IL-2 Responsiveness Research Articles

136: Signal transducer and activator of transcription 3 induction and function in NK cells during murine cytomegalovirus infection

Cytokines induced upon viral infection promote NK cell functions, including their capacity to kill infected cells and produce IFN-gamma, for defense. A subset of these signal through the signal transducers and activators of transcription (STATs). There are a total of seven STAT molecules and although cytokines have preferred STAT pathways, they can conditionally activate alternative STATs. Focusing on STAT1 and STAT4, previous work in this laboratory has demonstrated that STAT levels are differentially regulated in particular cell types, and that cytokine activation of specific STAT pathways is influenced by the concentrations available to shape functional outcomes. The current studies were initiated to extend characterization to STAT3 access and function in mouse NK cells. Basally, NK cells showed a unique STAT3 activation profile with strong stimulation of phosphorylation by IL-10, weaker responses to IFN-alpha and IL-12, and no detectable response to IFN-gamma or IL-6. Ex vivo stimulation of NK cells from murine cytomegalovirus (MCMV)-infected mice with IFN-alpha and IL-12 showed that IL-12 had surprisingly enhanced access to STAT3 by day 1.5 of infection. Induction of increased STAT3 protein levels, depending on type 1 IFN but not IL-12 responsiveness, accompanied the elevated STAT3 activation and was required for the enhanced IL-12 stimulation. NK cells are unique in their high basal expression of STAT4, and IL-12 activation of STAT3 was elevated in NK cells isolated from either uninfected or MCMV-infected STAT4-deficient mice. Taken together, the results extend the observations that basal and induced concentrations of particular STATs shape cytokine pathways to STAT3 stimulation. Ongoing studies are further characterizing the molecular pathways regulating STAT3 expression and function. Overall, the work is advancing understanding of the flexibility for accessing particular STATs to shape cytokine effects during ongoing immune responses to infection. (Supported by the National Institutes of Health, USA.)

TCR triggering modulates the responsiveness and homeostatic proliferation of CD4+ thymic emigrants to IL-7 therapy

AbstractInterleukin-7 (IL-7) is currently used in clinical trials to augment T-cell counts. Paradoxically, elevated systemic IL-7 found in lymphopenic humans is typically insufficient for CD4+ T-cell regeneration, and thymopoiesis becomes critical in this process. Here we show that the proliferative effect of IL-7 is more pronounced on CD4+CD8− thymocytes compared with peripheral CD4+ T cells. These cells express miR181a at higher levels and respond to lower concentrations of IL-7. As single-positive CD4+ thymocytes (CD4+SPT) exit the thymus, they rapidly diminish their proliferation to IL-7 therapy, and this is mediated, at least in part, by major histocompatibility complex class II distribution outside the thymus. Interestingly, increasing T-cell receptor (TCR) stimulation augments IL-7 responsiveness and proliferation of peripheral CD4+ T cells, whereas failure to stimulate TCR abrogates proliferation induced by IL-7. Finally, we demonstrated that IL-7 enhances the proliferation of CD4+ T cells that undergo “slow proliferation” in lymphopenic hosts. To date, our results indicate that TCR signaling is a major controlling factor for CD4 responsiveness and proliferation to IL-7 therapy.

Postthymic Expansion in Human CD4 Naive T Cells Defined by Expression of Functional High-Affinity IL-2 Receptors

As the thymus involutes with age, the maintenance of peripheral naive T cells in humans becomes strongly dependent on peripheral cell division. However, mechanisms that orchestrate homeostatic division remain unclear. In this study we present evidence that the frequency of naive CD4 T cells that express CD25 (IL-2 receptor α-chain) increases with age on subsets of both CD31(+) and CD31(-) naive CD4 T cells. Analyses of TCR excision circles from sorted subsets indicate that CD25(+) naive CD4 T cells have undergone more rounds of homeostatic proliferation than their CD25(-) counterparts in both the CD31(+) and CD31(-) subsets, indicating that CD25 is a marker of naive CD4 T cells that have preferentially responded to survival signals from self-Ags or cytokines. CD25 expression on CD25(-) naive CD4 T cells can be induced by IL-7 in vitro in the absence of TCR activation. Although CD25(+) naive T cells respond to lower concentrations of IL-2 as compared with their CD25(-) counterparts, IL-2 responsiveness is further increased in CD31(-) naive T cells by their expression of the signaling IL-2 receptor β-chain CD122, forming with common γ-chain functional high-affinity IL-2 receptors. CD25 plays a role during activation: CD25(+) naive T cells stimulated in an APC-dependent manner were shown to produce increased levels of IL-2 as compared with their CD25(-) counterparts. This study establishes CD25(+) naive CD4 T cells, which are further delineated by CD31 expression, as a major functionally distinct immune cell subset in humans that warrants further characterization in health and disease.

Cutting Edge: Cell-Autonomous Control of IL-7 Response Revealed in a Novel Stage of Precursor B Cells

During early stages of B-lineage differentiation in bone marrow, signals emanating from IL-7R and pre-BCR are thought to synergistically induce proliferative expansion of progenitor cells. Paradoxically, loss of pre-BCR-signaling components is associated with leukemia in both mice and humans. Exactly how progenitor B cells perform the task of balancing proliferative burst dependent on IL-7 with the termination of IL-7 signals and the initiation of L chain gene rearrangement remains to be elucidated. In this article, we provide genetic and functional evidence that the cessation of the IL-7 response of pre-B cells is controlled via a cell-autonomous mechanism that operates at a discrete developmental transition inside Fraction C' (large pre-BII) marked by transient expression of c-Myc. Our data indicate that pre-BCR cooperates with IL-7R in expanding the pre-B cell pool, but it is also critical to control the differentiation program shutting off the c-Myc gene in large pre-B cells.

Cell-to-Cell Variability Analysis Dissects the Plasticity of Signaling of Common γ Chain Cytokines in T Cells

Natural variability in the abundance of signaling regulators can lead to divergence in cell fate, even within genetically identical cells that share a common differentiation state. We introduce cell-to-cell variability analysis (CCVA), an experimental and computational methodology that quantifies the correlation between variability in signaling regulator abundance and variation in the sensitivity of cells to stimuli. With CCVA, we investigated the unexpected effects of the interleukin 2 (IL-2) receptor α chain (IL-2Rα) on the sensitivity of primary mouse T lymphocytes to cytokines that signal through receptors that have the common γ chain (γ(c)). Our work showed that increased IL-2Rα abundance decreased the concentration of IL-2 required for a half-maximal activation (EC(50)) of the downstream effector signal transducer and activator of transcription 5 (STAT5), but reduced the responsiveness to IL-7 or IL-15, without affecting the EC(50) values of other γ(c) cytokines. To investigate the mechanism of the effect of IL-2Rα on γ(c) cytokine signaling, we introduced a Bayesian-inference computational framework that models the formation of receptor signaling complexes with data from previous biophysical measurements. With this framework, we found that a model in which IL-2Rα drives γ(c) depletion through the assembly of functional IL-2R complexes was consistent with both the CCVA data and experimental measurements. The combination of CCVA and computational modeling produced quantitative understanding of the crosstalk between γ(c) cytokine receptor signaling in T lymphocytes.

Decreased IL-7 responsiveness is related to oxidative stress in HIV disease.

HIV disease results in decreased IL-7 receptor expression and IL-7 responsiveness in T cells. To explore mechanisms of these deficiencies, we compared CD127 expression and IL-7 induction of P-STAT5 in T cells from HIV-infected persons with serum concentrations of cytokines (IL-7, IL-6 and IL-15), markers of microbial translocation (sCD14 and LPS), and with an indicator of oxidative stress (malondialdehyde (MDA) adducts). CD127 expression was directly related to IL-7 responsiveness in most CD8+ T cell subsets but not in CD4+ T cells from HIV-infected persons. MDA adducts were increased in serum of HIV-infected patients and were inversely related to IL-7 responsiveness in CD8+ T cells and in central memory CD4+ T cells. Incubation of T cells from healthy controls with hydrogen peroxide resulted in impairments in IL-7 induction of P-STAT5. These findings suggest that oxidative stress that is characteristic of HIV disease could contribute to impairments in IL-7 responsiveness and disrupt T cell homeostasis.

Ceramide formation is involved in Lactobacillus acidophilus-induced IFN-beta response in dendritic cells

Event Abstract Back to Event Ceramide formation is involved in Lactobacillus acidophilus-induced IFN-beta response in dendritic cells Eva Fuglsang1*, Louise Henningsen1 and Hanne Frøkiær1 1 University of Copenhagen, Department of Veterinary Disease Biology, Denmark The sphingolipid ceramide is known to play a role in lipid raft fusion and receptor clustering in the plasma membrane (PM). Upon bacterial encounter, dendritic cells (DCs) endocytose the bacteria and initiate a bacteria-specific downstream signaling event. We hypothesized that conversion of sphingomyelin to ceramide by acid sphingomyelinase (ASMase) at the outer leaflet of the PM is a key event in endocytosis of gram-positive Lactobacillus acidophilus (L. acidophilus) and the subsequent induction of IFN-beta in DCs and, as the gram-negative Escherichia coli (E. coli) does not induce appreciable amounts of IFN-beta, the ASMase activity would affect endocytosis and the ensuing cytokine response of L. acidophilus and E. coli differently. SMase or an inhibitor of ASMase and acid ceramidase, chlorpromazine (CPZ), was added to DCs prior to stimulation with either of the bacteria. Endocytosis of fluorescent bacteria +/- FITC-dextran was measured by flow cytometry and gene expression and cytokine response of IFN-beta and IL-12 was measured by qPCR and ELISA, respectively. Addition of SMase increased the uptake of L. acidophilus and L. acidophilus-induced IL-12/IFN-beta but showed no effect on the uptake of E. coli though decreasing IL-12 induced by E. coli. SMase also showed to down-regulate Pam3CSK4-induced macropinocytosis of both bacteria. Addition of CPZ increased actin-dependent uptake of dextran and increased Il-12/Ifn-beta expression induced by L. acidophilus, thus further substantiating the key role of ceramide and thus, phagocytosis, in L. acidophilus-induced IL-12/IFN-beta. Keywords: Dendritic Cells, ceramide, Endocytosis, Lactobacillus acidophilus, Escherichia coli Conference: 15th International Congress of Immunology (ICI), Milan, Italy, 22 Aug - 27 Aug, 2013. Presentation Type: Abstract Topic: Innate immunity Citation: Fuglsang E, Henningsen L and Frøkiær H (2013). Ceramide formation is involved in Lactobacillus acidophilus-induced IFN-beta response in dendritic cells. Front. Immunol. Conference Abstract: 15th International Congress of Immunology (ICI). doi: 10.3389/conf.fimmu.2013.02.01028 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 11 Jul 2013; Published Online: 22 Aug 2013. * Correspondence: Miss. Eva Fuglsang, University of Copenhagen, Department of Veterinary Disease Biology, Frederiksberg, 1870, Denmark, efu@sund.ku.dk Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Eva Fuglsang Louise Henningsen Hanne Frøkiær Google Eva Fuglsang Louise Henningsen Hanne Frøkiær Google Scholar Eva Fuglsang Louise Henningsen Hanne Frøkiær PubMed Eva Fuglsang Louise Henningsen Hanne Frøkiær Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

IL-4 has a critical, mouse strain-limited role in innate memory CD8+ T cell development. (115.19)

Abstract Mice have large numbers of innate memory cells: CD8+ T cells that develop functional and phenotypic memory cell characteristics in the absence of purposeful immunization. The role of IL-4 production by iNKT cells in innate memory cell development is shown by an ~80% decrease in splenic memory phenotype CD8+ T cell number in IL-4-, IL-4Rα-, Stat6- and CD1d KO BALB/c mice and an ~1/3 normal basal IL-4 level in CD1d KOs. The stimulatory effect of IL-4 on innate memory cell development is first observed in CD8hiCD4lo thymocytes and persists through adulthood. Anti-IL-4 mAb decreases innate memory cell number in thymus and spleen in immature mice, but only in thymus in adults. In contrast to BALB/c mice, IL-4Rα deficiency has little effect on CD8+ memory phenotype T cell number in C57BL/6 mice. This BALB/c - C57BL/6 difference is not associated with appreciable differences in basal total body or thymic IL-4 expression, CD8+ T cell IL-4Rα expression or IL-4 responsiveness, but is associated with greater IL-15Rα and IL-2/15Rβ expression and IL-15 responsiveness by C57BL/6 than BALB/c CD8+ splenocytes. In 5 additional mouse strains studied, 3 resemble BALB/c and 2 resemble C57BL/6 mice with regard to the IL-4 stimulation of innate memory cell development; an IL-4 effect correlates positively with thymic memory phenotype CD8+ T cell number. Thus, IL-4 produced by thymic NKT cells has a major role in memory phenotype CD8+ T cell development that varies among mouse strains.

The role of soluble IL-7 receptor α in murine CD8+ T-cell responses (105.22)

Abstract The expression of membrane-bound IL-7 receptor α (CD127) is reduced in many viral infections. In HIV infection, this downregulation may be explained in part by increased plasma levels of a soluble form of CD127 (sCD127). We and others have shown that the activity of human IL-7 and cytotoxic CD8+T-cell (CTL) function is decreased by sCD127 in vitro. Observed impairment of IL-7 activity in HIV infection may contribute to the decline of CTL function. The role of sCD127 in such immunopathogenesis is not known. Determining the role of sCD127-mediated immune modulation necessitates the use of an in vivo model. The effect of sCD127 on the IL-7 response of murine splenic CD8+T-cells was evaluated. CFSE-labeled naïve CD8+T-cells were incubated with medium, IL-7 or pre-complexed IL-7 + sCD127 and cell proliferation was assessed. Unlike human T-cells, the survival of murine T-cells in vitro is dependent on the addition of γ-chain receptor cytokines to the culture medium. Cells cultured with sCD127 + IL-7 were less viable and proliferated less (as measured by cell division) compared to IL-7 alone. Our results indicate that sCD127 inhibits the activity of IL-7 on murine naïve CD8+T-cells in vitro, confirming previous results in human T-cell culture. These data suggest that the biological activity of sCD127 on CD8+T-cells is similar between mice and humans, thus providing rationale for the further study of sCD127 in established murine models of CD8+T-cell-mediated responses to infection.

Type 1 Diabetes-Associated IL2RA Variation Lowers IL-2 Signaling and Contributes to Diminished CD4+CD25+ Regulatory T Cell Function

Numerous reports have demonstrated that CD4(+)CD25(+) regulatory T cells (Tregs) from individuals with a range of human autoimmune diseases, including type 1 diabetes, are deficient in their ability to control autologous proinflammatory responses when compared with nondiseased, control individuals. Treg dysfunction could be a primary, causal event or may result from perturbations in the immune system during disease development. Polymorphisms in genes associated with Treg function, such as IL2RA, confer a higher risk of autoimmune disease. Although this suggests a primary role for defective Tregs in autoimmunity, a link between IL2RA gene polymorphisms and Treg function has not been examined. We addressed this by examining the impact of an IL2RA haplotype associated with type 1 diabetes on Treg fitness and suppressive function. Studies were conducted using healthy human subjects to avoid any confounding effects of disease. We demonstrated that the presence of an autoimmune disease-associated IL2RA haplotype correlates with diminished IL-2 responsiveness in Ag-experienced CD4(+) T cells, as measured by phosphorylation of STAT5a, and is associated with lower levels of FOXP3 expression by Tregs and a reduction in their ability to suppress proliferation of autologous effector T cells. These data offer a rationale that contributes to the molecular and cellular mechanisms through which polymorphisms in the IL-2RA gene affect immune regulation, and consequently upon susceptibility to autoimmune and inflammatory diseases.

Intravenous tolerance effectively overcomes enhanced pro-inflammatory responses and experimental autoimmune encephalomyelitis severity in the absence of IL-12 receptor signaling

Intravenous (i.v.) administration of autoantigen effectively induces Ag-specific tolerance against experimental autoimmune encephalomyelitis (EAE). We and others have shown enhanced EAE severity in mice lacking IL-12 or its receptor, strongly suggesting an immunoregulatory effect of IL-12 signaling. To examine the role of IL-12 responsiveness in autoantigen-induced tolerance in EAE, we administered autoantigen i.v. in two distinct treatment regimes to wildtype and IL-12Rβ2−/− mice, immunized to develop EAE. Administration at the induction phase suppressed EAE in wildtype and IL-12Rβ2−/− mice however the effect was somewhat less potent in the absence of IL-12Rβ2. Expression of pro-inflammatory cytokines such as IFN-γ, IL-17 and IL-2, was inhibited in wild-type tolerized mice but less so in IL-12Rβ2−/− mice. I.v. antigen was also effective in suppressing disease in both genotypes when given during the clinical phase of disease with similar CNS inflammation, demyelination and peripheral inflammatory cytokine profiles observed in both genotypes. There was however a mild impact of a lack of IL-12 signaling on Treg induction during tolerance induction compared to WT mice in this treatment regime. These findings show that the enhanced severity of EAE that occurs in the absence of IL-12 signaling can be effectively overcome by i.v. autoantigen, indicating that this therapeutic effect is not primarily mediated by IL-12 and that i.v. tolerance could be a powerful approach in suppressing severe and aggressive MS.

IL-15–High-Responder Developing NK Cells Bearing Ly49 Receptors in IL-15−/− Mice

In mice lacking IL-15, NK cell development is arrested at immature stages, providing an opportunity to investigate the earliest developing NK cells that would respond to IL-15. We show in this study that immature NK cells were present in the spleen as well as bone marrow (BM) and contained IL-15-high-responder cells. Thus, mature NK cells were generated more efficiently from IL-15(-/-) than from control donor cells in radiation BM chimeras, and the rate of IL-15-induced cell division in vitro was higher in NK cells in the spleen and BM from IL-15(-/-) mice than in those from wild-type mice. Phenotypically, NK cells developed in IL-15(-/-) mice up to the minor but discrete CD11b(-)CD27(+)DX5(hi)CD51(dull)CD127(dull)CD122(hi) stage, which contained the majority of Ly49G2(+) and D(+) NK cells both in the spleen and BM. Even among wild-type splenic NK cells, IL-15-induced proliferation was most prominent in CD11b(-)DX5(hi) cells. Notably, IL-15-mediated preferential expansion (but not conversion from Ly49(-) cells) of Ly49(+) NK cells was observed in vitro only for NK cells in the spleen. These observations indicated the uneven distribution of NK cells of different developing stages with variable IL-15 responsiveness in these lymphoid organs. Immature NK cells in the spleen may contribute, as auxiliaries to those in BM, to the mature NK cell compartment through IL-15-driven extramarrow expansion under steady-state or inflammatory conditions.

Tipifarnib-mediated suppression of T-bet-dependent signaling pathways

Large granular lymphocyte (LGL) leukemia is a chronic lymphoproliferative disease in which T-bet [T-box transcription factor 21 gene (tbx21)] overexpression may play a pathogenic role. T-bet orchestrates the differentiation of mature peripheral T-cells into interferon-γ (IFN-γ) and tumor necrosis factor-α producing CD4+ T-helper type I (Th1) and CD8+ T cytotoxic cells that are necessary for antiviral responses. When IL-12 is produced by antigen-presenting cells, T-bet expression is induced, causing direct stimulation of ifng gene transcription while simultaneously acting as a transcriptional repressor of the IL4 gene, which then leads to Th1 dominance and T-helper type 2 differentiation blockade. Additionally, T-bet has been shown to regulate histone acetylation of the ifng promoter and enhancer to loosen condensed DNA, creating greater accessibility for other transcription factor binding, which further amplifies IFNγ production. We found that treatment with a farnesyltransferase inhibitor tipifarnib reduced Th1 cytokines in LGL leukemia patient T-cells and blocked T-bet protein expression and IL-12 responsiveness in T-cells from healthy donors. The mechanism of suppression was based on modulation of histone acetylation of the ifng gene, which culminated in Th1 blockade.

HIV infection of thymocytes inhibits IL-7 activity without altering CD127 expression

BackgroundThymic function is altered in HIV infection and characterized by dysregulation of the thymic epithelial network, reduced thymic output and ultimately an impaired naïve T-cell pool. The IL-7/IL-7 receptor (IL-7R) signalling pathway is critical for the maturation and differentiation of thymocytes. HIV infection is associated with a decrease in IL-7Rα (CD127) expression and impaired CD127 signalling in circulating CD8+ T-cells; however, little is known about the effect of HIV on CD127 expression and IL-7 activity in the thymus. Therefore, the effect of in vitro HIV infection on CD127 expression and IL-7-mediated function in thymocytes was investigated.FindingsIn vitro HIV infection of thymocytes did not affect CD127 expression on either total thymocytes or on single positive CD4 or single positive CD8 subsets. However, HIV infection resulted in a decrease in the level of IL-7-induced STAT-5 phosphorylation and Bcl-2 expression in unfractionated thymocytes.ConclusionThese findings indicate that HIV infection alters IL-7 responsiveness of thymocytes by a mechanism other than CD127 downregulation and potentially explain the disruption in thymopoiesis observed in HIV infection.

Decreased IL-7 Signaling in T Cells From Patients With PTLD After Allogeneic HSCT

Interleukin (IL)-7, a nonredundant cytokine for B and T cells, plays a central role in cell survival and immune memory formation. Peripheral blood mononuclear cells (PBMCs) from 7 patients after hematopoietic stem cell transplantation (HSCT) diagnosed with posttransplantation lymphoproliferative disease (PTLD) and from 10 Epstein-Barr virus (EBV) polymerase chain reaction-positive HSCT patients (controls) were evaluated for IL-7- and IL-2 induced Stat5 phosphorylation in CD4+ and CD8+ T cells. PBMCs from PTLD+ and control patients exhibited detectable EBV specific CD8+ T cells defined by tetramer analysis. CD4+ and CD8+ T cells from patients with PTLD showed statistically significant reduction in responsiveness to IL-7 compared with PBMCs obtained from controls defined by Stat5 phosphorylation. CD20+ B cells from patients with PTLD and from some EBV+ polymerase chain reaction control individuals exhibited IL-7R expression. Dysregulated immune surveillance, reflected by deficient Stat5 phosphorylation, may facilitate PTLD development despite the presence of EBV-reactive CD8+ T cells. Reduced IL-7 responsiveness will aid to monitor patients after HSCT for increased risk to develop EBV-associated PTLD.

IL-2 limits IL-12 enhanced lymphocyte proliferation during Leishmania amazonensis infection

C3H mice infected with Leishmania amazonensis develop persistent, localized lesions with high parasite loads. During infection, memory/effector CD44 hiCD4 + T cells proliferate and produce IL-2, but do not polarize to a known effector phenotype. Previous studies have demonstrated IL-12 is insufficient to skew these antigen-responsive T cells to a functional Th1 response. To determine the mechanism of this IL-12 unresponsiveness, we used an in vitro assay of repeated antigen activation. Memory/effector CD44 hiCD4 + T cells did not increase proliferation in response to either IL-2 or IL-12, although these cytokines upregulated CD25 expression. Neutralization of IL-2 enhanced CD4 + T cell proliferation in response to IL-12. This cross-regulation of IL-12 responsiveness by IL-2 was confirmed in vivo by treatment with anti-IL-2 antibodies and IL-12 during antigen challenge of previously infected mice. These results suggest that during chronic infection with L. amazonensis, IL-2 plays a dominant, immunosuppressive role independent of identifiable conventional T reg cells.

An autoimmune-associated variant in PTPN2 reveals an impairment of IL-2R signaling in CD4(+) T cells.

The IL-2/IL-2R signaling pathway plays an important role in autoimmunity. Several genes identified in GWA studies encode proteins in the IL-2/IL-2R signaling cascade that are associated with autoimmune diseases. One of these, PTPN2, encodes a protein tyrosine phosphatase that is highly expressed in T cells and regulates cytokine signaling. An intronic risk allele in PTPN2, rs1893217(C), correlated with decreased IL-2R signaling in CD4+ T cells as measured by phosphorylation of STAT5 (pSTAT5). We modeled an additive SNP genotype, in which each copy of the risk allele conferred a decrease in IL-2R signaling (p=4.4×10−8). Decreased pSTAT5 impacted IL-2Rβ chain signaling resulting in reduced FOXP3 expression in activated cells. This phenotype was not due to overt differences in expression of the IL-2R, molecules in the IL-2R signaling cascade or defects in STAT5. However, the rs1893217(C) risk variant did correlate with decreased PTPN2 expression in CD4+CD45RO T cells (p=0.0002). Thus, the PTPN2rs1893217(C) risk allele associated with reduced pSTAT5 in response to IL-2 and reduced PTPN2 expression. Together, these data suggest that decreased expression of PTPN2 may indirectly modulate IL-2 responsiveness. These findings, identified through genotype/phenotype relationships, may lead to identification of novel mechanisms underlying dysregulation of cytokine signaling in autoimmunity.

IL-7-dependent STAT-5 activation and CD8+ T cell proliferation are impaired in HIV infection

This study tests the hypothesis that IL-7 signaling and activity of CD8(+) T cells are impaired in HIV infection. IL-7 is necessary for optimal CTL activity and T cell survival and proliferation. Defects in IL-7R signaling may contribute to impaired activity of IL-7 observed in progressive HIV disease. A decreased proportion of CD8(+) T cells expressing the IL-7Rα chain (CD127) in progressive HIV disease would be expected to affect IL-7 activity. Alternatively, disease-associated defects of remaining CD8(+)CD127(+) T cells may influence IL-7 responsiveness. Therefore, the IL-7 responsiveness of CD8(+)CD127(+) T cells from HIV(-) and untreated or treated HIV(+) individuals was investigated. Blood was collected from HIV(-) and untreated or effectively treated HIV(+) (<50 viral copies/ml for >1 year) individuals, and CD8(+)CD127(+) T cells were isolated and cultured with IL-7. Indicators of IL-7 signaling (P-STAT5) and activity (Bcl-2 and proliferation) were evaluated by flow cytometry. Isolated CD8(+)CD127(+) T cells from untreated HIV(+) individuals expressed significantly less P-STAT5 in response to IL-7 compared with CD8(+)CD127(+) T cells from HIV(-) individuals. In effectively treated HIV(+) individuals, CD8(+)CD127(+) T cells also expressed significantly lower levels of P-STAT5 compared with HIV(-) individuals. IL-7-dependent proliferation of CD8(+)CD127(+) T cells from untreated HIV(+) individuals was similarly impaired. In contrast, IL-7-induced Bcl-2 expression was not impaired in CD8(+)CD127(+) T cells from HIV(+) individuals. These data demonstrate that IL-7/IL-7R dysfunction in HIV infection may contribute to IL-7-specific signaling defects. Decreased, IL-7-dependent activation of STAT5 and impaired proliferation may negatively impact the maintenance of CD8(+) T cell responsiveness in HIV infection.

PS1-32 Decreased IL-7 responsiveness of T lymphocytes in patients with idiopathic CD4 lymphopenia

PS1-32 Decreased IL-7 responsiveness of T lymphocytes in patients with idiopathic CD4 lymphopenia

TCF-1 Flips the Switch on Eomes

The interaction between different transcriptional pathways in CD8(+) T cell memory remains incompletely understood. In this issue, Zhou et al. (2010) demonstrate an important role for T cell factor 1 in regulating CD8(+) T cell memory via control of a second transcription factor, Eomesodermin.