chgamma(c)-b contained an in-frame 78bp insertion between Gly-222 and Val-223 of the chgamma(c)-a sequence. This insertion most likely resulted from alternative splicing such that the fifth intron was not removed from the chgamma(c)-b transcript. Furthermore, while chgamma(c)-a and chgamma(c)-b transcripts were expressed equally in the spleen, thymus, bursa, and cecal tonsils, they were differentially expressed during the time course of Con A stimulation of splenic T lymphocytes. Western blot analysis of normal spleen lymphocytes identified 45, 53, and 64 kDa immunoreactive bands whereas only 64kDa band was detected in Con A-activated splenic lymphocytes. COS-7 cells transfected with chgamma(c)-b secreted approximately 42kDa proteins. Taken together, our results document that chickens express an alternative spliced gamma(c) receptor which is larger than the conventional transcript and this novel isoform generates soluble receptors in the transfected COS-7 cells.

Interleukin-15 interactions with interleukin-15 receptor complexes: characterization and species specificity

Interleukin (IL-) 2 and IL-15 share the IL-2 receptor betagamma c subunits (IL-2Rbetagamma c) but have specific, unique alpha receptor subunits. We studied species specificity of human (hu), simian (si), and mouse (mu) IL-15 and found that hu and si IL-15 behaved similarly in all systems investigated. Hu and mu IL-15 bound hu or mu IL-15Ralpha with equal high affinity in the presence or absence of IL-2Rbetagamma c and exhibited similar proliferative activities on cells containing all three subunits. However, quantitative differences were noted in the specific activity of hu and mu IL-15 in both in vitro and in vivo systems utilizing IL-2Rbetagamma c in the absence of IL-15Ralpha. These data show that hu IL-15 may be used in mouse model systems, however care must be taken when comparing the efficacy and toxicity of cytokines across species.

No soluble common cytokine receptor gamma chain (gamma(c)) in activated human lymphocyte cultures-comparison with soluble IL-2Ralpha

The presence of a soluble form of the common cytokine receptor gamma chain (gamma(c)) in cell free supernatants from unstimulated and 1-6 days PHA stimulated peripheral blood lymphocyte (PBL) cultures was analyzed using a sandwich ELISA. No naturally produced soluble gamma(c) could be detected in these cell free culture supernatants, although a sensitivity in the nanogram range was achieved for recombinant baculovirus expressed human soluble gamma(c) with this assay (detection limit 0.2 ng hIL-2 sRgamma). Analysis of the very same supernatants for soluble IL-2Ralpha demonstrated increased concentrations (up to 20.4 ng/ml) of this other IL-2R member. The membrane-associated form of the common cytokine receptor gamma chain was detected in cell lysates prepared from stimulated PBL at a concentration of 3.5 ng per 0.5 x 10(6) cells. Analysis of a small panel of serum samples from patients with different disorders verified that the soluble form of hIL-2Ralpha, but not hIL-2 sRgamma, can be detected, which thereby strongly suggests that the human soluble gamma(c) seems to be a valuable marker only for a limited number of clinical disorders.

Functional epitope of common gamma chain for interleukin-4 binding

Interleukin 4 (IL-4) can act on target cells through an IL-4 receptor complex consisting of the IL-4 receptor alpha chain and the common gamma chain (gamma(c)). An IL-4 epitope for gamma(c) binding has previously been identified. In this study, the gamma(c) residues involved in IL-4 binding were defined by alanine-scanning mutational analysis. The epitope comprises gamma(c) residues I100, L102, and Y103 on loop EF1 together with L208 on loop FG2 as the major binding determinants. These predominantly hydrophobic determinants interact with the hydrophobic IL-4 epitope composed of residues I11, N15, and Y124. Double-mutant cycle analysis revealed co-operative interaction between gamma(c) and IL-4 side chains. Several gamma(c) residues involved in IL-4 binding have been previously shown to be mutated in X-linked severe combined immunodeficiency. The importance of these binding residues for gamma(c) function is discussed. These results provide a basis for elucidating the molecular recognition mechanism in the IL-4 receptor system and a paradigm for other gamma(c)-dependent cytokine receptor systems.

Interdependence of cdk2 activation and interleukin-2Ralpha accumulation in T cells

We have shown previously that serum promotes T cell proliferation by acting with T cell receptor (TCR) agonists to efficiently down-regulate p27(Kip1) and activate cdk2-containing complexes. In the studies described here, the effect of serum on the expression of the alpha subunit of the interleukin-2 receptor (IL-2Ralpha) was examined. We found that serum was required for maximal and sustained IL-2Ralpha protein expression and consequent IL-2 signaling in TCR-activated splenocytes. Serum had no effect on IL-2Ralpha mRNA levels and thus modulates IL-2Ralpha expression post-transcriptionally. Unlike wild-type splenocytes, splenocytes exhibiting serum-independent cdk2 activation due to loss of p27(Kip1) efficiently expressed IL-2Ralpha in serum-deficient medium. Conversely, serum did not promote IL-2Ralpha accumulation in conditions in which cdk2 activity was blocked. These findings demonstrate that cdk2 activation is necessary and sufficient for IL-2Ralpha accumulation in TCR-stimulated splenocytes. On the other hand, IL-2 signaling was required (at least in part) for cdk2 activation in these cells. Thus, cdk2 activation, IL-2Ralpha expression, and IL-2 signaling are interdependent events, and we suggest that this feed-forward regulatory loop plays a key role in T cell mitogenesis.

Cloning of a receptor subunit required for signaling by thymic stromal lymphopoietin

Signaling by type I cytokines involves the formation of receptor homodimers, heterodimers or higher order receptor oligomers. Here we report the cloning of a type I cytokine receptor subunit that is most closely related to the common cytokine receptor gamma chain (gamma c). Binding and crosslinking experiments demonstrate that this protein is the receptor for a recently described interleukin 7 (IL-7)-like factor, thymic stromal lymphopoietin (TSLP). Binding of TSLP to the thymic stromal lymphopoietin receptor (TSLPR) is increased markedly in the presence of the IL-7 receptor alpha chain (IL-7R alpha). IL-7R alpha-expressing but not parental 32D cells proliferate in the presence of exogenous TSLP. Moreover, a combination of IL-7R alpha and TSLPR is required for TSLP-dependent activation of a STAT5-dependent reporter construct. Thus it is shown that IL-7R alpha is a component of both the IL-7 and TSLP receptors, which helps to explain why deletion of the gene that encodes IL-7R alpha affects the lymphoid system more severely than deletion of the gene encoding IL-7 does. Cloning of TSLPR should facilitate an understanding of TSLP function and its signaling mechanism.

Regulation of T cell cytokine production by dendritic cells

Previous work has established that the dendritic cells (DC) of mouse spleen regulate the IL-2 production, and hence the extent of proliferation, of the CD8 T cells they activate. It is now reported here that interaction of primary CD8 T cells with splenic CD8alpha- DC induced much higher production of IL-3, IFN-gamma and granulocyte-macrophage colony-stimulating factor (GM-CSF), as well as IL-2, than did interaction with CD8alpha+ splenic DC. Furthermore, the CD8alpha- DC also induced higher levels of IL-2, IL-3 and IL-10 production in primary CD4 T cells, compared with that induced by CD8alpha+ DC. These quantitative differences did not involve qualitative shifts in the type of cytokine produced. Interleukin-4 production remained low in all the primary T cell cultures and restimulation experiments in secondary cultures did not reveal any bias in the cytokine production profile. When exogenous IL-2 was added to the primary cultures to ensure equal proliferation in response to CD8alpha- or CD8alpha+ DC, the higher level of production of IL-3, IFN-gamma and GM-CSF induced by CD8alpha- DC was maintained. Thus, this general control of T cell cytokine production by splenic DC involves factors additional to those that govern activation of T cells into cell cycle.

Lymphoid development and function in X-linked severe combined immunodeficiency mice after stem cell gene therapy

Mutations of the common gamma chain (gammac) of cytokine receptors cause X-linked severe combined immunodeficiency (XSCID), a candidate disease for gene therapy. Using an XSCID murine model, we have tested the feasibility of stem cell gene correction. XSCID bone marrow (BM) cells were transduced with a retroviral vector expressing the murine gammac (mgammac) and engrafted in irradiated XSCID animals. Transplanted mice developed mature B cells, naive T cells, and mature natural killer (NK) cells, all of which were virtually absent in untreated mice. The mgammac transgene was detected in all treated mice, and we could demonstrate mgammac expression in newly developed lymphocytes at both the RNA and protein level. In addition, treated mice showed T cell proliferation responses to mitogens and production of antigen-specific antibodies upon immunization. Four of seven treated animals showed a clear increase of the transgene positive cells, suggesting in vivo selective advantage for gene-corrected cells. Altogether, these results show that retroviral-mediated gene transfer can improve murine XSCID and suggest that similar strategies may prove beneficial in human clinical trials.

Interleukin-4 and interleukin-10 regulate IL1-beta induced mouse primary astrocyte activation: a comparative study

The pro-inflammatory cytokine interleukin-1beta (IL-1beta) is strongly expressed during brain injury and is able to induce severe cellular brain damage via the production of soluble factors. Different processes regulate IL-1 biological activities, like the production of anti-inflammatory cytokines such as interleukin-4 (IL-4) and interleukin-10 (IL-10). In this report, we describe the sequential effects of IL-4 and IL-10 on the production of interleukin-6 (IL-6) induced by IL-1beta in mouse primary astrocytes and compare these effects to those of the synthetic glucocorticoid agonist, dexamethasone. IL-6 secretion and IL-6 mRNA expression were determined by ELISA assay and a comparative RT-PCR method, respectively. Incubation of mouse astrocytes in primary culture simultaneously with IL-1beta (10 ng/ml) + IL-10 (10 ng/ml) or IL-1beta + dexamethasone (10(-6) M) markedly reduced IL-1beta induced IL-6 secretion and IL-6 mRNA expression, respectively, whereas simultaneous addition of IL-4 (10 ng/ml) did not alter the induction of IL-6 by IL-1beta. In contrast, after 24 h of IL-1beta treatment, the level of IL-6 was decreased below constitutive levels, and this change was reversed by addition of IL-4. IL-6 production in IL-1beta pretreated cells was also increased by addition of IL-4, whereas IL-10 and dexamethasone had no effects. The delayed time dependent effect of IL-4 might be partially explained by the induction of IL-4 receptor alpha-chain mRNA expression by IL-1beta. Therefore, we conclude that IL-10 and dexamethasone have rapid immunosuppressive effects on the astrocyte response to IL-1beta stimulation, whereas IL-4, which has a delayed action, acts as an immune inducer.

A novel mutant gammac chain from a patient with typical phenotype of X-linked severe combined immunodeficiency (SCID) has partial signalling function for mediating IL-2 and IL-4 receptor action

Mutations of the common gamma (gammac) chain result in X-linked SCID (X-SCID), which is characterized by the reduction in number or absence of peripheral blood T cells and natural killer (NK) cells, with retention of normal numbers of B cells. In the present study we describe a novel mutant gammac chain of an X-SCID patient with a typical X-SCID phenotype. This mutant receptor subunit is able to associate with Jak3 to transduce a weak signal. The Jak3-specific action is demonstrated by the induction of gene expression through the haematopoietin receptor response element (HRRE) by IL-2 and IL-4 in the experimental model of transiently transfected hepatoma cells over-expressing Jak3. This result suggests that a threshold in the gammac-Jak3 interaction determines the X-SCID phenotype.

Functional Role of Interleukin-4 (IL-4) and IL-7 in the Development of X-Linked Severe Combined Immunodeficiency

X-linked severe combined immunodeficiency (X-SCID) is characterized by an absent or diminished number of T cells and natural-killer (NK) cells with a normal or elevated number of B cells, and results from mutations of the γc chain. The γc chain is shared by interleukin-2 (IL-2), IL-4, IL-7, IL-9, and IL-15 receptors. Recently, a survival signal through the IL-7 receptor  (IL-7R) chain was shown to be important for T-cell development in mice and was suggested to contribute to the X-SCID phenotype. In the present study, we examined function of a mutant γc chain (A156V) isolated from an X-SCID patient and found that T cells expressing the mutant γc chain were selectively impaired in their responses to IL-4 or IL-7 compared with the wild-type γc chain expressing cells although responses to IL-2 or IL-15 were relatively maintained. The result shows that IL-4– and/or IL-7–induced signaling through the γc chain is critical for T-cell development and plays an important role in the development of the X-SCID phenotype.

Functional Role of Interleukin-4 (IL-4) and IL-7 in the Development of X-Linked Severe Combined Immunodeficiency

X-linked severe combined immunodeficiency (X-SCID) is characterized by an absent or diminished number of T cells and natural-killer (NK) cells with a normal or elevated number of B cells, and results from mutations of the γc chain. The γc chain is shared by interleukin-2 (IL-2), IL-4, IL-7, IL-9, and IL-15 receptors. Recently, a survival signal through the IL-7 receptor  (IL-7R) chain was shown to be important for T-cell development in mice and was suggested to contribute to the X-SCID phenotype. In the present study, we examined function of a mutant γc chain (A156V) isolated from an X-SCID patient and found that T cells expressing the mutant γc chain were selectively impaired in their responses to IL-4 or IL-7 compared with the wild-type γc chain expressing cells although responses to IL-2 or IL-15 were relatively maintained. The result shows that IL-4– and/or IL-7–induced signaling through the γc chain is critical for T-cell development and plays an important role in the development of the X-SCID phenotype.

Functional and physical association of a cell surface phospholipid and interleukin-2 receptor p55(alpha) subunits

A phosphatidylcholine-like phospholipid expressed in the outer leaflet of the cell membrane shortly after mitogenic activation of T-cells is described, based on the binding of monoclonal antibody 90. 60.3. Expression of the 90.60.3 phospholipid antigen in T-cells is activation-dependent. Once expressed, the 90.60.3 phospholipid is in direct physical association with the interleukin-2 (IL-2) binding domain of IL-2 receptor alpha subunits, but does not affect IL-2 binding. The association is specific, because the 90.60.3 phospholipid is not found in association with other domains of IL-2 receptor alpha subunits, or near IL-2 receptor beta or gamma subunits. Culturing cytokine-dependent cell lines in the presence of monoclonal antibody 90.60.3 potentiates IL-2-dependent cell survival and proliferation in a dose-dependent manner. In contrast, IL-4-dependent responses are not potentiated. Taken together, the data suggest that specific plasma membrane phospholipids expressed in the outer leaflet after T-cell activation associate with the IL-2 binding domain of IL-2 receptor alpha subunits (and perhaps other cytokine receptors), and may play a role in regulating receptor mobility or signal transduction.

Altered cytokine (receptor) mRNA expression as a tool in immunotoxicology

Molecular immunotoxicology is aimed at analysing exposure effects on the temporal expression of important immunoregulatory genes. Cytokines play key roles in the immune system and thus molecular immunotoxicology has focused on the analysis of cytokine (expression) levels. These targets offer important new avenues to explore both in terms of mechanistic understanding of immunotoxicity and in terms of developing new assays and tests for predicting the immunotoxic potential of novel compounds. Effects on cytokine levels can be analysed on two different levels, these being mRNA and protein. The choice essentially depends on the aim of the study. Proteins comprise the biological activity so they are a more direct measure than mRNA. mRNA on the other hand, measures at a specific point in time within a tissue or organ, whereas protein is measured in a body fluid, possibly as a spill-over from tissue, or in a supernatant as a summation over a culture period. mRNA levels are assayed using Northern or dot blotting that both comprise hybridisation and using reverse transcription-polymerase chain reaction (RT-PCR). Although the latter technique has both enormous sensitivity and relative ease of operation as important advantages, it requires much more effort in terms of quantitation. References to the nucleic acid sequences of human, murine, and rat cytokines and their receptors are presented (with accession numbers). Examples in which molecular techniques were successfully employed to assess immunotoxicity and (in some cases) understand mechanisms of action are also presented.

Molecular cloning of the cDNA coding sequence of IL-2 receptor-gamma (gammac) from human and murine forebrain: expression in the hippocampus in situ and by brain cells in vitro

IL-2 has been implicated in various neurobiological processes of the mammalian CNS. To understand how IL-2 acts in the brain, our lab has sought to determine the molecular pharmacological characteristics of brain IL-2 receptors (IL-2R). The lymphocyte IL-2Rgamma, an essential subunit for IL-2 signaling, is also a common subunit (gammac) for multiple immune cytokine receptors (e.g., IL-4R, IL-7R, IL-9R, IL-15R). Having previously cloned the alpha and beta subunits of the IL-2R heterotrimer complex from normal murine forebrain, we examined the hypothesis that the brain IL-2Rgamma is derived from the same or a closely related gene coding sequence as that expressed by lymphocytes. In this study, we cloned and sequenced the full-length IL-2Rgamma coding region from saline-perfused mouse forebrain and from a human hippocampal library. The cDNA sequences of IL-2Rgamma from human and murine brain were 100% homologous to their lymphocyte sequences. Northern blot analysis showed that the mRNA transcripts in murine brain were the expected size, but the predominant transcript expressed in the brain was different than in the spleen. Compared to the spleen, very low levels of IL-2Rgamma were expressed in the forebrain. In the murine hippocampus, a region where a number of neurobiological actions of IL-2 have been reported, IL-2Rgamma mRNA was detected over the dentate gyrus and CA1-CA4 by in situ hybridization histochemistry. IL-2Rgamma was found to be constitutively expressed by murine HN33.dw hippocampal neuronal cells, murine NB41A3 neuroblastoma cells, astrocyte-enriched mixed glial cell cultures, and in SCID mouse forebrain. The human cortical neuronal cell lines, HCN-1A and HCN-2, did not express the IL-2Rgamma gene. These data suggest the possibility that, in addition to being essential in IL-2 signaling in brain, IL-2Rgamma could be a common subunit (gammac) for multiple cytokine receptors which may be operative in the mammalian CNS.

Mouse macrophage development in the absence of the common gamma chain: defining receptor complexes responsible for IL-4 and IL-13 signaling

The common gamma chain (gamma c) forms a critical component of the receptors for interleukins (IL)-2, IL-4, IL-7, IL-9, and IL-15. We analyzed gamma c-deficient mice to define a role for gamma c signaling in the development and function of the macrophage lineage. No major differences in absolute cell numbers, cell surface phenotype, or in vitro function of gamma c- compared to gamma c+ macrophages were observed. We therefore conclude that signaling through the gamma c chain is not essential for the differentiation of mouse macrophages. Although B and T cells require gamma c for IL-4 responses, IL-4 up-regulated major histocompatibility class II molecules and inhibited nitric oxide production from gamma c- macrophages following stimulation with lipopolysaccharide and interferon-gamma. gamma c- macrophages could also respond to IL-13, consistent with the model of a type II IL-4 receptor alpha/IL-13R which can function in the absence of gamma c. Both IL-4 and IL-13 responses could be completely inhibited with the mouse IL-4 antagonist OY, suggesting that all of the observed IL-13 responses pass through the type II receptor, making it the primary signaling receptor complex for IL-13 in mouse macrophages.

Induction of interleukin-2 receptor alpha gene by delta9-tetrahydrocannabinol is mediated by nuclear factor kappaB and CB1 cannabinoid receptor

Previously, we reported that the cannabinoid delta9-tetrahydrocannabinol (THC) increased the expression of interleukin-2 (IL-2) receptor (R) alpha and beta proteins and mRNAs in NKB61A2 cells, but decreased the level of the gamma-chain message. The drug increased beta-chain message stability rather than increased transcription. In the present study, we examined the mechanism responsible for the drug-induced increase in alpha-chain message in NKB61A2 cells. Nuclear run-on and mRNA stability studies showed THC increased the level of alpha gene transcription but had no effect on mRNA stability. Because expression of this gene is regulated by nuclear factor (NF)-kappaB, we next tested the drug effect on the nuclear level of this protein using the electromobility shift assay. These studies showed a drug-induced increase in NF-kappaB activity. To link the increased nuclear factor activity with the THC-induced increase in IL-2R alpha message, antisense oligodeoxynucleotides were used to inhibit expression of the RelA component of NF-kappaB. These results showed anti-RelA antisense eliminated the cannabinoid-induced upregulation of both alpha mRNA and RelA protein. Furthermore, inhibition of the cannabinoid receptor type 1 with antisense oligomers also eliminated the drug effect on the alpha message. These results suggest that THC treatment of NKB61A2 cells increases IL-2R alpha gene transcription by increasing the nuclear level of NF-kappaB through a mechanism involving cannabinoid receptor type 1 expression.

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.

Characterization of interleukin-15 (IL-15) and the IL-15 receptor complex

IL-15 interacts with a heterotrimeric receptor that consists of the beta and gamma subunits of the IL-2 receptor (IL-2R) as well as a specific, high-affinity IL-15-binding subunit, which is designated IL-15R alpha. Since both the beta and the gamma subunits of the IL-2R are required for signaling by either IL-2 or IL-15, it is not surprising that these cytokines share many activities in vitro. However, the differential expression of these cytokines and the alpha chains of their receptors within various tissues and cell types suggests that IL-2 and IL-15 may perform at least partially distinct physiological functions. The production of IL-15 by macrophages, and possibly other cell types, in response to environmental stimuli and infectious agents suggests that IL-15 may play a role in protective immune responses, allograft rejection, and the pathogenesis of autoimmune diseases.

B7-1 synergizes with interleukin-12 in interleukin-2 receptor alpha expression by mouse T helper 1 clones

Expression of interleukin-2 receptor alpha (IL-2R alpha) is critical to induce interleukin (IL)-2-dependent proliferation of T helper (Th)1 clones. The IL-2R alpha expression of Th1 clones is known to be up-regulated by IL-12. Co-stimulation via CD28/CTLA-4 is also known to be important for efficient activation of CD4+ T cells. In the present experiments, IL-12-induced enhancement of IL-2R alpha expression of Th1 clones stimulated with B cells as antigen-presenting cells (APC) is suppressed by the addition of anti-B7-1. To analyze the mechanism, Th1 clones were stimulated with immobilized anti-CD3 plus IL-12 in the presence or absence of Chinese hamster ovary cells that express mouse B7-1 (B7-1CHO) and the enhancement of IL-2R alpha expression induced by the co-stimulation was analyzed. The results of these experiments indicate that B7-1 synergizes with IL-12 in IL-2R alpha expression of the Th1 clone stimulated with anti-CD3, although B7-1CHO alone did not enhance IL-2R alpha expression of the clones. B7-1 stimulation is not mediated by the enhancement of IL-2 production: B7-1 enhancement of IL-2R alpha expression was FK506 resistant, while the inclusion of FK506 abrogated IL-2 production of the Th1 cells. B7-1 co-stimulation did not stabilize IL-2E alpha mRNA, but did synergize with IL-12 to enhance IL-2R alpha mRNA transcription.

Expression of the common cytokine receptor gamma chain by murine dendritic cells including epidermal Langerhans cells

The common cytokine receptor gamma chain (gamma c) is an indispensable component of interleukin (IL)-2, IL-4, IL-7, IL-9, and IL-15 receptors, and its expression has been detected in several leukocyte populations, including T cells, B cells, monocytes, natural killer cells, and neutrophils. The purpose of this study was to determine whether gamma c receptors are expressed by dendritic cells (DC). Constitutive gamma c mRNA expression was observed by reverse transcription polymerase chain reaction and/or Northern blotting for: (a) Ia+ epidermal Langerhans cells (LC), (b) 4F7+ splenic DC, (c) granulocyte/macrophage colony-stimulated factor-propagated bone marrow-derived DC, and (d) the epidermal-derived DC line, XS52, which retains important functions of epidermal LC. Exposure of XS52 cells to recombinant IL-4 induced a rapid up-regulation of c-myc mRNA expression, and this IL-4-dependent signaling was blocked almost completely by anti-gamma c monoclonal antibody (mAb) TUGm2 in a soluble form. Moreover, c-myc up-regulation was inducible in XS52 cells by the same mAb in an immobilized form. These results imply that molecules recognized by this antibody (i.e. gamma c receptors) are expressed on XS52 cell surfaces. We thus conclude that DC express functional gamma c receptors, which then mediate cytokine-dependent regulation of DC functions.

Lack of intermediate-affinity interleukin-2 receptor in mice leads to dependence on interleukin-2 receptor alpha, beta and gamma chain expression for T cell growth

An interleukin (IL)-4 dependent mouse T cell clone 8.2 derived from an IL-2-dependent T cell line was characterized. As measured by flow cytometric analysis and Northern blotting, it expresses IL-2 receptor beta (IL-2R beta) and gamma (IL-2R gamma) chains, but has lost expression of IL-2 receptor alpha chain (IL-2R alpha). To investigate the properties of the mouse IL-2R beta gamma complex and the role of IL-2R alpha gene expression, this clone was further studied. T cell clone 8.2 has lost the capacity to bind 125I-labeled human IL-2 under experimental conditions able to detect intermediate-affinity IL-2R in human cells. Mouse IL-2 is unable to block the binding of mAb TM beta 1 to 8.2 cells. Under the same experimental conditions, mouse IL-2 blocks the binding of TM beta 1 to C30-1 cells expressing the IL-2 alpha beta gamma complex. Since TM beta 1 recognizes an epitope related to the IL-2 binding site of IL-2R beta, these results can be taken as a demonstration that mouse IL-2R beta gamma does not bind mouse IL-2. Furthermore, T cell clone 8.2 does not proliferate in response to recombinant mouse or human IL-2. On the other hand, T cell transfectant lines expressing heterospecific receptors made of the human IL-2R beta and mouse IL-2R gamma chains bind 125I-labeled human IL-2 and proliferate in response to IL-2. This establishes the difference between mouse and human IL-2R beta chains. Transfection of T cell clone 8.2 with human IL-2R alpha genes restores their capacity to proliferate in response to IL-2. In addition, all transfectants grown in IL-2 express the endogeneous mouse IL-2R alpha chain. When grown in IL-4, the endogeneous mouse IL-2R alpha gene remains silent in all these transfectants. These results show that, contrary to the human, the mouse does not express an intermediate-affinity IL-2R. Expression of the IL-2R alpha gene is therefore required for the formation of the functional IL-2R in mice.

Functional characterization of the human interleukin-15 receptor alpha chain and close linkage of IL15RA and IL2RA genes

Interleukins-2 and -15 (IL-2 and IL-15) are cytokines with overlapping but distinct biological effects. Their receptors share two subunits (the IL-2R beta and -gamma chains) that are essential for signal transduction. The IL-2 receptor requires an additional IL-2-specific alpha subunit for high affinity IL-2 binding. Recently, a murine IL-15-specific alpha subunit was identified, cloned, and shown to be structurally related to IL-2R alpha. However, the murine IL-15R alpha alone bound IL-15 with a 1000-fold higher affinity than that seen with IL-2R alpha and IL-2. We now extend these studies into the human system with the isolation of three differentially spliced human IL-15R alpha variants that are all capable of high affinity binding of IL-15. The cytoplasmic domain of IL-15R alpha, like that of IL-2R alpha, is dispensable for mitogenic signaling, suggesting that the primary role of the alpha chains is to confer high affinity binding. At high concentrations, IL-15, like IL-2, is able to signal through a complex of IL-2R beta and -gamma in the absence of the alpha subunit. Furthermore, the IL15RA and IL2RA genes have a similar intron-exon organization and are closely linked in both human and murine genomes. However, the distribution of expression of the IL-15R alpha is much wider than that of the IL-2R alpha, suggesting a broader range of cellular targets for IL-15.

Interleukin (IL)-15 promotes the growth of murine epidermal gamma delta T cells by a mechanism involving the beta- and gamma c-chains of the IL-2 receptor

Dendritic epidermal T cells (DETC) are skin-specific members of the epithelial gamma delta T-cell family in mice. We have reported previously that the growth of DETC is promoted by interleukin (IL)-2 in an autocrine fashion, or by IL-7, which is secreted by neighboring keratinocytes. Here we report that DETC growth is promoted by IL-15, a newly discovered T-cell growth factor that is produced in lymphoid as well as nonlymphoid tissues. Recombinant IL-15 promoted the growth of the 7-17 DETC line in a time- and dose-dependent fashion. Using monoclonal antibodies against alpha-, beta-, or gamma c-chains of the IL-2 receptor complex, we observed that the combination of anti-beta chain and anti-gamma c chain antibodies blocked IL-15 responsiveness completely, whereas anti-alpha chain had no effect. These results indicate that this gamma delta T-cell line uses the beta/gamma c heterodimer for proliferative responses to IL-15. Antibodies against IL-2 or IL-7 did not block IL-15-driven proliferation of 7-17 DETC, indicating that IL-15 promotes their growth in an IL-2- and IL-7-independent manner. Both the surface expression of beta/gamma c heterodimers and the IL-15 responsiveness of 7-17 DETC were highest 1 to 8 days after concanavalin A stimulation, and both declined substantially 21 days after stimulation, illustrating regulation by the state of cell activation. Working with epidermal cells that were freshly procured from CBA mice, we noted that IL-15 promoted conavalin-A-triggered growth of Thy-1+ cells (i.e., DETC), but not of the Thy-1- cells. The gamma c-chain was not expressed by freshly procured DETC, becoming detectable within 48 h after concanavalin A stimulation. We propose that IL-15 facilitates the growth of epithelial gamma delta T cells by a beta/gamma c receptor-dependent mechanism.

Different human interleukin-4 mutants preferentially activate human or murine common receptor gamma chain

Interleukin-4 (IL-4) shows species-specific activity due to species-restricted interaction with the IL-4 receptor alpha (IL-4R alpha) chain. The second subunit of a functional IL-4 receptor, the common gamma chain (gamma c), is more promiscuous, since human IL-4 is able to activate IL-4 receptor complexes containing either human or murine common gamma receptor chain (gamma c). We have stably transfected factor-dependent mouse cells of myeloid and lymphoid origin with combinations of human IL-4R alpha and gamma c derivatives. In these cell lines, both human and murine gamma c receptors as well as IL-4R alpha chains from both species are simultaneously expressed. Both versions of gamma c readily form ternary complexes with either human IL-4 and human IL-4R alpha or murine IL-4 and murine IL-4R alpha. Due to distinct ligand-binding properties of human and murine gamma c, the two receptor complexes can be activated preferentially by different mutant variants of human IL-4. The contribution of murine common gamma chain to human IL-4-induced signal transduction is suppressed by an inhibitory antibody directed to the extracellular domain of the mouse gamma c. We present evidence that the two IL-4R complexes functionally interfere with each other and compete for response-limiting signalling components.

Differences in the interleukin-2 (IL-2) receptor system in human and mouse: alpha chain is required for formation of the functional mouse IL-2 receptor

Reconstitution with mouse interleukin-2 (IL-2) receptor subunits demonstrated that the mouse IL-2 receptor complex was different from the human complex in the alpha chain requirement for the functional mouse receptor complex. The heterotrimeric complex of the mouse exogenous alpha and beta chains and the endogenous gamma chain on mouse lymphoid BW5147 cells showed the ability to bind IL-2 with high affinity, resulting in IL-2-induced tyrosine phosphorylation of a cytosolic tyrosine kinase, JAK3, which is involved in IL-2-dependent signals. Exogenous introduction of the beta chain with the endogenous gamma chain, however, could neither confer appreciable IL-2 binding nor IL-2-induced signal transduction on BW5147 cells, unlike the human beta gamma heterodimer. Mouse spleen CD8+ cells, not having the alpha chain initially, showed IL-2-dependent cell proliferation only when expression of the alpha chain was induced. Collectively, these results illustrate that the functional mouse IL-2 receptor complex necessarily includes the alpha chain, and that the regulation of CD8+ T cell growth during immune reaction depends upon alpha chain expression.

Interleukin-2 as a neuroregulatory cytokine

Interleukin-2 (IL-2), the cytokine also known as T-cell growth factor, has multiple immunoregulatory functions and biological properties not only related to T-cells. In the past decade, substantial evidence accumulated to suggest that IL-2 is also a modulator of neural and neuroendocrine functions. First, extremely potent effects of IL-2 on neural cells were discovered, including activities related to cell growth and survival, transmitter and hormone release and the modulation of bioelectric activities. IL-2 may be involved in the regulation of sleep and arousal, memory function, locomotion and the modulation of the neuroendocrine axis. Second, the concept that IL-2 could act as a neuroregulatory cytokine has been supported by reports on the presence in rodent and human brain tissues of IL-2-like bioactivity, IL-2-like immunoreactivity, IL-2-like mRNA, IL-2 binding sites, IL-2 receptor (IL-2R alpha) and beta chain mRNA and IL-2R immunoreactivity. IL-2 and/or IL-2R molecules mainly localize to the frontal cortex, septum, striatum, hippocampal formation, hypothalamus, locus coeruleus, cerebellum, the pituitary and fiber tracts, such as the corpus callosum, where they are likely expressed by both neuronal and glial cells. Although the molecular biology of the brain IL-2/IL-2R system (including its relation to IL-15/IL-15R alpha) is not yet fully established by cloning and complete sequencing of all respective components, similarities (and to some extent differences) to peripheral counterparts are now apparent. The ability of IL-2 to readily penetrate the blood-brain barrier further suggests that this cytokine could regulate interactions between peripheral tissues and the central nervous system. Taken together, these data suggest that IL-2 of either immune and CNS origin can have access to functional IL-2R molecules on neurons and glia under normal conditions. Additionally, dysregulation of the IL-2/IL-2 receptor system could lead or contribute to functional and pathological alterations in the brain as in the immune system. Understanding the neurobiology of the IL-2/IL-2 receptor system should also help to explain neurologic, neuropsychiatric and neuroendocrine side effects occurring during IL-2 treatment of peripheral and brain tumors. Immunopharmacological manipulation either aiming at the activation or suppression of IL-2 signaling should consider functional interference with constitutive and inducible IL-2 receptors on brain cells in order to fulfil the high expectations associated with the use of this cytokine as a promising agent in immunotherapies, especially of brain tumors.

Identification and cloning of a novel IL-15 binding protein that is structurally related to the alpha chain of the IL-2 receptor

Interleukin-15 (IL-15) is a novel cytokine of the four-helix bundle family which shares many biological activities with IL-2, probably due to its interaction with the IL-2 receptor beta and gamma (IL-2R beta and gamma c) chains. We report here the characterization and molecular cloning of a distinct murine IL-15R alpha chain. IL-15R alpha alone displays an affinity of binding for IL-15 equivalent to that of the heterotrimeric IL-2R for IL-2. A biologically functional heteromeric IL-15 receptor complex capable of mediating IL-15 responses was generated through reconstruction experiments in a murine myeloid cell line. IL-15R alpha is structurally similar to IL-2R alpha; together they define a new cytokine receptor family. The distribution of IL-15 and IL-15R alpha mRNA suggests that IL-15 may have biological activities distinct from IL-2.

Non random activation of endogenous interleukin-2, (IL-2), IL-2 receptor alpha and IL-2 receptor beta genes after transfection of mouse fibroblasts with a cDNA for the alpha chain of the human IL-2 receptor

Mouse fibroblasts do not ordinarily express components for the interleukin-2 receptor (IL-2R alpha, beta, and gamma). An analysis of these cells by reverse transcription followed by polymerase chain reaction, however, indicates the presence of transcripts specific for the IL-2R beta and gamma genes. Transfection of the cDNA for the alpha chain of the human IL-2R into LTK- mouse fibroblast cell line (L3 cells) leads, in long-term cultures, to the formation of transcripts of endogenous mouse IL-2, IL-2R alpha and beta genes, as detected by Northern blotting. Based upon the results of the binding of 125I-labeled IL-2 to the transfected cells, three IL-2-binding proteins of 55 kDa, 65 kDa and 75 kDa were expressed by the transfected cells. The 65-kDa and 75-kDa proteins bound IL-2 in the presence of monoclonal antibodies for the IL-2R alpha chain. These polypeptides assembled to form high-affinity IL-2R, as shown by Scatchard binding analyses. The receptors were functionally active, since the expression of H-2k major histocompatibility complex antigens on the surface membranes of L3 cells was enhanced by exposing the cells to IL-2. Activation of the IL-2 gene was also observed in long-term cultures of L alpha beta cells, another LTK- transfectant expressing the human IL-2R alpha chain. This type of gene activation was not observed in LTK- fibroblasts transfected with cDNA for human IL-2 or IL-2R beta genes. In L3 and L alpha beta cells, transcription of the endogenous IL-2 gene was suppressed by cyclosporin A and enhanced by cycloheximide. These data may have implications for gene therapy of cancer cells.

Species-specific agonist/antagonist activities of human interleukin-4 variants suggest distinct ligand binding properties of human and murine common receptor gamma chain

Interleukin-4 (IL-4) is a pleiotropic cytokine eliciting various responses in target cells upon binding to its receptor. Activation of the IL-4 receptor probably involves interaction of the ligand with both the IL-4 receptor alpha subunit (IL-4R alpha) and the common gamma chain (c gamma). Although human and murine IL-4 receptor alpha chains are specific for IL-4 from the same species, murine c gamma can form a signal-competent complex with human IL-4R alpha (hIL-4R alpha) and human IL-4 (hIL-4). We have generated a hIL-4 responsive murine myeloid cell line (FDC-4G) expressing a chimera comprising the extracellular domain of human IL-4R alpha and the intracellular domain of human granulocyte colony-stimulating factor receptor (hG-CSFR). This hybrid receptor was shown to form a complex with hIL-4 and the murine c gamma-chain. Biological activities of human IL-4 variants on murine FDC-4G cells and on the human erythroleukemic cell line TF-1 displayed a strikingly different pattern. Single amino acid replacements at two different positions in the C-terminal helix of hIL-4, the region of the previously defined "signaling site," lead to an inverse agonist/antagonist behavior of the resulting cytokines in the two cellular systems. From these findings we conclude that upon formation of the activated IL-4 receptor complex murine and human c gamma interact with hIL-4 in a geometrically different fashion.

Involvement of the interleukin-2 receptor gamma subunit in interleukin-4-dependent activation of mouse hematopoietic cells and splenic B cells

Interleukin-4 (IL-4) has various activities on B cells and on hematopoietic cells. We previously reported that TUGm2, a monoclonal antibody to the gamma subunit of the IL-2 receptor (IL-2R gamma), inhibited IL-4-dependent proliferation of CTLL2, a cytotoxic T cell line. We proposed that IL-2R gamma is required for the functional IL-4 receptor (IL-4R) in T cells. In the present work, we further examined whether or not IL-2R gamma is involved in IL-4R function in mouse myeloid cell lines and splenic B cells. TUGm2 suppressed the IL-4-induced proliferation of BA/F3 or IC2 cells, as well as of purified splenic B cells. TUGm2 partially suppressed proliferation of B cells induced by the combination of IL-4 and anti-immunoglobulin M (IgM) antibody. In contrast, TUGm2 had no effect on proliferation of B cells induced by anti-IgM antibody alone or lipopolysaccharide (LPS). TUGm2 also inhibited IgE production induced by IL-4 of LPS-stimulated B cells. The induction of major histocompatibility complex class II molecules or CD23 by IL-4 was virtually unaffected by TUGm2 antibody. These results indicate that IL-2R gamma is differentially involved in various IL-4-dependent reactions.

Expression of interleukin-2 receptor gamma on human monocytes: characterization of lineage specific post-translational modifications

Functional interleukin-2 receptors (IL-2R) on lymphocytes contain both IL-2R beta and gamma chains. Whereas constitutive expression of IL-2R beta has been found on monocytes, the expression of IL-2R gamma on these phagocytes has not been examined. We performed reverse-transcription-polymerase chain reaction with Southern blot analysis on RNA derived from purified human monocytes and discovered that they constitutively produce IL-2R gamma mRNA. Western immunoblotting revealed 58- and 64-kDa forms of IL-2R gamma on YT-1 and human monocytes, whereas 58-, 64-, and 69-kDa bands were detected using peripheral blood mononuclear cells and non-adherent lymphocytes. These different forms resulted from variable N-linked glycosylation since culture of the cells in tunicamycin resulted in detection of a single 39-kDa band which corresponds to the molecular weight predicted from the deduced amino acid sequence. By co-immunoprecipitation, the IL-2R beta subunit associates with only the 64-kDa IL-2R gamma protein band in monocytes.

Expression of the mouse interleukin-2 receptor gamma chain in various cell populations of the thymus and spleen

Expression of the gamma chain, which is shared among functional receptor complexes for interleukin (IL)-2, IL-4 and IL-7, was examined with hematopoietic cells in mouse thymus and spleen by flow cytometry. The gamma chain was expressed in cell populations from the spleen. Stimulation with concanavalin A and lipopolysaccharide caused fluctuation in expression of the gamma chain in T and B cells, respectively. T lineage cells developing in the adult thymus expressed the gamma chain. Fetal thymus at day 15 contained mostly immature thymocytes, which also expressed the gamma chain. These results demonstrate that the gamma chains is widely expressed in T lineage cells, probably indicating that the gamma chain plays a role not only in the proliferation of mature hematopoietic cells but also in the development of immature cells through signal transduction as a common receptor subunit for multiple cytokines.

Utilization of the beta and gamma chains of the IL-2 receptor by the novel cytokine IL-15

We have recently cloned a novel cytokine, IL-15, with shared bioactivities but no sequence homology with IL-2. We found high affinity IL-15 binding to many cell types, including cells of non-lymphoid origin. Analysis of IL-15 interaction with subunits of the IL-2 receptor (IL-2R) revealed that the alpha subunit was not involved in IL-15 binding. We demonstrated directly in cells transfected with IL-2R subunits that both the beta and gamma chains are required for IL-15 binding and signaling. Hence, IL-15, like IL-2, IL-4 and IL-7, utilizes the common IL-2R gamma subunit found to be defective in X-linked severe combined immunodeficiency in humans. IL-15 is the only cytokine other than IL-2 that has also been shown to share the beta signaling subunit of IL-2R. The differential ability of some cells to bind and respond to IL-2 and IL-15 implies the existence of an additional IL-15-specific component.

Heterodimerization of the IL-2 receptor beta- and gamma-chain cytoplasmic domains is required for signalling

The interaction of interleukin-2 (IL-2) and IL-2 receptors critically regulates the T-cell immune response following antigen activation. IL-2 can signal through high or intermediate affinity receptors which contain IL-2R alpha (refs 3, 4) +beta (refs 5-8) +gamma (ref. 9) or beta+gamma chains, respectively. IL-2R gamma is a common gamma chain, gamma c, also shared by the IL-7 (ref. 10) and IL-4 (refs 11, 12) receptors, which when mutated results in X-linked severe combined immunodeficiency. Using chimaeric receptor constructs together with monoclonal or bispecific antibodies we demonstrate here that IL-2 signalling requires ligand-induced extracellular-domain-mediated heterodimerization of the beta- and gamma c-chain cytoplasmic domains. Anti-IL-2R alpha monoclonal antibodies trigger proliferation of cells transfected with chimaeric constructs in which the extracellular domains of IL-2R beta and gamma c are replaced by that of IL-2R alpha. Other experiments using chimaeric constructs indicated that IL-2 binds monomerically and monovalently to IL-2R alpha and that the beta-transmembrane domain is not required for receptor chain interactions. Finally, we provide a method for mapping residues in the gamma c cytoplasmic domain even in cells that constitutively express gamma c.

The molecular basis of X-linked severe combined immunodeficiency: the role of the interleukin-2 receptor gamma chain as a common gamma chain, gamma c

X-linked severe combined immunodeficiency is characterized by severe and persistent infections from early life resulting from profound impairment of both cellular and humoral immune function. XSCID is characterized by an absence or diminished number of T cells and histologic evidence of hypoplastic and abnormal differention of the thymic epithelium. The discovery that this disease results from the mutations of the IL-2R gamma chain was surprising since IL-2-deficient mice and human SCID patients had milder phenotypes. This led to the speculation that IL-2R gamma would prove to be a common gamma chain, gamma c, which would play important roles in other cytokine receptors in addition to the IL-2 receptor. There is now compelling evidence to support a role in at least two other cytokine receptors, namely the IL-4 and IL-7 receptors. Thus, with inactivation of gamma c, multiple cytokine systems are simultaneously affected, resulting in the profoundly impaired phenotype of XSCID. It is possible and even likely that gamma c will be found to be a functional component of additional receptors as well. These findings have resulted in a significant improvement in our understanding of the pathophysiologic development of the defects in XSCID and also have important ramifications for prenatal and postnatal diagnosis, carrier female identification, and gene therapy for XSCID.

Functional participation of the IL-2 receptor gamma chain in IL-7 receptor complexes

The gamma chain of the interleukin-2 (IL-2) receptor is shared with the functional IL-4 receptor and is causatively related to X-linked severe combined immunodeficiency (XSCID), which is ascribed to a profound T cell defect. Studies with monoclonal antibodies specific for the IL-2 receptor gamma chain showed that the gamma chain participates in the functional high-affinity receptor complexes for IL-7 that are involved in the differentiation of T and B cells. Participation of the gamma subunit in more than one receptor may enable the elucidation of the mechanisms of XSCID development and lymphocyte differentiation.

Sharing of the interleukin-2 (IL-2) receptor gamma chain between receptors for IL-2 and IL-4

The gamma chain of the interleukin-2 (IL-2) receptor is an indispensable subunit for IL-2 binding and intracellular signal transduction. A monoclonal antibody to the gamma chain, TUGm2, inhibited IL-2 binding to the functional IL-2 receptors and also inhibited IL-4-induced cell growth and the high-affinity binding of IL-4 to the CTLL-2 mouse T cell line. Another monoclonal antibody, TUGm3, which reacted with the gamma chain cross-linked with IL-2, also immunoprecipitated the gamma chain when cross-linked with IL-4. These results suggest that the IL-2 receptor gamma chain is functionally involved in the IL-4 receptor complex.