A bioassay for the measurement of human interleukin-4

Chimeric Antigen Receptors Based on Low Affinity Mutants of FcεRI Re-direct T Cell Specificity to Cells Expressing Membrane IgE

IgE is the key mediator of allergic responses. Omalizumab, an IgE-specific monoclonal antibody that depletes IgE, is effective for treating severe allergic asthma. The need for frequent administration of the expensive drug, however, limits its applications. Taking advantage of T cell memory, adoptive T cell therapy (ACT) targeting IgE-producing cells has the potential to achieve long-term suppression of IgE and relief of symptoms for severe allergic diseases. The transmembrane form of IgE (mIgE), which is present on all IgE-producing cells, serves as an excellent molecular target for ACT that employs chimeric antigen receptors (CARs). Here, we designed and tested CARs that use the extracellular domain of high affinity IgE receptor, FcεRIα, for mIgE recognition. When expressed on Jurkat T cells, FcεRIα-based CARs mediated robust responses in terms of CD69 upregulation to U266 myeloma cells expressing low levels of mIgE. FcεRIα-based CARs specifically recognized cells expressing mIgE, but not cells with secreted IgE captured through Fcε receptors. CAR⁺ Jurkat cells did not respond to LAD2 mast cells with secreted IgE bound through FcεRI or Ramos cells with secreted IgE bound through FcεRII. Co-culture of CAR⁺ Jurkat cells and LAD2 mast cells with IgE bound did not trigger LAD2 cell degranulation. The activity of CAR using wild type FcεRIα for mIgE binding was inhibited by the presence secreted IgE, which likely blocked CAR-mIgE interaction. The activities of CARs using low affinity mutants of FcεRIα, however, tolerated secreted IgE at relatively high concentrations. Moreover, primary human CD8⁺ T cells expressing a low affinity mutant CAR responded to U266 cells with INFγ production and cytotoxicity despite the presence of secreted IgE. The potency, specificity, and robustness of our CAR design, combined with repaid advances in the safety of ACT, hold promise for novel and highly effective cell-based therapies against severe allergic diseases.

Ectopic expression of a novel CD22 splice-variant regulates survival and proliferation in malignant T cells from cutaneous T cell lymphoma (CTCL) patients

CD22 is a member of the Sialic acid-binding Ig-like lectin (Siglec) family of lectins described to be exclusively present in B lymphocytes and B cell-derived neoplasms. Here, we describe a novel splice form of CD22 (designated CD22∆N), which lacks the N-terminal domain as demonstrated by exon-specific RT-PCR and differential recognition by anti-CD22 antibodies. Importantly, CD22∆N mRNA is expressed in skin lesions from 39 out of 60 patients with cutaneous T cell lymphoma (CTCL), whereas few patients (6 out of 60) expresses full-length, wild type CD22 (CD22wt). In addition, IHC staining of tumor biopsies confirmed the expression of CD22 in CD4+ T cells. Moreover, four out of four malignant T cell lines express CD22: Two cell lines express CD22∆N (MyLa2059 and PB2B) and two express CD22wt (MAC-1 and MAC-2A). siRNA-mediated silencing of CD22 impairs proliferation and survival of malignant T cells, demonstrating a functional role for both CD22∆N and CD22wt in these cells.In conclusion, we provide the first evidence for an ectopic expression of CD22 and a novel splice variant regulating malignant proliferation and survival in CTCL. Analysis of expression and function of CD22 in cutaneous lymphomas may form the basis for development of novel targeted therapies for our patients.

Malignant T cells express lymphotoxin α and drive endothelial activation in cutaneous T cell lymphoma

Lymphotoxin α (LTα) plays a key role in the formation of lymphatic vasculature and secondary lymphoid structures. Cutaneous T cell lymphoma (CTCL) is the most common primary lymphoma of the skin and in advanced stages, malignant T cells spreads through the lymphatic to regional lymph nodes to internal organs and blood. Yet, little is known about the mechanism of the CTCL dissemination. Here, we show that CTCL cells express LTα in situ and that LTα expression is driven by aberrantly activated JAK3/STAT5 pathway. Importantly, via TNF receptor 2, LTα functions as an autocrine factor by stimulating expression of IL-6 in the malignant cells. LTα and IL-6, together with VEGF promote angiogenesis by inducing endothelial cell sprouting and tube formation. Thus, we propose that LTα plays a role in malignant angiogenesis and disease progression in CTCL and may serve as a therapeutic target in this disease.

Redirecting cell-type specific cytokine responses with engineered interleukin-4 superkines

Cytokines dimerize their receptors, with binding of the “second chain” triggering signaling. In the interleukin (IL)-4/13 system, different cell types express varying levels of alternative second receptor chains (γc or IL-13Rα1), forming functionally distinct Type-I or Type-II complexes. We manipulated the affinity and specificity of second chain recruitment by human IL-4. A Type-I receptor-selective IL-4 ‘superkine’ with 3700-fold higher affinity for γc was 3-10 fold more potent than wild-type IL-4. Conversely, a variant with high affinity for IL-13Rα1 more potently activated cells expressing the Type-II receptor, and induced differentiation of dendritic cells from monocytes, implicating the Type-II receptor in this process. Superkines exhibited signaling advantages on cells with lower second chain levels. Comparative transcriptional analysis reveals that the superkines induce largely redundant gene expression profiles. Variable second chain levels can be exploited to redirect cytokines towards distinct cell subsets and elicit novel actions, potentially improving the selectivity of cytokine therapy.

Counter-regulation mechanism of IL-4 and IFN-α signal transduction through cytosolic retention of the pY-STAT6:pY-STAT2:p48 complex

IFN-α and IL-4 induce Th1 and Th2 responses, respectively, and often display antagonistic actions against each other. To elucidate the molecular mechanism of counter-regulation, we have investigated the signal interception by IFN-α and IL-4, employing a human B-cell line Ramos, sensitive to both cytokines. In these cells, IFN-α effectively inhibited IL-4-induced Fc epsilon receptor II (CD23) expression, whereas IL-4 suppressed IFN-α-mediated IRF7 expression. The counter-regulatory action by IL-4 and IFN-α proceeded with a delayed kinetics requiring 4 h. Notably, IFN-α did not affect the IL-4-induced tyrosine phosphorylation of STAT6, but induced a time-dependent cytoplasmic accumulation of phosphotyrosine(pY)-STAT6 and a corresponding decrease in nuclear pY-STAT6. By confocal analysis and co-immunoprecipitation assays, we demonstrated the colocalization and molecular interaction of IL-4-induced pY-STAT6 with IFN-α-induced pY-STAT2:p48 in the cytosol. In addition, the over-expression of STAT2 or STAT6 induced the concomitant cytosolic accumulation of pY-STAT6 or pY-STAT2, leading to the suppression of IL-4-induced CD23 or IFN-α-induced IRF7 gene expression, respectively. Our data suggest that the signals ensued by IFN-α and IL-4 induce cytoplasmic sequestration of IL-4-activated STAT6 and IFN-α-activated STAT2:p48 in B cells through the formation of pY-STAT6:pY-STAT2:p48 complex, which provides a novel mechanism by which IFN-α and IL-4 cross-regulate their signaling into the nucleus.

Ectopic expression of B-lymphoid kinase in cutaneous T-cell lymphoma

B-lymphoid kinase (Blk) is exclusively expressed in B cells and thymocytes. Interestingly, transgenic expression of a constitutively active form of Blk in the T-cell lineage of mice results in the development of T-lymphoid lymphomas. Here, we demonstrate nuclear factor-kappa B (NF-kappaB)-mediated ectopic expression of Blk in malignant T-cell lines established from patients with cutaneous T-cell lymphoma (CTCL). Importantly, Blk is also expressed in situ in lesional tissue specimens from 26 of 31 patients with CTCL. Already in early disease the majority of epidermotropic T cells express Blk, whereas Blk expression is not observed in patients with benign inflammatory skin disorders. In a longitudinal study of an additional 24 patients biopsied for suspected CTCL, Blk expression significantly correlated with a subsequently confirmed diagnosis of CTCL. Blk is constitutively tyrosine phosphorylated in malignant CTCL cell lines and spontaneously active in kinase assays. Furthermore, targeting Blk activity and expression by Src kinase inhibitors and small interfering RNA (siRNA) inhibit the proliferation of the malignant T cells. In conclusion, this is the first report of Blk expression in CTCL, thereby providing new clues to the pathogenesis of the disease.

Single nucleotide changes in the human Igamma1 and Igamma4 promoters underlie different transcriptional responses to CD40

Analysis of subclass-specific germline transcription in activated peripheral B cells revealed a highly biased expression pattern of the four Igamma transcripts to signals through CD40 and IL-4. This difference was most pronounced when comparing the profile of Igamma1 and Igamma4 transcripts and was not expected given the very high degree of sequence conservation between promoters. In this report, the influence of sequence differences on the regulation of the Igamma1 and Igamma4 promoters has been investigated given the highly muted transcriptional activity of the Igamma4 promoter. Two regions were analyzed where single nucleotide differences corresponded to major changes in transcriptional activity. These regions were the previously defined CD40 response region containing three putative NF-kappaB-binding sites and the downstream 36-bp region containing CREB/activating transcription factor and kappaB6 sites. Mutation of a single nucleotide at position 6 within the Igamma4 kappaB6 site increased promoter activity to approximately 50% of the activity of the Igamma1 promoter. Furthermore, elevated promoter strength corresponded with increased binding of p50, p65, c-Rel, RelB, and p300 proteins to a level comparable with that of Igamma1. Minor nucleotide changes to both the Igamma4 CD40 response region and the 36-bp element resulted in a response undistinguishable from an Igamma1 response, suggesting cooperation between the two regulatory regions for optimal transcriptional activity. Collectively, these mutational analyses suggest that minor sequence differences contribute to the composition and affinity of transcriptional protein complexes regulating subclass-specific germline transcription, which in part impacts the overall level of class switch recombination to targeted C(H) regions.

A Novel NF-κB-Regulated Site within the Human Iγ1 Promoter Requires p300 for Optimal Transcriptional Activity

Transcriptional activation of germline (GL) promoters occurs through binding of NF-kappaB to three evolutionarily conserved sites within a CD40 response region in the human and mouse GL Igamma and Iepsilon promoters. Here we identify and characterize a novel NF-kappaB binding site (kappaB6) within the human GL Igamma1 promoter that plays an essential role in basal- and CD40-induced transcription. This site is adjacent to identified CREB/activating transcription factor (ATF) sites, present in the Igamma1 but not the Igamma3 promoter, which are important for the amplification of transcription. Our data suggest a cohesive protein complex regulating Igamma1 promoter activity because disruption of any individual NF-kappaB or CREB/ATF site markedly lowers the overall inducible activity of the promoter. In addition, alteration of helical phasing within the promoter indicates spatial orientation of CREB/ATF and NF-kappaB, proteins contributes directly to promoter activity. We found that CREB and p50 transactivators, as well as coactivator p300, interact in vivo with the Igamma1 promoter in the presence and absence of CD40 signaling in Ramos and primary B cells. However, the level of CREB and p300 binding differs as a consequence of activation in primary B cells. Furthermore, overexpression of p300, and not a mutant lacking acetyltransferase activity, significantly increases Igamma1 construct-specific transcription. Together these data support a model whereby CREB and multiple NF-kappaB complexes bind to the Igamma1 promoter and recruit p300. CD40 signals induce p300-dependent changes that result in optimal Igamma1 promoter activity.

Kinetics of the Apoptotic Response Induced by Anti-IgM Engagement of the B Cell Receptor Is Dependent on the Density of Cell Surface Immunoglobulin M Expression

The effect of B cell receptor (BCR) density on anti-BCR-induced apoptosis was assessed in Ramos cell lines, expressing low, medium, or high levels of surface IgM (sIgM(LO), sIgM(MED), sIgM(HI)). All cells required a 6-mug/ml threshold of anti-IgM to elicit apoptosis. Anti-IgM treatment of sIgM(LO) cells induced growth inhibition and limited dose-independent apoptosis. Anti-IgM treatment of sIgM(MED) cells induced dose-independent death with a 32-h lag. Ligation of the BCR in the sIgM(HI) cells induced rapid apoptosis beginning by 6 h, which was dose-dependent. Secondary crosslinking reagents did not affect apoptosis, and this effect was independent of anti-IgM concentration, time, or sIgM density. These results suggest that the response to BCR engagement strongly depends on the cell surface receptor density.

p38 Mitogen-activated protein kinase regulates interleukin-4-induced gene expression by stimulating STAT6-mediated transcription

STAT6 functions as a critical mediator of IL-4-stimulated gene activation, and the function of STAT6 is regulated by both tyrosine and serine kinase activities. Here we analyzed the role of serine phosphorylation in regulation of STAT6-mediated transcription. Optimal transcriptional response of IL-4-inducible promoters requires costimulatory signals through CD40-stimulated intracellular kinases such as p38 MAPK. We found that the p38 MAPK inhibitor SB202190 as well as the dominant negative p38 MAPK inhibited interleukin (IL)-4 regulated expression of CD23 in Ramos B cells. IL-4 stimulation did not stimulate p38 MAPK activity, but inhibition of p38 MAPK activity directly correlated with inhibition of IL-4-induced gene activation. Dissection of individual response elements on IL-4-regulated promoter showed that C/EBP beta-mediated transcription was insensitive to SB202190 treatment in B cells whereas STAT6-mediated transcription was regulated by p38 MAPK. The IL-4-induced immediate activation events of STAT6 were not affected by p38 MAPK activity. Furthermore, phosphoamino acid analysis and phosphopeptide mapping indicated that STAT6 is not a direct substrate for p38 MAPK. Instead, p38 MAPK was found to directly regulate the activity of the transactivation domain of STAT6. These results show that, in addition to the well established proinflammatory effects, p38 MAPK also provides a costimulatory signal for IL-4-induced gene responses by directly stimulating the transcriptional activation of STAT6.

CREB/ATF proteins enhance the basal and CD154- and IL-4-induced transcriptional activity of the human Igamma1 proximal promoter

To understand the underlying basis for the strong IL-4- and CD154-mediated Igamma1 promoter activity in Ramos 2G6 B cells, we carried out transient transfection assays with luciferase-based constructs containing approximately 2.2 kb and 500 bp of the human Igamma1 proximal promoter region. As a comparison, the corresponding regions of the human Igamma3 promoter were tested under identical conditions. We found that both Igamma1 and Igamma3 promoter constructs were activated upon transfection into Ramos B cells and that activity was significantly up-regulated by CD154 and IL-4 signals. However, the Igamma1 promoter was measurably stronger than the Igamma3 promoter with respect to both basal and induced responses. Sequence comparison revealed a divergent 36-bp region containing multiple putative transcription factor binding sites in the Igamma1 but not the Igamma3 promoter. A mutational "swap" of this sequence resulted in a marked decrease and increase in Igamma1 and Igamma3 basal and induced promoter activity, respectively. Gel retardation assays with Igamma1-specific probes revealed CREB-containing complexes that were not observed with the corresponding Igamma3 probes. Mutation of a single nucleotide in overlapping CREB sites in the Igamma1 sequence resulted in a significant decrease in basal activity with a corresponding reduction in the level of IL-4- and CD154-mediated transcription.

Interleukin-4-induced transcriptional activation by Stat6 involves multiple serine/threonine kinase pathways and serine phosphorylation of Stat6

Stat6 transcription factor is a critical mediator of IL-4-specific gene responses. Tyrosine phosphorylation is required for nuclear localization and DNA binding of Stat6. The authors investigated whether Stat6-dependent transcriptional responses are regulated through IL-4-induced serine/threonine phosphorylation. In Ramos B cells, the serine/threonine kinase inhibitor H7 inhibited IL-4-induced expression of CD23. Treatment with H7 did not affect IL-4R-mediated immediate signaling events such as tyrosine phosphorylation of Jak1, Jak3, insulin receptor substrate (IRS)-1 and IRS-2, or tyrosine phosphorylation and DNA binding of Stat6. To analyze whether the H7-sensitive pathway was regulating Stat6-activated transcription, we used reporter constructs containing different IL-4 responsive elements. H7 abrogated Stat6-, as well as Stat5-, mediated reporter gene activation and partially reduced C/EBP-dependent reporter activity. By contrast, IL-4-induced transcription was not affected by wortmannin, an inhibitor of the phosphatidyl-inositol 3′-kinase pathway. Phospho-amino acid analysis and tryptic phosphopeptide maps revealed that IL-4 induced phosphorylation of Stat6 on serine and tyrosine residues in Ramos cells and in 32D cells lacking endogenous IRS proteins. However, H7 treatment did not inhibit the phosphorylation of Stat6. Instead, H7 inhibited the IL-4-induced phosphorylation of RNA polymerase II. These results indicate that Stat6-induced transcription is dependent on phosphorylation events mediated by H7-sensitive kinase(s) but that it also involves serine phosphorylation of Stat6 by an H7-insensitive kinase independent of the IRS pathway.

A polymorphic CD40 ligand (CD154) molecule mediates CD40-dependent signalling but interferes with the ability of soluble CD40 to functionally block CD154:CD40 interactions

We report the characterization of a naturally occurring polymorphism in CD40 ligand (CD40L, CD154) expressed by activated T cells from a young female patient. This polymorphism encodes a nonconservative Gly --> Arg substitution in amino acid 219 in the extracellular, CD40 binding domain of the molecule. Studies carried out with 293 epithelial cells ectopically expressing the polymorphic protein (CD154/G219R) revealed reduced levels of binding to different anti-CD154 monoclonal antibodies (mAb) and CD40-immunoglobulin (CD40-Ig). However, recognition of the polymorphic and wild-type CD154 molecules by a polyclonal antiserum was comparable, suggesting that the polymorphism affects the ability of the protein to interact with CD40 but does not significantly alter its surface expression. To determine if reduced cross-linking of CD40 mediated decreased functional effects, three CD40-dependent properties were measured. We found that pathways leading to the induction of surface CD23, CD80, and Igamma transcription were activated in response to CD154/G219R signalling. However, the decrease in affinity for CD40 by the mutated CD154 affected the ability of CD40-Ig to efficiently interfere with the binding and effectively block induced CD80 expression. In contrast, we found that the 5c8 mAb, which recognized the polymorphic molecule to a similar extent as wild-type CD154, effectively blocked the interaction between CD154/G219R and CD40 as measured by CD80 expression. These findings suggest that naturally occurring polymorphisms in the CD154 molecule may affect the ability of CD40-mediated functions to be blocked by soluble CD40 or anti-CD154 mAb in the therapeutic treatment of disease and graft rejection.

A single gene for human TRAF-3 at chromosome 14q32.3 encodes a variety of mRNA species by alternative polyadenylation, mRNA splicing and transcription initiation

Human TRAF-3 is a signaling molecule that interacts with the cytoplasmic tails of CD40 and other TNF-receptor family members. TRAF-3 mRNA is expressed as two major classes of approximately 2 and 8 kb and a number of TRAF-3 encoding cDNA clones differ in discrete gene segments. Because this variety of mRNA species could result from mRNA processing events and/or multiple genes, the structure and localization of TRAF-3 encoding gene elements were determined. FISH and radiation hybrid mapping demonstrated that TRAF-3 is located at chromosome 14q32.3, approximately 1 Mb centromeric to the Ig heavy chain gene complex. Physical mapping of four overlapping genomic PAC clones established that TRAF-3 transcripts are encoded by a single gene, comprised of 13 exons and spanning 130 kb. Alternative polyadenylation in the mRNA segment encoded by exon 12 accounts for the difference between the 2 kb and the 8 kb classes of transcripts. Alternative mRNA splicing in the coding region (encoded by exons 3-12) generates transcripts which delete exons 8 (75 nt), 7+8 (156 nt) or 8+9 (168 nt) and that encode distinct protein isoforms (delta25, delta52 and delta56 aa, respectively). Alternative splicing of exon 2 (139 nt) and alternative transcriptional initiation result in mRNA species with distinct 5'UTRs. Together, these data indicate that a single TRAF-3 gene encodes a variety of mRNA species by a combination of alternative polyadenylation, alternative mRNA splicing and/or alternative initiation.

Expression, purification, and characterization of recombinant human interleukin-13 from NS-O cells

Interleukin-13 is a cytokine which is secreted by activated T lymphocytes and primarily impacts monocytes, macrophages, and B cells. A synthetic gene coding for human interleukin-13 has been prepared and cloned into expression vector pEE12. The construct was transfected into NS-O cells, which showed stable expression of the recombinant protein. A four-step purification procedure consisting of S-Sepharose, Q-Sepharose, hydroxyapatite, and Sephacryl-100 chromatographies yielded bioactive interleukin-13 of > 98% purity. The purified protein was structurally characterized. The extinction coefficient at 280 nm was determined to be 5678 M-1 cm-1. Amino acid sequencing confirmed that the N-terminus of the purified protein was intact. Electrospray mass spectrometric analysis, size-exclusion chromatography, and SDS-PAGE revealed that the biologically active protein is monomeric and unglycosylated. Mass spectrometry and a chemical assay for free sulfhydryls indicated that the four cysteine residues of interleukin-13 are involved in two intramolecular disulfide bonds. The circular dichroism spectrum confirms that interleukin-13 belongs to the alpha-helical family of cytokines. A biologically inactive covalent trimer also forms in the cell culture, but can be separated from the monomer by the hydroxyapatite and size-exclusion chromatographies. These data indicate that human interleukin-13 retains many structural similarities to human interleukin-4, from which it arose by a gene duplication event.

CD40 Ligand Exerts Differential Effects on the Expression of Iγ Transcripts in Subclones of an IgM+ Human B Cell Lymphoma Line

The CD40:CD40 ligand (CD40L) interaction plays a critical role in T cell-dependent isotype switching. To elucidate the role of CD40 signaling in the activation of γ germline transcription and as an extension, in targeting Cγ regions for isotype switching, an IgM+ Burkitt lymphoma cell line (Ramos 2G6) was assayed for the up-regulation of germline γ transcripts after CD40L stimulation. Independent Ramos 2G6 subclones that either expressed (Iγ+) or did not express (Iγ−) basal levels of Iγ transcripts were assessed for their transcriptional response to CD40L signaling by contact with either a Jurkat T cell line (D1.1) or a transfected CD40L-expressing epithelial cell line (293/CD40L) in the presence or absence of IL-4. Both Iγ− and Iγ+ Ramos 2G6 subclones cultured with IL-4 and CD40L markedly up-regulated germline transcription predominantly from the γ1, γ2, and γ3 subclasses over levels obtained with IL-4 alone. In addition, these two signals were required to obtain de novo switch recombination. However, incubation with CD40L alone resulted in a substantial increase in germline transcription only in the Iγ+ and not the Iγ− subclones. Observed basal transcription at the γ1 locus also correlated with the ability of not only the γ1 locus, but also the γ2 and γ3 loci, to up-regulate germline transcripts in response to CD40 signaling. These data are consistent with CD40:CD40L contact up-regulating germline transcription only after the B cell has received a signal that alters the transcriptional state of the heavy chain locus.

Expression and chromosomal localization of the human alpha 4/IGBP1 gene, the structure of which is closely related to the yeast TAP42 protein of the rapamycin-sensitive signal transduction pathway

To study the function of the B cell signal transduction molecule alpha 4 (IGBP1), we isolated a human alpha 4 (IGBP1) gene that has sequence similarity to the yeast protein (TAP42) involved in the rapamycin-sensitive signal transduction pathway. The human alpha 4 has sequence identities with murine alpha 4 of 83.4% nucleotide and 82.9% amino acid sequence, and a stretch of consensus motifs in the carboxyl terminal is conserved among the related genes of human, mouse, yeast, and rice. The gene is expressed as a 1.4-kb mRNA in the spleen, lymph node, thymus, appendix, peripheral blood leukocytes, bone marrow, fetal liver, heart, brain, placenta, skeletal muscle, kidney, and pancreas. The anti-human alpha 4 antibody detected a 45-kDa protein in human lymphoid cell lines. Moreover, human alpha 4 (IGBP1) gene is located at q13.1-q13.3 on chromosome X.

Interleukin-4 (IL-4) induces phosphatidylinositol 3-kinase (p85) dephosphorylation. Implications for the role of SHP-1 in the IL-4-induced signals in human B cells

Interleukin 4 (IL-4) is a potent cytokine produced by T cells and to a lesser extent by tumor-associated natural killer cells, basophils, and mast cells. IL-4 treatment of T cells and macrophages leads to augmentation of their cytotoxic activity. In human B cells, IL-4 is a potent stimulator of Ig class switching from IgM to IgE. The diverse biological responses induced by IL-4 are mediated through a high affinity receptor complex (IL-4R). Although a wealth of information has accumulated regarding IL-4R, the exact mechanisms of IL-4R-mediated signaling pathways in human B cells are not well defined. In an attempt to characterize the IL-4-induced signals in human B cells, we have found that IL-4 treatment induced rapid dephosphorylation of the 85-kDa regulatory subunit of phosphatidylinositol 3-kinase. To identify the protein-tyrosine phosphatase involved in the IL-4-mediated dephosphorylation, we performed Western blot analysis using monoclonal antibodies specific to protein-tyrosine phosphatases. Upon IL-4 treatment, SHP-1 was specifically translocated to the cellular membrane fraction. Furthermore, immunoprecipitation studies revealed that SHP-1 could be specifically coimmunoprecipitated with the IL-4R as well as with phosphatidylinositol 3-kinase (p85). Collectively, our observations suggest that in addition to protein phosphorylation, protein tyrosine dephosphorylation may play a role in the IL-4-induced signaling pathways.

Implications for the assay and biological activity of interleukin-4. Results of a WHO international collaborative study

Five ampouled preparations of interleukin-4 (IL-4) have been evaluated by 36 laboratories in 14 countries for their suitability to serve as an international standard for this material in a joint international collaborative study for interleukin-3 (IL-3) and IL-4. The preparations were assayed in a wide range of in vitro bioassays and immunoassays. It is clear from the study that different recombinant preparations of IL-4 can have very different biological specific activities, including those from the same source (i.e., E. coli). In addition, immunoassay estimates of IL-4 levels did not correlate with those of bioassays, illustrating the fact that immunoassays do not necessarily measure biologically active cytokine. It is of interest that the estimates provided by the different bioassays were less variable than those produced by the immunoassays, suggesting that bioassays can be as accurate, if not more so, than immunoassays. The large reduction in the variability of estimates with the inclusion of a single reference preparation clearly illustrates the need for a single standard to assay IL-4. On the basis of the results reported here, with the agreement of the participants of the study and with the authorisation of the Expert Committee on Biological Standardization (ECBS) of the World Health Organization (WHO) the preparation of IL-4 (88/656) was established as the international standard for interleukin-4 with an assigned unitage of 1000 IU/ampoule.

An antiproliferative bioassay for interleukin-4

Interleukin-4 (IL-4) is currently being used for therapeutic intervention in a wide range of malignant diseases as an antitumour agent. Although bioassays have been developed that measure the proliferative capacity of IL-4, none measure the antiproliferative activity of this molecule. We have developed a simple, sensitive bioassay for human IL-4 based on the ability of this cytokine to inhibit the proliferation of the human lung carcinoma line, CCL-185, an easy to maintain, cytokine independent, cell line. It is rapid, reproducible and sensitive, able to detect 2 pg/ml IL-4. The assay is completely unresponsive to all other interleukins from IL-2 to IL-12, to the colony stimulating factors and transforming growth factor beta and is 100-fold less sensitive to interferon-alpha, tumour necrosis factor-alpha, IL-1 beta and IL-13. The assay can be made completely specific for IL-4 by including specific neutralizing antibodies for IL-4 and is suitable for the estimation of IL-4 in both plasma and serum samples.

T-cell lymphokines, interleukin-4 and gamma interferon, modulate the induction of vascular smooth muscle cell tissue plasminogen activator and migration by serum and platelet-derived growth factor

Platelet-derived growth factor (PDGF)-induced smooth muscle cell (SMC) fibrinolysis is necessary for SMC migration. In order to determine whether the T-cell lymphokines interleukin-4 (IL-4) and gamma interferon (gamma-IFN) affect SMC fibrinolysis and migration, we examined the effects of human recombinant IL-4 and gamma-IFN on human aortic SMC tissue-type plasminogen activator (TPA), urokinase-type plasminogen activator (UPA), and plasminogen activator inhibitor type-1 (PAI-1) antigen production, as determined by enzyme-linked immunosorbent assays. Although IL-4 had no direct effect on SMC TPA antigen, IL-4 potentiated SMC TPA antigen levels and activity in conditioned media and cellular lysates in media containing 2% fetal bovine serum but did not change UPA or PAI-1 production. gamma-IFN attenuated IL-4 augmentation of SMC TPA antigen production in conditioned media, although gamma-IFN itself had no direct effects on SMC TPA and PAI-1 antigen production. IL-4 augmented PDGF induction of SMC TPA antigen. gamma-IFN inhibited PDGF induction of SMC TPA antigen and IL-4 potentiation of this process. gamma-IFN diminished the promigratory effects of both IL-4 and PDGF on in vitro SMC migration. Tranexamic acid, a plasmin inhibitor, abrogated the stimulation of SMC migration by IL-4. Therefore, IL-4 and gamma-IFN modulate the induction of SMC TPA and SMC migration by 2% fetal bovine serum and PDGF.

Quantitative cell line based bioassays for human cytokines

Research in cytokine biology is ever increasing and it is clear that cytokines are involved in a wide range of pathological and physiological processes. The validity of such research relies heavily on the appropriate measurement of levels of cytokines in various biological samples. Amongst the currently available methods for measuring cytokine levels, it is only the biological assay of samples that can directly provide estimates of biologically active cytokines present in test samples. Of the several bioassay systems available for detecting cytokines, cell line based bioassays are the easiest to perform and provide the most precise and accurate data. The suitability of any cell line for bioassaying a particular cytokine depends on several criteria such as sensitivity, ease of growth maintenance, and cytokine specificity. The design and analysis of cell line bioassays is also important in providing valid estimates of cytokine levels. We review the most useful cell lines currently available for bioassaying cytokines and discuss the design advantages and limitations of cytokine bioassays.

Cytokine secretion induced by superantigens in peripheral blood mononuclear cells, lamina propria lymphocytes, and intraepithelial lymphocytes

Superantigens are potent inducers of T-cell proliferation and induce a broad range of cytokines, including tumor necrosis factor (TNF), gamma interferon, and interleukin 2 (IL-2). In the present study, we compared the abilities of different staphylococcal superantigens (staphylococcal enterotoxin B [SEB], staphylococcal enterotoxin E [SEE], and toxic shock syndrome toxin 1 [TSST-1]) to stimulate distinct cytokine profiles in peripheral blood mononuclear cells (PBMC), lamina propria lymphocytes (LPL), and intraepithelial lymphocytes (IEL). One million PBMC, LPL, and IEL were stimulated with various concentrations of superantigen (10 to 0.001 ng/ml) for 24, 48, and 72 h. Maximum cytokine production by PBMC, LPL, and IEL was observed for all three superantigens at 48 h at a concentration of 1 ng/ml. In PBMC, SEE and TSST-1 stimulated more IL-2 and gamma interferon than SEB. SEE and TSST-1 also stimulated more TNF and IL-4 production than SEB. In contrast, SEB stimulated more IL-6 than either SEE or TSST-1. In LPL, there was no SEE-induced IL-2 or IL-4 production, but IL-6, TNF, and gamma interferon were induced. SEB similarly induced no IL-2 or gamma interferon from the LPL, but IL-4, IL-6, and TNF were detected. TSST-1 stimulation of LPL resulted in IL-2 and TNF production but no IL-4, IL-6, or gamma interferon. In IEL, SEE induced no IL-2, IL-4, or gamma interferon but produced IL-6 and TNF, while SEB stimulation resulted in no IL-2 or gamma interferon but did result in detectable IL-4, IL-6, and TNF. Taken together, these data indicate that there are significant differences in the cytokine profiles induced by superantigens in LPL and IEL compared with those in PBMC, and these differences may relate to differences in activation requirements.

Efficient transduction of early passage human melanoma to secrete IL-4

Augmentation of tumor immunogenicity has been increasingly studied as a strategy to develop host immunity against established malignancies. Genetic modification of tumors to secrete immunoregulatory peptides such as IL-4 has been demonstrated to augment tumor immunogenicity and enhance the induction of tumor reactive lymphoid cells in animal models. To explore the ability of IL-4 to augment the immunogenicity of melanoma cells, we constructed a recombinant retrovirus vector encoding for human IL-4 and used it to transduce human melanomas. After optimizing retrovirus transduction conditions using a reporter virus, an IL-4 encoding retrovirus vector was used to transduce early and late passage melanoma cells. IL-4 production rates of up to 2000 pg/ml per 24 h per 10(6) cells were achieved, and provirus could be detected by Southern blot of the transduced cells at 0.1 copies per cell. The IL-4 produced by the melanoma cells was biologically active. Irradiated transduced melanoma cells continued to produce IL-4 for at least two weeks of observation. Thus melanoma cells can be efficiently modified to secrete biologically active IL-4, and may be suitable substrates for autologous tumor cell vaccines.

Involvement of CRAF1, a relative of TRAF, in CD40 signaling

CD40 is a receptor on the surface of B lymphocytes, the activation of which leads to B cell survival, growth, and differentiation. A yeast two-hybrid screen identified a gene, CRAF1, encoding a protein that interacts directly with the CD40 cytoplasmic tail through a region of similarity to the tumor necrosis factor-alpha (TNF-alpha) receptor-associated factors. Overexpression of a truncated CRAF1 gene inhibited CD40-mediated up-regulation of CD23. A region of CRAF1 was similar to the TNF-alpha receptor-associated factors TRAF1 and TRAF2 and so defined a shared TRAF-C domain that was necessary and sufficient for CD40 binding and homodimerization. The CRAF1 sequence also predicted a long amphipathic helix, a pattern of five zinc fingers, and a zinc ring finger. It is likely that other members of the TNF receptor superfamily use CRAF-related proteins in their signal transduction processes.

Cytokines and growth factors signal through tyrosine phosphorylation of a family of related transcription factors

The ability of cytokines to activate distinct but overlapping sets of genes defines their characteristic biological response. We now show that IFN gamma, IL-3, IL-4, IL-6, erythropoietin, EGF, and CSF-1 activate differing members of a family of latent cytoplasmic transcription factors. Although these factors have distinct physical and functional properties and exhibit different patterns of expression, they share many important features, including recognition of a related set of enhancer elements, rapid activation, tyrosine phosphorylation, and cross-reactivity to antibodies against p91, a cytoplasmic signaling protein activated by IFN alpha, IFN gamma, and IL-6. These shared features point to either parallel or common patterns of signal transduction. A general model of cytokine signal transduction is presented, in which receptor-associated tyrosine kinases activate ligand-specific members of a family of signal-transducing factors. Once activated, these factors carry their signals to the nucleus, where they bind a family of related enhancer elements.

Expression of high-affinity IL-4 receptors on human melanoma, ovarian and breast carcinoma cells

It has previously been shown that murine sarcoma cells express high-affinity IL-4 receptors (IL-4R) which are internalized after binding to the ligand (Puri et al., Cancer Res 1991; 51:3011-7). We have also reported that human renal cell carcinoma cells express high-affinity IL-4R, and IL-4 inhibits tumour growth in vitro (Obiri et al., J Clin Invest 1993; 91:88). In this study we investigated the expression and function of IL-4R on other human solid tumours. Human melanoma, ovarian carcinoma and breast carcinoma cell lines were assessed for the cell surface expression of IL-4R by radio-ligand receptor binding and for IL-4R gene expression by Northern blot analysis. Primary cultures of mesothelioma and neurofibrosarcoma cells were similarly investigated. Human melanoma, ovarian carcinoma and breast carcinoma cell lines expressed IL-4R on their cell surface with a dissociation constant (Kd) of 140-549 pM. These tumour lines expressed a single 4 kb species of mRNA for IL-4R. Similarly, primary cultures of mesothelioma and neurofibrosarcoma cells were positive for the IL-4R mRNA by Northern blot analysis. Fresh, non-cultured mesothelioma and neurofibrosarcoma tumour sections were also positive for the presence of IL-4R as determined by immunohistochemistry of frozen sections using anti-IL-4R antibody. In order to study possible functions of IL-4R, we evaluated the effects of IL-4 on cell growth and its effect on MHC antigen expression in the presence or absence of interferon-gamma (IFN-gamma). In tissue culture, IL-4 reduced the growth of tumour cell lines and primary cell cultures studied. IL-4 had very little effect on MHC class I antigen expression on ovarian, breast and melanoma cell lines; however, MHC class II (HLA-DR) expression was enhanced on melanoma and breast carcinoma cells. IL-4 also enhanced the IFN-gamma-induced class II expression on melanoma and breast carcinoma cells. Taken together, our observations indicate that IL-4R are expressed on a variety of human solid tumours and these receptors may be functional. IL-4 alone and in combination with IFN-gamma may play a role in host immune response against cancers.

Measurement and computation of murine interleukin-4 and interferon-gamma by exploiting the unique abilities of these lymphokines to induce the secretion of IgG1 and IgG2a

A specific and new method for measuring Interleukin-4 and Interferon-gamma, based on the estimation of IgG1 and IgG2a isotypes secretion from B cells is described. An antagonizing effect of Interferon-gamma in the production of IgG1 induced by Interleukin-4 was neutralized by using antibody to Interferon-gamma. Similarly, the interference of Interleukin-4 in the Interferon-gamma mediated enhancement of IgG2a production was blocked by anti-Interleukin-4 antibody. The high concentrations of Interleukin-4 and Interferon gamma inhibited the secretion of IgG1 and IgG2a respectively. Therefore, in the assay described, the samples containing the cytokines were so diluted that their activity fell into the non-inhibitory zone. A computer program has also been developed for determining the concentrations of lymphokines.

Detection and measurement of cytokines

Accurate and sensitive methods for the measurement and detection of cytokines are an obvious pre-requisite for the study of cytokine biology, biochemistry and the possible involvement of these molecules in pathology. In this review, the various methods available for cytokine measurement and detection (bioassays, immunoassays and other procedures) are described and compared. A critical appraisal of the potential advantages and limitations of the techniques is included.

Assays for lymphokines, cytokines and their receptors

There have been several recent developments in the detection of cytokines, their receptors, and the genes that encode them. New methods for characterizing cytokines and lymphokines include the use of molecular hybridization techniques, bioassays and antibody-mediated detection systems. The most common techniques used for identifying and characterizing cytokine receptors rely upon the use of radiolabeled, fluoresceinated or biotinylated ligands.