The IL23 axis plays a key role in the pathogenesis of IBD

Exciting new results from a genetic study in humans and functional studies in mice have pinpointed interleukin 23 (IL23) and its receptor as a key pathway in the pathogenesis of inflammatory bowel disease (IBD). These findings reveal a hitherto unappreciated role for the IL23 axis in intestinal inflammation and may open new avenues for development of therapeutic strategies in IBD.

Human TH17 lymphocytes promote blood-brain barrier disruption and central nervous system inflammation

T(H)17 lymphocytes appear to be essential in the pathogenesis of numerous inflammatory diseases. We demonstrate here the expression of IL-17 and IL-22 receptors on blood-brain barrier endothelial cells (BBB-ECs) in multiple sclerosis lesions, and show that IL-17 and IL-22 disrupt BBB tight junctions in vitro and in vivo. Furthermore, T(H)17 lymphocytes transmigrate efficiently across BBB-ECs, highly express granzyme B, kill human neurons and promote central nervous system inflammation through CD4+ lymphocyte recruitment.

Investigation of the IL23R gene in a Spanish rheumatoid arthritis cohort

Recently, a genome-wide association study identified the interleukin-23 receptor gene (IL23R) as an inflammatory bowel disease (IBD) associated gene. Given the involvement of IL23R in T-cell regulation, we decided to test whether this gene is associated with rheumatoid arthritis (RA). Eight IL23R gene polymorphisms (rs1,004,819, rs7,517,847, rs10,489,629, rs11,209,026, rs1,343,151, rs10,889,677, rs11,209,032, and rs1,495,965) were selected among the 10 most associated SNPs from the IBD study. A total of 322 RA patients and 342 healthy controls were genotyped for the selected SNPs using a Taqman 5' allelic discrimination assay. We did not find statistically significant differences when we compared allele and genotype frequencies between RA patients and controls for none of the IL23R gene polymorphisms under study. We did not observe significant differences when RA patients were stratified according to their clinical and demographic features. We conclude that the IL23R gene does not seem to be associated with RA predisposition in a Spanish population.

Vesicular stomatitis virus glycoprotein G activates a specific antiviral Toll-like receptor 4-dependent pathway

We have previously shown that mutations of CD14 or TLR4 impair type I interferon (IFN) production and macrophage survival during infection with vesicular stomatitis virus (VSV). We now report that VSV glycoprotein G (gpG) is essential for the induction of a previously unrecognized CD14/TLR4-dependent response pathway in which the adapter TRAM has predominant importance, absent any need for MyD88 or Mal, and with only a partial requirement for TRIF. Downstream of TRAM, IRF7 activation leads to a type I IFN response. The pathway is utilized by myeloid dendritic cells (mDCs) and macrophages rather than plasmacytoid DCs. This new mode of TLR4 signal transduction, which does not stimulate NF-kappaB activation, reveals the importance of viral protein recognition by mDCs and shows that TLR4 can drive qualitatively different events within the cell in response to different ligands.

Salmonella-induced SipB-independent cell death requires Toll-like receptor-4 signalling via the adapter proteins Tram and Trif

Salmonella enterica serovar typhimurium (S. typhimurium) is an intracellular pathogen that causes macrophage cell death by at least two different mechanisms. Rapid cell death is dependent on the Salmonella pathogenicity island-1 protein SipB whereas delayed cell death is independent of SipB and occurs 18-24 hr post infection. Lipopolysaccharide (LPS) is essential for the delayed cell death. LPS is the main structural component of the outer membrane of Gram-negative bacteria and is recognized by Toll-like receptor 4, signalling via the adapter proteins Mal, MyD88, Tram and Trif. Here we show that S. typhimurium induces SipB-independent cell death through Toll-like receptor 4 signalling via the adapter proteins Tram and Trif. In contrast to wild type bone marrow derived macrophages (BMDM), Tram(-/-) and Trif(-/-) BMDM proliferate in response to Salmonella infection.

Selective use of TRAM in lipopolysaccharide (LPS) and lipoteichoic acid (LTA) induced NF-kappaB activation and cytokine production in primary human cells: TRAM is an adaptor for LPS and LTA signaling

TLR signal via Toll-IL-1R (TIR) homology domain-containing adaptor proteins. One of these adaptors, Toll-IL-1R domain-containing adaptor inducing IFN-beta-related adaptor molecule (TRAM), has been shown to be essential for TLR4 signaling in TRAM(-/-) mice and cell lines. Previously, we showed that MyD88 or Mal dominant-negative constructs did not inhibit LPS induction of cytokines in primary human M-CSF-derived macrophages. A possible explanation was redundancy of the adaptors during LPS signaling. TRAM is a suitable candidate to compensate for these adaptors. To investigate a potential role for TRAM in LPS signaling in human M-CSF-derived macrophages, we engineered an adenoviral construct expressing dominant-negative TRAM-C117H (AdTRAMdn). Synovial fibroblasts (SF) and human umbilical endothelial cells (HUVECs) were used as a nonmyeloid comparison. AdTRAMdn inhibited LPS-induced signaling in SFs and HUVECs, reducing NF-kappaB activation and cytokine production, but did not inhibit LPS signaling in M-CSF-derived human macrophages. Further investigation of other TLR ligands showed that AdTRAMdn was also able to inhibit signaling initiated by lipoteichoic acid, a TLR2 ligand, in SFs and HUVECs and lipoteichoic acid and macrophage-activating lipopeptide 2 signaling was also inhibited in TRAM(-/-) murine embryonic fibroblasts. We conclude that TRAM is an adaptor protein for both TLR4 and TLR2/6 signaling in SFs, HUVECs, and murine embryonic fibroblasts, but cannot demonstrate a role in human macrophages.

Human interleukin 24 (MDA-7/IL-24) protein kills breast cancer cells via the IL-20 receptor and is antagonized by IL-10

The melanoma differentiation-associated gene-7 (mda-7/IL-24) is a unique member of the interleukin 10 (IL-10) family of cytokines, with ubiquitous tumor cell pro-apoptotic activity. Recent data have shown that IL-24 is secreted as a glycosylated protein and functions as a pro-Th1 cytokine and as a potent anti-angiogenic molecule. In this study, we analyzed the activity of Ad-mda7 and its protein product, secreted IL-24, against human breast cancer cells. We show that Ad-mda7 transduction of human breast cancer cells results in G(2)/M phase cell cycle arrest and apoptotic cell death, which correlates with secretion of IL-24 protein. Neutralizing antibody against IL-24 significantly inhibited Ad-mda7 cytotoxicity. IL-24 and IL-10 both engage their cognate receptors on breast cancer cells resulting in phosphorylation and activation of STAT3, however, IL-10 receptor binding failed to induce cell killing, indicating that tumor cell killing by IL-24 is independent of STAT3 phosphorylation. Treatment with exogenous IL-24 induced apoptosis in breast cancer cells and this effect was abolished by addition of anti-IL-24 antibody or anti-IL-20R1, indicating that bystander cell killing is mediated via IL-24 binding to the IL-20R1/IL-20R2 heterodimeric receptor complex. Co-administration of the related cytokine IL-10 inhibited killing mediated by IL-24 and concomitantly inhibited IL-24 mediated up-regulation of the tumor suppressor proteins, p53 and p27(Kip1). In summary, we have defined a tumor-selective cytotoxic bystander role for secreted IL-24 protein and identified a novel receptor-mediated death pathway in breast cancer cells, wherein the related cytokines IL-24 and IL-10 exhibit antagonistic activity.

Interleukin (IL)-19, IL-20 and IL-24 are produced by and act on keratinocytes and are distinct from classical ILs

Due to their structural similarity, interleukin (IL)-19, IL-20, IL-22, IL-24 and IL-26 were combined with IL-10 in the so-called IL-10 family. To expand the knowledge on IL-19, IL-20 and IL-24, we systematically and quantitatively analysed the expression of these mediators and their receptor chains in vitro and in vivo under various conditions and in comparison with other IL-10 family members. In vitro, IL-19, IL-20 and IL-24 were produced not only by activated immune cells, particularly monocytes, but also to a similar extent by keratinocytes. IL-1beta increased the expression of these mediators 1000-fold (IL-19) and 10-fold (IL-20 and IL-24) in keratinocytes. In vivo, these cytokines were expressed preferentially in inflamed tissues. The absence of either R1 chain for the two types of receptor complexes for these cytokines (IL-20R1/IL-20R2 and IL-22R1/IL-20R2) on immune cells implies that they cannot act on these cells. In fact, IL-19, IL-20 and IL-24 did not induce activation of signal transducer and activator of transcription (STAT) molecules in immune cells. Instead, several tissues, particularly the skin, tissues from the reproductive and respiratory systems, and various glands appeared to be the main targets of these mediators. Keratinocytes expressed both receptor complexes; however, the expression of IL-22R1 was 10 times higher than that of IL-20R1. Interferon-gamma further increased the expression of IL-22R1 and decreased that of IL-20R1, suggesting that under T1 cytokine conditions these mediators primarily affect keratinocytes via the IL-22R1/IL-20R2 complex. In summary, these data support the notion that IL-19, IL-20 and IL-24 are distinct from classical ILs and constitute a separate subfamily of mediators within the IL-10 family.

Innate Immune Responses to EndosymbioticWolbachiaBacteria inBrugia malayiandOnchocerca volvulusAre Dependent on TLR2, TLR6, MyD88, and Mal, but Not TLR4, TRIF, or TRAM

The discovery that endosymbiotic Wolbachia bacteria play an important role in the pathophysiology of diseases caused by filarial nematodes, including lymphatic filariasis and onchocerciasis (river blindness) has transformed our approach to these disabling diseases. Because these parasites infect hundreds of millions of individuals worldwide, understanding host factors involved in the pathogenesis of filarial-induced diseases is paramount. However, the role of early innate responses to filarial and Wolbachia ligands in the development of filarial diseases has not been fully elucidated. To determine the role of TLRs, we used cell lines transfected with human TLRs and macrophages from TLR and adaptor molecule-deficient mice and evaluated macrophage recruitment in vivo. Extracts of Brugia malayi and Onchocerca volvulus, which contain Wolbachia, directly stimulated human embryonic kidney cells expressing TLR2, but not TLR3 or TLR4. Wolbachia containing filarial extracts stimulated cytokine production in macrophages from C57BL/6 and TLR4(-/-) mice, but not from TLR2(-/-) or TLR6(-/-) mice. Similarly, macrophages from mice deficient in adaptor molecules Toll/IL-1R domain-containing adaptor-inducing IFN-beta and Toll/IL-1R domain-containing adaptor-inducing IFN-beta-related adaptor molecule produced equivalent cytokines as wild-type cells, whereas responses were absent in macrophages from MyD88(-/-) and Toll/IL-1R domain-containing adaptor protein (TIRAP)/MyD88 adaptor-like (Mal) deficient mice. Isolated Wolbachia bacteria demonstrated similar TLR and adaptor molecule requirements. In vivo, macrophage migration to the cornea in response to filarial extracts containing Wolbachia was dependent on TLR2 but not TLR4. These results establish that the innate inflammatory pathways activated by endosymbiotic Wolbachia in B. malayi and O. volvulus filaria are dependent on TLR2-TLR6 interactions and are mediated by adaptor molecules MyD88 and TIRAP/Mal.

An essential role for IL-17 in preventing pathogen-initiated bone destruction: recruitment of neutrophils to inflamed bone requires IL-17 receptor-dependent signals

IL-17 and its receptor are founding members of a novel family of inflammatory cytokines. IL-17 plays a pathogenic role in rheumatoid arthritis (RA)-associated bone destruction. However, IL-17 is also an important regulator of host defense through granulopoiesis and neutrophil trafficking. Therefore, the role of IL-17 in pathogen-initiated bone loss was not obvious. The most common form of infection-induced bone destruction occurs in periodontal disease (PD). In addition to causing significant morbidity, PD is a risk factor for atherosclerotic heart disease and chronic obstructive pulmonary disease (COPD). Similar to RA, bone destruction in PD is caused by the immune response. However, neutrophils provide critical antimicrobial defense against periodontal organisms. Since IL-17 is bone destructive in RA but a key regulator of neutrophils, we examined its role in inflammatory bone loss induced by the oral pathogen Porphyromonas gingivalis in IL-17RA-deficient mice. These mice showed enhanced periodontal bone destruction, suggesting a bone-protective role for IL-17, reminiscent of a neutrophil deficiency. Although IL-17RA-deficient neutrophils functioned normally ex vivo, IL-17RA knock-out (IL-17RA(KO)) mice exhibited reduced serum chemokine levels and concomitantly reduced neutrophil migration to bone. Consistently, CXCR2(KO) mice were highly susceptible to alveolar bone loss; interestingly, these mice also suggested a role for chemokines in maintaining normal bone homeostasis. These results indicate a nonredundant role for IL-17 in mediating host defense via neutrophil mobilization.

Age dependent increase in early resistance of mice to Mycobacterium tuberculosis is associated with an increase in CD8 T cells that are capable of antigen independent IFN-gamma production

The lungs of naïve 18-month-old mice contain an abundant resident population of CD8 T cells that express typical markers of memory, express elevated levels of Th1 cytokine receptors on their surface, and are capable of non-specific IFN-gamma production in response to a Th1 cytokine cocktail. In this study we characterize this population of CD8 T cells in the lungs and spleens of mice with increasing age. In general, the proportion of CD8 T cells expressing markers of memory and Th1 cytokine receptors increased with age. The enhanced ability of CD8 T cells to produce IFN-gamma in an antigen independent manner followed this pattern as well, beginning to increase between 6 and 12 months of age. Interestingly, the phenotypic and functional age-related changes in CD8 T cells were also associated with a progressive age-related increase in early resistance to Mycobacterium tuberculosis. Taken together, these data suggest that as mice age a population of memory CD8 T cells, that are capable of contributing to innate immune responses to M. tuberculosis, gradually emerges and could be relevant for developing strategies to enhance immunity in the elderly.

Overcoming original antigenic sin to generate new CD8 T cell IFN-gamma responses in an antigen-experienced host

The failure to mount effective immunity to virus variants in a previously virus-infected host is known as original antigenic sin. We have previously shown that prior immunity to a virus capsid protein inhibits induction by immunization of an IFN-gamma CD8+ T cell response to an epitope linked to the capsid protein. We now demonstrate that capsid protein-primed CD4+ T cells secrete IL-10 in response to capsid protein presented by dendritic cells, and deviate CD8+ T cells responding to a linked MHC class I-restricted epitope to reduce IFN-gamma production. Neutralizing IL-10 while delivering further linked epitope, either in vitro or in vivo, restores induction by immunization of an Ag-specific IFN-gamma response to the epitope. This finding demonstrates a strategy for overcoming inhibition of MHC class I epitopes upon immunization of a host already primed to Ag, which may facilitate immunotherapy for chronic viral infection or cancer.

IL-17A-producing neutrophil-regulatory Tn lymphocytes

The proinflammatory cytokine IL-17A, mainly produced by specialized T cells, plays an important homeostatic role in regulating neutrophil production and blood neutrophil counts. This review will assemble and discuss the evidence for this function of IL-17A-producing cells, which are collectively called neutrophil-regulatory T cells or Tn cells. IL-17A-producing lymphocytes are most abundant in the mesenteric lymph node, where they account for 0.15% of all lymphocytes. About 60% of the Tn cells are gammadelta T cells, about 25% NKTlike cells, and less than 15% are CD4 T cells. These latter cells are also known as T-17 or ThIL-17 cells, a subset of Tn cells that also plays an important role in autoimmune diseases. IL-17A produced by Tn cells regulates the production of G-CSF, which in turn promotes the proliferation of promyelocytes and maturation of neutrophils. This homeostatic mechanism plays an important role in normal physiology and in host defense against bacterial infections. This review is aimed at highlighting the important role of IL-17A-producing T cells at the interface between the adaptive and innate immune system.

Regulation of adrenal glucocorticoid synthesis by interleukin-10: a preponderance of IL-10 receptor in the adrenal zona fasciculata

Several lines of evidence indicate that cytokines can affect adrenal function. To date most of these cytokines have been shown to be pro-inflammatory, such as interleukin (IL)-1, tumor necrosis factor (TNFalpha), and IL-6. However, we have previously shown that IL-10-/- (IL-10 knockout) mice have higher serum corticosterone levels than IL-10+/+ (wild type) mice following acute immune and physiologic stress, implying that IL-10, an anti-inflammatory cytokine, regulates glucocorticoid synthesis in a negative manner. Here, we show that IL-10 knockout mice produce more corticosterone under basal conditions as well (shown by ELISA). We further support this contention by showing that in Y-1 adrenocortical cells IL-10 inhibits steroid production (StAR) (measured by the production of the corticosterone precursor, progesterone), the expression of steroidogenic acute regulatory protein (semi-quantitative RT-PCR), as well as the activity of the proximal steroidogenic enzymes P450scc and/or 3beta-hydroxysteroid dehydrogenase (3beta-HSD) (measured by progesterone production in 22(R)-hydroxycholesterol-treated cells). Interestingly, all of the above-mentioned effects of IL-10 occur through its inhibition of ACTH effects, but not by IL-10 alone. Furthermore, immunocytochemistry data shows that the region of the adrenal gland responsible for the vast majority of corticosterone synthesis, the zona fasciculata, predominantly expresses the IL-10 receptor 1 (IL-10R1), with little expression in the zona glomerulosa and reticularis. These data demonstrate that IL-10 could play an important role in the regulation of glucocorticoid biosynthesis and in maintenance of homeostasis and immunity during periods of stress.

Protection from lethal septic peritonitis by neutralizing the biological function of interleukin 27

The immune response to bacterial infections must be tightly controlled to guarantee pathogen elimination while preventing tissue damage by uncontrolled inflammation. Here, we demonstrate a key role of interleukin (IL)-27 in regulating this critical balance. IL-27 was rapidly induced during murine experimental peritonitis induced by cecal ligation and puncture (CLP). Furthermore, mice deficient for the EBI3 subunit of IL-27 were resistant to CLP-induced septic peritonitis as compared with wild-type controls, and this effect could be suppressed by injection of recombinant single-chain IL-27. EBI3^−/− mice displayed significantly enhanced neutrophil migration and oxidative burst capacity during CLP, resulting in enhanced bacterial clearance and local control of infection. Subsequent studies demonstrated that IL-27 directly suppresses endotoxin-induced production of reactive oxygen intermediates by isolated primary granulocytes and macrophages. Finally, in vivo blockade of IL-27 function using a newly designed soluble IL-27 receptor fusion protein led to significantly increased survival after CLP as compared with control-treated mice. Collectively, these data identify IL-27 as a key negative regulator of innate immune cell function in septic peritonitis. Furthermore, in vivo blockade of IL-27 is a novel potential therapeutic target for treatment of sepsis.

Identification of interleukin-13 receptor alpha2 peptide analogues capable of inducing improved antiglioma CTL responses

Restricted and high-level expression of interleukin-13 receptor alpha2 (IL-13Ralpha2) in a majority of human malignant gliomas makes this protein an attractive vaccine target. We have previously described the identification of the IL-13Ralpha2(345-353) peptide as a human leukocyte antigen-A2 (HLA-A2)-restricted CTL epitope. However, as it remains unclear how efficiently peptide-based vaccines can induce specific CTLs in patients with malignant gliomas, we have examined whether analogue epitopes could elicit heteroclitic antitumor T-cell responses versus wild-type peptides. We have created three IL-13Ralpha2 analogue peptides by substitutions of the COOH-terminal isoleucine (I) for valine (V) and the NH(2)-terminal tryptophan (W) for either alanine (A), glutamic acid (E), or nonsubstituted (W; designated as 1A9V, 1E9V, and 9V, respectively). In comparison with the native IL-13Ralpha2 epitope, the analogue peptides 9V and 1A9V displayed higher levels of binding affinity and stability in HLA-A2 complexes and yielded an improved stimulatory index for patient-derived, specific CTLs against the native epitope expressed by HLA-A2(+) glioma cells. In HLA-A2-transgenic HHD mice, immunization with the peptides 9V and 1A9V induced enhanced levels of CTL reactivity and protective immunity against an intracranial challenge with IL13Ralpha2-expressing syngeneic tumors when compared with vaccines containing the native IL-13Ralpha2 epitope. These findings indicate highly immunogenic IL-13Ralpha2 peptide analogues may be useful for the development of vaccines capable of effectively expanding IL-13Ralpha2-specific, tumor-reactive CTLs in glioma patients.

The IL-21 receptor augments Th2 effector function and alternative macrophage activation

The IL-21 receptor (IL-21R) shows significant homology with the IL-4R, and CD4+ Th2 cells are an important source of IL-21. Here we examined whether the IL-21R regulates the development of Th2 responses in vivo. To do this, we infected IL-21R-/- mice with the Th2-inducing pathogens Schistosoma mansoni and Nippostrongylus brasiliensis and examined the influence of IL-21R deficiency on the development of Th2-dependent pathology. We showed that granulomatous inflammation and liver fibrosis were significantly reduced in S. mansoni-infected IL-21R-/- mice and in IL-21R+/+ mice treated with soluble IL-21R-Fc (sIL-21R-Fc). The impaired granulomatous response was also associated with a marked reduction in Th2 cytokine expression and function, as evidenced by the attenuated IL-4, IL-13, AMCase, Ym1, and FIZZ1 (also referred to as RELMalpha) responses in the tissues. A similarly impaired Th2 response was observed following N. brasiliensis infection. In vitro, IL-21 significantly augmented IL-4Ralpha and IL-13Ralpha1 expression in macrophages, resulting in increased FIZZ1 mRNA and arginase-1 activity following stimulation with IL-4 and IL-13. As such, these data identify the IL-21R as an important amplifier of alternative macrophage activation. Collectively, these results illustrate an essential function for the IL-21R in the development of pathogen-induced Th2 responses, which may have relevance in therapies for both inflammatory and chronic fibrotic diseases.

Characterization of a novel human tumor antigen interleukin-13 receptor alpha2 chain

The interleukin (IL)-13 receptor alpha2 (IL-13Ralpha2) chain is a primary binding and internalization subunit for a Th2-derived immune regulatory cytokine, IL-13. Although extremely high levels of IL-13Ralpha2 chain are expressed on a variety of human tumor cells and specimens, its precise role in tumor immunology has not been defined. To investigate the role of IL-13Ralpha2 in tumor immunity, we used D5 melanoma cells stably transfected with the human IL-13Ralpha2 gene (D5alpha2) to assess the effect of an IL-13Ralpha2 DNA vaccine in immunocompetent animals. Prophylactic immunization of mice with the IL-13Ralpha2 DNA vaccine resulted in protection against D5alpha2 tumor development. In vivo depletion experiments in C57BL/6 and RAG-2 knockout mice indicated that both T and B cells, but not natural killer cells, were required for the tumor protection. In addition, antibody induced by the IL-13Ralpha2 DNA vaccine showed a modest but significant inhibitory effect on D5alpha2 cells in vitro, suggesting that the antibody is biologically functional. The IL-13Ralpha2 DNA vaccine also exhibited antitumor activity against established D5alpha2 tumors in mice. Histologic analysis of regressing tumors identified infiltration of CD4+ and CD8+ T cells and the expression of CXCL9 chemokine in tumors. Taken together, our results identify the human IL-13Ralpha2 chain as a novel tumor rejection antigen.

Methylation of the IL-12Rbeta2 gene as novel tumor escape mechanism for pediatric B-acute lymphoblastic leukemia cells

Previous studies have shown that the interleukin-12 receptor beta2 (IL-12Rbeta2) gene is expressed in normal naive, germinal center and memory B cells but not in their malignant counterparts. The aim of this study was to investigate (i) whether the IL-12Rbeta2 gene is silenced in B-cell acute lymphoblastic leukemia (B-ALL) cells, and (ii) what the functional implications of such silencing for tumor growth are. Here, we show that although mature B cells expressed both chains of the IL-12R, normal pro-B and pre-B cells failed to express the IL-12Rbeta2 chain. Similarly, primary tumor cells from pediatric pro-B, early pre-B, and pre-B ALL (30 cases) did not express the IL-12Rbeta2 chain. IL-12Rbeta2 gene silencing in B-ALL was found to depend on methylation of a CpG island in exon 1. Such methylation was not detected in normal early B cells that when differentiated into mature B cells expressed the IL-12Rbeta2 gene. Detection of IL-12Rbeta2 mRNA and protein in the tumorigenic 697 pre-B-ALL cell line allowed to perform functional experiments in severe combined immunodeficient/nonobese diabetic mice receiving 697 cells with or without human recombinant IL-12 (hrIL-12). hrIL-12 administration reduced tumor growth and metastasis through antiproliferative and proapoptotic rather than antiangiogenic, activities. In conclusion, epigenetic silencing of the IL-12Rbeta2 gene represents a novel mechanism of tumor escape for B-ALL cells.

Divergent effects of IL-12 and IL-23 on the production of IL-17 by human T cells

IL-23 is regarded as a major pro-inflammatory mediator in autoimmune disease, a role which until recently was ascribed to its related cytokine IL-12. IL-23, an IL-12p40/p19 heterodimeric protein, binds to IL-12Rbeta1/IL-23R receptor complexes. Mice deficient for p19, p40 or IL-12Rbeta1 are resistant to experimental autoimmune encephalomyelitis or collagen-induced arthritis. Paradoxically, however, IL-12Rbeta2- and IL-12p35-deficient mice show remarkable increases in disease susceptibility, suggesting divergent roles of IL-23 and IL-12 in modulating inflammatory processes. IL-23 induces IL-17, which mediates inflammation and tissue remodeling, but the role of IL-12 in this respect remains unidentified. We investigated the roles of exogenous (recombinant) and endogenous (macrophage-derived) IL-12 and IL-23, on IL-17-induction in human T-cells. IL-23 enhanced IL-17 secretion, as did IL-2, IL-15, IL-18 and IL-21. In contrast, IL-12 mediated specific inhibition of IL-17 production. These data support the role of IL-23 in inflammation through stimulating IL-17 production by T lymphocytes, and importantly indicate a novel regulatory function for IL-12 by specifically suppressing IL-17 secretion. These data therefore extend previous reports that had indicated unique functions for IL-23 and IL-12 due to distinct receptor expression and signal transduction complexes, and provide novel insights into the regulation of immunity, inflammation and immunopathology.

The IL-4 and IL-13 pseudomonas exotoxins: new hope for brain tumor therapy

✓ Targeting cell surface receptors with cytotoxins or immunotoxins provides a unique opportunity for brain tumor therapy. The authors have discovered that receptors for two cytokines, interleukin (IL)-4 and IL-13, are overexpressed on tumor biopsy samples and on cell lines derived from a variety of human tumors, including brain tumors. These investigators have demonstrated that the structure of these cytokine receptors on tumor cells is different from that found on normal immune cells. In human solid tumor cells, IL-4 binds to two chains (IL-4Rα and IL-13Rα1), whereas IL-13 binds to three chains in many solid tumor cells, including glioma cells (to IL-4Rα, IL-13Rα1, and IL-13Rα2). To target IL-4Rs and IL-13Rs, the authors generated two recombinant fusion cytotoxins composed of IL-4 or IL-13 and a mutated form of pseudomonas exotoxin (PE), which for simplicity are called IL4-PE and IL13-PE in this paper. These chimeric cytotoxins are highly toxic in vitro to human tumor cell lines and primary cell cultures, including glioma cells, and in vivo to animal models of human tumors, including gliomas. In contrast, normal cells, including immune, endothelial, and brain cells, are spared from their cytotoxic effects. Based on numerous preclinical studies, IL13-PE (also known as IL13-PE38QQR or cintredekin besudotox) has been tested in four Phase I/II clinical trials. The agent IL13-PE was administered intracranially by using convection-enhanced delivery (CED). The drug was delivered through catheters placed either directly into the tumor bed or in the peritumoral region after resection of the lesion. The CED of IL13-PE was fairly well tolerated, with a reasonable benefit/risk profile for treatment of patients with glioma. Based on Phase I/II clinical trials, the Phase III Randomized Evaluation of CED of IL13-PE Compared to Gliadel Wafer with Survival Endpoint Trial (also known as the PRECISE Trial) in patients with initial recurrence of glioblastoma multiforme has recently been completed. Patients are being monitored for safety of the agents, duration of overall survival, and quality of life.

T-bet regulates Th1 responses through essential effects on GATA-3 function rather than on IFNG gene acetylation and transcription

T helper type 1 (Th1) development is facilitated by interrelated changes in key intracellular factors, particularly signal transducer and activator of transcription (STAT)4, T-bet, and GATA-3. Here we show that CD4⁺ cells from T-bet^−/− mice are skewed toward Th2 differentiation by high endogenous GATA-3 levels but exhibit virtually normal Th1 differentiation provided that GATA-3 levels are regulated at an early stage by anti–interleukin (IL)-4 blockade of IL-4 receptor (R) signaling. In addition, under these conditions, Th1 cells from T-bet^−/− mice manifest IFNG promotor accessibility as detected by histone acetylation and deoxyribonuclease I hypersensitivity. In related studies, we show that the negative effect of GATA-3 on Th1 differentiation in T-bet^−/− cells arises from its ability to suppress STAT4 levels, because if this is prevented by a STAT4-expressing retrovirus, normal Th1 differentiation is observed. Finally, we show that retroviral T-bet expression in developing and established Th2 cells leads to down-regulation of GATA-3 levels. These findings lead to a model of T cell differentiation that holds that naive T cells tend toward Th2 differentiation through induction of GATA-3 and subsequent down-regulation of STAT4/IL-12Rβ2 chain unless GATA-3 levels or function is regulated by T-bet. Thus, the principal function of T-bet in developing Th1 cells is to negatively regulate GATA-3 rather than to positively regulate the IFNG gene.

CD8+ T cells in HIV disease exhibit cytokine receptor perturbation and poor T cell receptor activation but are responsive to gamma-chain cytokine-driven proliferation

BACKGROUND

Cytokines are important for inducing T cell maturation, proliferation, and survival. Despite the known dysregulation of cytokines in human immunodeficiency virus (HIV) infection, cytokine receptor expression is relatively unexplored.

METHODS

We examined maturation markers (naive, central memory, effector memory, and effector); the cytokine receptors interleukin (IL)-2R beta , common gamma (C gamma ) chain, IL-7R alpha , IL-15R alpha; and proliferative responses of T cells in a cohort of HIV-infected pediatric patients (median age, 14.82 years) receiving antiretroviral therapy, arbitrarily designated as immunologic responders (group I) and nonresponders (group II) on the basis of a CD4+ T cell count cutoff of 25%.

RESULTS

Patients had increased percentages of effector memory CD8+ T cells, in comparison with those in healthy control subjects, with reduced expression of IL-7R alpha in the central memory and effector memory subsets and of the C gamma chain in all maturation subsets of CD8+ T cells. IL-7R alpha +CD8+ T cell percentages were directly correlated with CD4+ T cell percentages. In immunologic nonresponders, anti-CD3+ or HIV Gag antigen-induced CD8+ T cell proliferation was impaired, but proliferation in response to the homeostatic cytokines IL-2 and IL-15 was preserved.Conclusions. Cytokine receptor deficiencies may contribute to immune deficiency in HIV-infected patients, and gamma -chain-utilizing cytokines may play an important role in vivo in maintaining the memory subsets of T cells in patients with CD4+ T cell deficiency.

IL-17E upregulates the expression of proinflammatory cytokines in lung fibroblasts

BACKGROUND

IL-17E is a new TH2 cytokine that promotes airway eosinophilia in mice. IL-17E proinflammatory activity has been proposed to involve induction of cytokine and chemokine production. Recruitment of inflammatory cells may be mediated by tissue-resident cells.

OBJECTIVE

This study aimed to evaluate whether fibroblasts represent a target of IL-17E for the production of eosinophil active mediators in the lung.

METHODS

Expression of IL-17B receptor (IL-17BR), a receptor for IL-17E, was evaluated by immunofluorescent staining, Western blot, and real-time PCR in human primary lung fibroblasts. Mediator production was analyzed by using real-time PCR and ELISA after stimulation of fibroblasts with IL-17E alone or in combination with TNF-alpha and TGF-beta1. Expression of IL-17E and of eosinophil major basic protein was evaluated by immunohistochemistry in bronchial biopsies from subjects with asthma.

RESULTS

Human primary lung fibroblasts constitutively expressed IL-17BR. IL-17BR mRNA levels were increased in cells stimulated with TNF-alpha and decreased with TGF-beta1. IL-17E slightly upregulated CC chemokine ligand (CCL)-5, CCL-11, GM-CSF, and CXC chemokine ligand (CXCL)-8 mRNA in fibroblasts. Moreover, IL-17E and TNF-alpha synergistically induced GM-CSF and CXCL-8 mRNA. IL-17E also potentiated the upregulation of CXCL-8 transcripts observed with TGF-beta1. In contrast, TGF-beta1 decreased IL-17E-induced CCL-11 mRNA. The capacity of IL-17E to enhance GM-CSF and CXCL-8 responses to TNF-alpha was accompanied by production and secretion of both proteins by lung fibroblasts. Finally, IL-17E was detected in asthma in eosinophil-infiltrated bronchial submucosa.

CONCLUSION

IL-17E may contribute to the induction and maintenance of eosinophilic inflammation in the airways by acting on lung fibroblasts. This study supports a role for IL-17E in asthma pathophysiology.

Cutting edge: the development of IL-4-producing B cells (B effector 2 cells) is controlled by IL-4, IL-4 receptor alpha, and Th2 cells

Although IL-4-producing B cells (B effector 2 cells) are found following infection and immunization, the signals regulating IL-4 production by Be2 cells are unknown. We show that culturing naive B cells with Th2 cells induces up-regulation of IL-4 in the B cells with a concomitant down-regulation of T-bet, IL-12Rbeta2, and IFN-gamma. Up-regulation of IL-4 in the Be2 cells is dependent on both T cells and IL-4 as IL-4Ralpha-deficient B cells primed with Th2 cells did not transcribe IL-4, and B cells primed in the presence of IL-4-deficient Th2 cells produced IFN-gamma instead of IL-4. Likewise, the in vivo development of IL-4-expressing B cells in a nematode infection model was dependent on both T cells and IL-4Ralpha-mediated signals. Thus, the differentiation of naive B cells into IL-4-expressing Be2 cells is regulated by a combination of T cell-dependent signals and the cytokine environment and this process is critically dependent upon the IL-4/IL-4R signaling pathway.