Signal transduction via the T cell antigen receptor in naïve and effector/memory T cells

T cells play an indispensable role in immune defense against infectious agents, but can also be pathogenic. These T cells develop in the thymus, are exported into the periphery as naïve cells and participate in immune responses. Upon recognition of antigen, they are activated and differentiate into effector and memory T cells. While effector T cells carry out the function of the immune response, memory T cells can last up to the life time of the individual, and are activated by subsequent antigenic exposure. Throughout this life cycle, the T cell uses the same receptor for antigen, the T cell Receptor, a complex multi-subunit receptor. Recognition of antigen presented by peptide/MHC complexes on antigen presenting cells unleashes signaling pathways that control T cell activation at each stage. In this review, we discuss the signals regulated by the T cell receptor in naïve and effector/memory T cells.

A Polymerase mechanism-based strategy for viral attenuation and vaccine development

Live, attenuated vaccines have prevented morbidity and mortality associated with myriad viral pathogens. Development of live, attenuated vaccines has traditionally relied on empirical methods, such as growth in nonhuman cells. These approaches require substantial time and expense to identify vaccine candidates and to determine their mechanisms of attenuation. With these constraints, at least a decade is required for approval of a live, attenuated vaccine for use in humans. We recently reported the discovery of an active site lysine residue that contributes to the catalytic efficiency of all nucleic acid polymerases (Castro, C., Smidansky, E. D., Arnold, J. J., Maksimchuk, K. R., Moustafa, I., Uchida, A., Götte, M., Konigsberg, W., and Cameron, C. E. (2009) Nat. Struct. Mol. Biol. 16, 212-218). Here we use a model RNA virus and its polymerase to show that mutation of this residue from lysine to arginine produces an attenuated virus that is genetically stable and elicits a protective immune response. Given the conservation of this residue in all viral polymerases, this study suggests that a universal, mechanism-based strategy may exist for viral attenuation and vaccine development.

Regulation of T-cell responses and disease by tec kinase Itk

Itk is a member of the Tec family tyrosine kinases involved in T-cell receptor signaling. The authors review the background and most recent findings of the role of Itk T-cell activation and development of αβ T cells. They also discuss the role of Itk in development of nonconventional T cells, including CD8(+) innate memory phenotype T cells, different γδ T-cell populations, and invariant NKT cells. They close by reviewing the regulation of T helper differentiation and cytokine secretion, the immune response to infectious disease, and diseases such as allergic asthma and atopic dermatitis by Itk.

Complex role for IL-2 Inducible T cell kinase (Itk) in T helper 1 and T helper 2 differentiation and function (163.18)

T helper responses are critical for a productive immune response but an inappropriate response results in inflammatory and autoimmune disorders. There are still considerable gaps in our knowledge of pathways that regulate differentiation of T helper subsets. IL-2 Inducible T cell kinase (Itk) is primarily expressed in T cells and is critical for their development, activation and function. Here, we show that Itk regulates two distinct signals during T helper differentiation. The first signal represses IFNγ independent of Tbet and maintains naïve T cells in an unbiased state, until it comes in contact with cognate antigen. This signal controls epigenetic processes that maintains the IFNγ locus closed and is critical for induction of Th2 transcriptional program. The second signal occurs following T cell activation, and is critical for secretion of Th1, Th2 and Th17 cytokines. As a result, Itk-/- mice are not only defective in Th2 responses, but are also more susceptible to infection by Th1 inducing intracellular pathogen T. Gondii. More importantly, these signaling pathways are conserved in humans, as loss of Itk in human PBMC derived T cells and Jurkat cells results in a substantial reduction in the secretion of a number of effector cytokines, at least partly due to a failure to activate pERK. This work has implications for understanding T helper differentiation programs, and Itk as a therapeutic target for Th2 mediated inflammatory and Th1/ Th17 mediated autoimmune disorders

Mast cell specific negative regulation of LPS induced pro-inflammatory response by Itk and Btk (177.20)

Gram-negative bacterial endotoxin lipopolysaccharide (LPS) induces mast cell secretion of pro-inflammatory cytokines such as tumor necrosis factor (TNF)-α, which is responsible for septic hypothermia. The non receptor tyrosine kinases Itk and Btk are both expressed in mast cells, and act as signaling regulators, but their roles in the response of mast cells to LPS are unclear. Here we show that Itk/Btk double knockout (DKO) mice suffered exacerbated and prolonged LPS induced hypothermia with increased TNF-α production by mast cells, compared to WT, Itk-/- and Btk-/- mice. This aggravated LPS induced hypothermia was recapitulated in mast cell deficient Sash mice reconstituted with DKO bone marrow derived mast cells (BMMCs). LPS (TLR4 ligand) stimulated DKO BMMCs exhibited hyperactive pro-inflammatory cytokine production with severely altered NF-κB signaling, which was not observed with Pam3CSK4 (TLR1/2 ligand). By contrast, DKO bone marrow derived macrophage and dendritic cells were not hyper-responsive to LPS as observed in DKO BMMCs, suggesting that Itk and Btk act as mast cell specific negative regulators in LPS/TLR4 signaling. Microarray analysis further revealed that the absence of Itk and Btk in mast cells significantly enhanced LPS induced pro-inflammatory program, which could potentially deteriorate endotoxin induced mast cell mediated inflammatory diseases.

Itk and antigen specific CD8+ T cell memory differentiation (110.8)

It has been shown that Itk, a Tec kinase family member, is important for T cell development and differentiation. CD4+ and CD8+ T cells in Itk-/- mice display innate memory phenotype. Since Itk-/- CD8+ T cells preferentially develop into innate memory T cells in thymus, we aimed to determine whether naïve Itk-/- CD8+ T cells also preferentially differentiate into memory T cells after primary response to foreign antigens. To study the intrinsic and extrinsic effects of Itk in naïve CD8+ T cell differentiation into memory T cells, we used an OVA-Listeria monocytogenes infection model in which naïve OTI Rag1-/- T cells or OTI Itk-/- Rag1-/- T cells were adoptively transferred into Itk-/- or WT recipient mice. We found that naïve OTI ITK-/- Rag1-/- T cells have comparable ability to WT OTI Rag-/- T cells in memory T cell differentiation after a 5-week infection in WT hosts. In contrast, WT OTI Rag1-/- T cells are deficient in differentiating into memory T cells when placed in Itk-/- hosts. Although Itk affects the CD8+ T cell development in the thymus, its absence does not affect antigen specific CD8+ memory T cell differentiation. However, Itk-/- mice have an impaired environment for naïve CD8+ T cells differentiation into memory T cells during L. monocytogenes infection. These results suggest that Itk expression in cells other than CD8+ T cells is critical for supporting the antigen specific CD8+ T cell memory differentiation.

Effect of Selective Aryl Hydrocarbon Receptor Modulators on a murine model of Th17 driven Hypersensitivity Pneumonitis (HP) (163.21)

The physiological role of Aryl Hydrocarbon Receptor (AhR) in immune response remains a key question after the discovery that AhR is an essential transcription factor for Th17 differentiation. To study the role of AhR in T cell differentiation we examined the effects of Selective AhR Modulators (SAhRMs) on antigen specific T cell response in vitro. We found that as expected, an AhR agonist enhances IL-17A production whereas a SAhRM suppresses it. However, we also found that AhR agonists suppressed production of IL-4, which was induced by the SAhRM. By contrast IFNγ was inhibited by both compounds. We also examined the effect of SAhRMs on a well established Th17 driven murine model of hypersensitivity pneumonitis mediated by a thermophile Staphylopolyspora rectivirgula (SR). Treatment of mice that have developed SR driven airway inflammation with an AhR partial antagonist or an antagonist, suppressed AhR activation in the lung. However, these AhR ligands also increased the production IL-4 by T cells in the lung, with an increase in the percentage of T cells that produce both IL-17A and IL-4. By contrast, these ligands did not suppress IFNγ or IL-17A production. Analysis of cytokine transcripts in lungs confirmed these data. This suggests that although AhR activation is required for Th17 differentiation, once cells commit to Th17 lineage, inhibiting AhR may not affect Th17 cytokine production, but may enhance the ability of these cells to produce IL-4.

Abstract 1649: Genome-wide association study of copy number variations in serous epithelial ovarian cancer susceptibility

DNA copy number variations (CNVs) are a significant and ubiquitous source of human genetic variation. However, the influence of CNVs on cancer susceptibility remains poorly understood. Out of 83 genome-wide association studies (GWAS) on cancer to date, only a few studies found significant associations on germline CNVs and cancer. Here we analyzed data from our ongoing two-stage GWAS of four North American case-control studies to test the hypothesis that CNVs in germline DNA from peripheral blood lymphocytes may serve as risk factors for epithelial ovarian cancer (EOC). To reduce disease heterogeneity, we focused on the subset of cases with serous histology. The analysis was therefore based on 942 serous ovarian cancer patients and 1,682 healthy controls who were genotyped using the Illumina 610K quad array. Subjects with extreme noise and genomic waviness in log R ratio (LR) were excluded prior to segmentation; principal component analysis was performed to adjust for batch effects. CNV segmentation was performed on LR data from 22 autosomes using circular binary segmentation embedded in the Copy Number Analysis Module from Golden Helix SNP Variation Suite version 7. Copy number segment covariates were discretized based on the thresholds that signify a transition between copy number states (deletion/no deletion; duplication/no duplication) after the segmentation. Unconditional logistic regression on a log-additive model was used to evaluate the association between copy number states and serous EOC risk after adjusting for study sites. By comparing single marker copy number states at 388,958 SNPs on 22 autosomes, we observed a total of 134 SNPs significantly associated with risk of serous EOC with a p value below 10−6. Associations with deletion polymorphisms were observed on chromosomes 7, 8, 14, and 18 when controlling for false discovery rate at 1%; no duplication polymorphisms were significant. We observed a large deletion at chromosome 14 that occurred in 8.9% of cases but in only 3.9% of controls, with a p value of 5.59×10−8 (Odds Ratio (OR): 2.56, 95% confidence interval (CI): 1.82-3.60). Another common deletion on chromosome 7 occurred in 8.8% of cases and only 4.3% of controls (p=3.83×10−6; OR: 2.23, 95% CI: 1.60-3.10). Two additional regions on chromosomes 8 and 18 with deletion events less than 5% were also identified. Women who harbored the deletion on chromosome 8 were at lower risk of developing serous ovarian cancer (p=4.83×10−8; OR: 0.04, 95% CI: 0.01-0.30). Women who carried the deletion on chromosome 18 had an increased risk for serous EOC (p=9.04×10−7; OR: 7.26, 95% CI: 2.94-17.97). Further validation of these four regions using independent data sets is currently underway. In summary, this is the largest reported genome-wide study of CNVs and serous EOC risk. These preliminary results suggested that germline CNVs may play an important role in ovarian cancer susceptibility.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1649. doi:1538-7445.AM2012-1649

A unique role for ITK in survival of invariant NKT cells associated with the p53-dependent pathway in mice

Invariant NKT (iNKT) cells play important roles in the immune response. ITK and TXK/RLK are Tec family kinases that are expressed in iNKT cells; the expression level of ITK is ∼7-fold higher than that of TXK. Itk(-/-) mice have reduced iNKT cell frequency and numbers, with defects in development and cytokine secretion that are exacerbated in Itk/Txk double-knockout mice. In contrast, there is no iNKT cell defect in Txk(-/-) mice. To determine whether ITK and TXK play distinct roles in iNKT cell development and function, we examined mice that overexpress TXK in T cells at levels similar to Itk. Overexpression of TXK rescues the maturation and cytokine secretion of Itk(-/-) iNKT cells, as well as altered expression of transcription factors T-bet, eomesodermin, and PLZF. In contrast, the increased apoptosis observed in Itk(-/-) splenic iNKT cells is not affected by TXK overexpression, likely due to the lack of effect on the elevated expression of p53 regulated proapoptotic pathways Fas, Bax, and Bad in those cells. Supporting this idea, p53(-/-) and Bax(-/-) mice have increased splenic iNKT cells. Our results suggest that TXK plays an overlapping role with ITK in iNKT cell development and function but that ITK also has a unique function in the survival of iNKT cells, likely via a p53-dependent pathway.

Structure and function of Tec family kinase Itk

Itk is a member of the Tec family of kinases that is expressed predominantly in T cells. Itk regulates the T cell receptor signaling pathway to modulate T cell development and T helper cell differentiation, particularly Th2 differentiation. Itk is also important for the development and function of iNKT cells. In this review we discuss current progress on our understanding of the structure, activation and signaling pathway of Itk, in addition to inhibitors that have been developed, which target this kinase. We also place in context the function of Itk, available inhibitors and potential use in treating disease.

Structural requirements for the inhibition of calcium mobilization and mast cell activation by the pyrazole derivative BTP2

Mast cells play a critical role in the development of the allergic response. Upon activation by allergens and IgE via the high affinity receptor for IgE (FcɛRI), these cells release histamine and other functional mediators that initiate and propagate immediate hypersensitivity reactions. Mast cells also secrete cytokines that can regulate immune activity. These processes are controlled, in whole or part, by increases in intracellular Ca(2+) induced by the FcɛRI. We show here that N-(4-(3,5-bis(trifluoromethyl)-1H-pyrazol-1-yl)phenyl)-4-methyl-1,2,3-thiadiazole-5-carboxamide (BTP2), a pyrazole derivative, inhibits activation-induced Ca(2+) influx in the rat basophil cell line RBL-2H3 and in bone marrow-derived mast cells (BMMCs), without affecting global tyrosine phosphorylation of cellular proteins or phosphorylation of the mitogen-activated protein kinases Erk1/2, JNK and p38. BTP2 also inhibits activation-induced degranulation and secretion of interleukin (IL)-2, IL-3, IL-4, IL-6, IL-13, tumor necrosis factor (TNF)-α, and granulocyte macrophage-colony stimulating factor (GM-CSF) by BMMCs, which correlates with the inhibition of Nuclear Factor of Activated T cells (NFAT) translocation. In vivo, BTP2 inhibits antigen-induced histamine release. Structure-activity relationship analysis indicates that substitution at the C3 or C5 position of the pyrazole moiety on BTP2 (5-trifluoromethyl-3-methyl-pyrazole or 3-trifluoromethyl-5-methyl-pyrazole, respectively) affected its activity, with the trifluoromethyl group at the C3 position being critical to its activity. We conclude that BTP2 and related compounds may be potent modulators of mast cell responses and potentially useful for the treatment of symptoms of allergic inflammation.

Structural requirements for the inhibition of calcium mobilization and mast cell activation by the pyrazole derivative BTP2 (107.16)

Cytosolic Ca2+ changes in mast cells are central for driving their activation. Thus, pharmacological tools that inhibit this process represent unique strategies for inhibiting mast cell function and their contribution to disease. We find that the pyrazole compound BTP2 inhibited FcϵRI-triggered sustained Ca2+ influx in RBL-2H3 cells and murine BMMCs with little effect on the tyrosine phosphorylation of cellular proteins. It also did not affect FcϵRI-induced phosphorylation of mitogen-activated protein kinases Erk1/2, JNK, and p38 nor downstream c-fos expression. This suggests that BTP2 inhibits Ca2+ mobilization without affecting the FcϵRI signal transduction cascade. In vitro, BTP2 inhibited FcϵRI-triggered degranulation and cytokine secretion, correlating with inhibition of NFAT nuclear translocation. Consistent with this effect, BTP2 inhibited antigen-induced histamine release in vivo. Analysis of structure-function relationships between the BTP2 parent compound and its derivatives implicate a role for the trifluoromethyl group at both carbon positions 3 and 5 of pyrazole in the inhibition of degranulation of BMMCs, with a more dominant effect evoked by the trifluoromethyl group at C3. In conclusion, our studies indicate that pyrazole compounds can provide the molecular framework for the design of specific inhibitors of Ca2+ entry mechanisms and further BTP2 as a medicinal candidate for the treatment of allergic reactions and other mast cell-mediated diseases.

Itk negatively regulates IFNγ, influencing T helper 2 response in vivo (55.16)

Asthma is a major public health concern affecting millions of people each year. Allergic asthma is a T helper 2 (Th2) cell mediated inflammatory disease characterized by airway inflammation and hyper responsiveness. The Tec family tyrosine kinase Interleukin-2 Inducible T cell kinase (Itk) is primarily expressed in T cells and is critical for development, function and differentiation of T helper cells. Itk-/- mice have a defective Th2 response and are not susceptible to allergic asthma and parasitic worm infections. We observed that naïve CD4+ T cells from Itk-/- mice have substantially increased transcript levels of prototypic Th1 genes. We hypothesized that this upregulation of Th1 genes could negatively regulate polarization to Th2 effector cells. Here, we show that Itk can negatively regulate IFNγ. More importantly, in absence of IFNγ there is a rescue in the expression of Th2 related genes and Th2 mediated allergic asthma in Itk-/- mice. In the absence of Itk, IFNγ levels increase leading to a positive feed-forward loop with T-bet. This is responsible for the inability of CD4+ T cells from Itk-/- mice to optimally induce Th2 transcriptional program and develop a Th2 response upon allergen challenge. In addition to providing mechanistic insight into the observed Th2 defects in Itk-/- mice, this work has implications for understanding Itk as a potential target for Th2 mediated inflammation, T helper differentiation programs and the molecular pathology of asthma.

Itk and Btk regulate mast cell responses to lipopolysaccharide: firing or dampening? (151.18)

LPS induces mast cell derived cytokines such as tumor necrosis factor (TNF) α, to cause septic hypothermia. The non receptor tyrosine kinases Itk and Btk are both expressed as signaling regulators in mast cells, but their roles in mast cell response to LPS are unclear. Here we show that Itk-/- mice exhibited less severe LPS induced hypothermia, with no difference observed in Btk-/- mice, compared to C57BL/6 (WT) mice, strikingly however, Itk/Btk double knockout (DKO) mice suffered exacerbated and prolonged hypothermia. Bone marrow derived mast cells (BMMCs) lacking Itk, Btk or both altered degradation of the NFκB inhibitor IκBα in response to LPS. DKO BMMCs exhibited dramatically reduced degradation of IκBα, but significantly enhanced production of TNFα and other LPS responsive genes, suggesting that Itk and Btk altered NF-κB response to suppress TNFα secretion by BMMCs in response to LPS. Analysis of modified existing computational models for LPS and TNFα stimulation revealed novel NFκB/IκBα signaling dynamics which predict our experimental results in WT BMMCs, suggesting that BMMCs may be a good model to integrate primary and secondary responses against LPS, revealing how stimulation of TLR4 ignites TNFα, which triggers and spreads the flame, activating a regulatory network with negative feedback and feed forward loops. This combination of experimental and computational approach promises to reveal novel roles for Itk and Btk in the regulation of the BMMC response to LPS.

Innate memory phenotype CD8+ T cells exhibit prompt and potent antigen specific response (46.2)

Innate memory phenotype CD8 T cells (IMP CD8+CD44hiCD122int) develop in thymus and carry abundant preformed mRNA for cytokines such as interferon-γ (IFN-γ). These cells rapidly produce IFN-γ when stimulated with PMA/Ionomycin or IL-12/IL-18. Whether they can also contribute to antigen specific responses is unclear, as it is difficult to distinguish them from “true” memory cells. We developed a novel method to derive antigen specific IMP CD8, using murine bone marrow chimeras to separate naïve and IMP antigen specific CD8 T cells recognizing the model antigen ovalbumin (OVA). WT or OTI bone marrow transplanted into irradiated MHCI-/- mice gave rise to predominantly IMP CD8 T cells. By contrast, MHCI-/- or OTIMHCI-/- bone marrow transplanted into irradiated WT mice gave rise to predominantly naïve CD8 T cells. IMP CD8 T cells thus derived significantly up-regulated IFN-γ 6 days post OVA restimulation in vitro, following primary exposure to transgenic Listeria-OVA, compared to analogously derived naïve CD8 T cells alone or WT controls. More importantly, OTI IMP CD8 T cells exhibited significantly enhanced early response to OVA or OVA257-264 peptide without primary stimulation. Our findings indicate that the dynamics of the antigen specific response of IMP CD8 T cells is enhanced compared to antigen specific naïve CD8 T cells. Furthermore, this work provides a promising murine model for future investigation of IMP CD8 T cell memory development and antigen response.

Tec family kinases: Itk signaling and the development of NKT αβ and γδ T cells

The Tec family tyrosine kinase interleukin-2 inducible T-cell kinase (Itk) is predominantly expressed in T cells and has been shown to be critical for the development, function and differentiation of conventional αβ T cells. However, less is known about its role in nonconventional T cells such as NKT and γδ T cells. In this minireview, we discuss evidence for a role for Itk in the development of invariant NKT αβ cells, as well as a smaller population NKT-like γδ T cells. We discuss how these cells take what could be the same signaling pathway regulated by Itk, and interpret it to give different outcomes with regards to development and function.

Absence of Tec family kinases interleukin-2 inducible T cell kinase (Itk) and Bruton's tyrosine kinase (Btk) severely impairs Fc epsilonRI-dependent mast cell responses

Mast cells are critical effector cells in the pathophysiology of allergic asthma and other IgE-mediated diseases. The Tec family of tyrosine kinases Itk and Btk serve as critical signal amplifiers downstream of antigen receptors. Although both kinases are expressed and activated in mast cells following FcεRI stimulation, their individual contributions are not clear. To determine whether these kinases play unique and/or complementary roles in FcεRI signaling and mast cell function, we generated Itk and Btk double knock-out mice. Analyses of these mice show decreased mast cell granularity and impaired passive systemic anaphylaxis responses. This impaired response is accompanied by a significant elevation in serum IgE in Itk/Btk double knock-out mice. In vitro analyses of bone marrow-derived mast cells (BMMCs) indicated that Itk/Btk double knock-out BMMCs are defective in degranulation and cytokine secretion responses downstream to FcεRI activation. These responses were accompanied by a significant reduction in PLCγ2 phosphorylation and severely impaired calcium responses in these cells. This defect also results in altered NFAT1 nuclear localization in double knock-out BMMCs. Network analysis suggests that although they may share substrates, Itk plays both positive and negative roles, while Btk primarily plays a positive role in mast cell FcεRI-induced cytokine secretion.

Computational and experimental analysis reveals a requirement for eosinophil-derived IL-13 for the development of allergic airway responses in C57BL/6 mice

Eosinophils are found in the lungs of humans with allergic asthma, as well as in the lungs of animals in models of this disease. Increasing evidence suggests that these cells are integral to the development of allergic asthma in C57BL/6 mice. However, the specific function of eosinophils that is required for this event is not known. In this study, we experimentally validate a dynamic computational model and perform follow-up experimental observations to determine the mechanism of eosinophil modulation of T cell recruitment to the lung during development of allergic asthma. We find that eosinophils deficient in IL-13 were unable to rescue airway hyperresponsiveness, T cell recruitment to the lungs, and Th2 cytokine/chemokine production in ΔdblGATA eosinophil-deficient mice, even if Th2 cells were present. However, eosinophil-derived IL-13 alone was unable to rescue allergic asthma responses in the absence of competence of other IL-13-producing cells. We further computationally investigate the role of other cell types in the production of IL-13, which led to the various predictions including early and late pulses of IL-13 during airway hyperresponsiveness. These experiments suggest that eosinophils and T cells have an interdependent relationship, centered on IL-13, which regulates T cell recruitment to the lung and development of allergic asthma.

Interleukin-2-inducible T cell kinase (Itk) network edge dependence for the maturation of iNKT cell

Invariant natural killer T (iNKT) cells are a unique subset of innate T lymphocytes that are selected by CD1d. They have diverse immune regulatory functions via the rapid production of interferon-γ (IFN-γ) and interleukin-4 (IL-4). In the absence of signaling nodes Itk and Txk, Tec family non-receptor tyrosine kinases, mice exhibit a significant block in iNKT cell development. We now show here that although the Itk node is required for iNKT cell maturation, the kinase domain edge of Itk is not required for continued maturation iNKT cells in the thymus compared with Itk-null mice. This rescue is dependent on the expression of the Txk node. Furthermore, this kinase domain independent edge rescue correlates with the increased expression of the transcription factors T-bet, the IL-2/IL-15 receptor β chain CD122, and suppression of eomesodermin expression. By contrast, α-galactosyl ceramide induced cytokine secretion is dependent on the kinase domain edge of Itk. These findings indicate that the Itk node uses a kinase domain independent edge, a scaffolding function, in the signaling pathway leading to the maturation of iNKT cells. Furthermore, the findings indicate that phosphorylation of substrates by the Itk node is only partially required for maturation of iNKT cells, while functional activation of iNKT cells is dependent on the kinase domain/activity edge of Itk.

Modeling susceptibility versus resistance in allergic airway disease reveals regulation by Tec kinase Itk

Murine models of allergic asthma have been used to understand the mechanisms of development and pathology in this disease. In addition, knockout mice have contributed significantly to our understanding of the roles of specific molecules and cytokines in these models. However, results can vary significantly depending on the mouse strain used in the model, and in particularly in understanding the effect of specific knockouts. For example, it can be equivocal as to whether specific gene knockouts affect the susceptibility of the mice to developing the disease, or lead to resistance. Here we used a house dust mite model of allergic airway inflammation to examine the response of two strains of mice (C57BL/6 and BALB/c) which differ in their responses in allergic airway inflammation. We demonstrate an algorithm that can facilitate the understanding of the behavior of these models with regards to susceptibility (to allergic airway inflammation) (S(aai)) or resistance (R(aai)) in this model. We verify that both C57BL/6 and BALB/c develop disease, but BALB/c mice have higher S(aai) for development. We then use this approach to show that the absence of the Tec family kinase Itk, which regulates the production of Th2 cytokines, leads to R(aai) in the C57BL/6 background, but decreases S(aai) on the BALB/c background. We suggest that the use of such approaches could clarify the behavior of various knockout mice in modeling allergic asthma.

Differential roles of IL-2-inducible T cell kinase-mediated TCR signals in tissue-specific localization and maintenance of skin intraepithelial T cells

Tissue-specific innate-like gammadelta T cells are important components of the immune system critical for the first line of defense, but mechanisms underlying their tissue-specific development are poorly understood. Our study with prototypical skin-specific intraepithelial gammadeltaT lymphocytes (sIELs) found that among different thymic gammadelta T cell subsets fetal thymic precursors of sIELs specifically acquire a unique skin-homing property after positive selection, suggesting an important role of the TCR selection signaling in "programming" them for tissue-specific development. In this study, we identified IL-2-inducible T cell kinase (ITK) as a critical signal molecule regulating the acquirement of the skin-homing property by the fetal thymic sIEL precursors. In ITK knockout mice, the sIEL precursors could not undergo positive selection-associated upregulation of thymus-exiting and skin-homing molecules sphingosine-1-phosphate receptor 1 and CCR10 and accumulated in the thymus. However, the survival and expansion of sIELs in the skin did not require ITK-transduced TCR signaling, whereas its persistent activation impaired sIEL development by inducing apoptosis. These findings provide insights into molecular mechanisms underlying differential requirements of TCR signaling in peripheral localization and maintenance of the tissue-specific T cells.

Combinatorial signals from CD28 differentially regulate human immunodeficiency virus transcription in T cells

Activation through the T-cell receptor and the costimulatory receptor CD28 supports efficient HIV transcription as well as reactivation of latent provirus. To characterize critical signals associated with CD28 that regulate HIV-1 transcription, we generated a library of chimeric CD28 receptors that harbored different combinations of key tyrosine residues in the cytoplasmic tail, Tyr-173, Tyr-188, Tyr-191, and Tyr-200. We found that Tyr-191 and Tyr-200 induce HIV-1 transcription via the activation of NF-kappaB and its recruitment to the HIV-long terminal repeat. Tyr-188 modifies positive and negative signals associated with CD28. Importantly, signaling through Tyr-188, Tyr-191, and Tyr-200 is required to overcome the inhibition posed by Tyr-173. CD28 also regulates P-TEFb activity, which is necessary for HIV-1 transcription processivity, by limiting the release of P-TEFb from the HEXIM1-7SK inhibitory complex in response to T-cell receptor signaling. Our studies reveal that CD28 regulates HIV-1 provirus transcription through a complex interplay of positive and negative signals that may be manipulated to control HIV-1 transcription and replication.

Aryl Hydrocarbon Receptor independent production of IL-17A in a murine model of Hypersensitivity Pneumonitis (87.12)

AhR (Aryl hydrocarbon Receptor) is a cytosolic transcription factor functioning as a sensor for environmental toxins. Recently, AhR has been suggested to have a cardinal role in Th17 biology. Although AhR is not a direct regulatory factor for Th17 differentiation its activation is required for the functional differentiation of Th17 cells, and production IL-22. To study the role of AhR in T cell differentiation we have used selective ligands of AhR in an in vitro assay and found that AhR agonist beta-naphthoflavone enhances IL-17 production whereas an AhR inhibitor suppresses it, both at the level of transcription and translation. The Th2 cytokine IL-4 was suppressed by beta-naphthoflavone and induced by the inhibitor and the Th1 cytokine IFNγ was inhibited by both the compounds. To further investigate the role of AhR in Th17 biology we used a well established Th17 dominated murine model of hypersensitivity pneumonitis mediated by a thermophilic actinomycete Staphylopolyspora rectivirgula (SR). Analysis of the cytokine transcripts from the SR exposed lungs revealed that IL-17 was not only expressed in WT mice but was more highly expressed in Ahr-null mice. These data suggest that the AhR may regulate cytokine production by other T cell subsets, and that the requirement for the AhR in IL-17 expression may be restricted to T cells. Further work is required to determine the role of the AhR in the innate immune cells, which are potential sources of IL-17.

Potent inhibition of calcium mobilization and mast cell activation by the pyrazole derivative BTP2 (86.9)

Cytosolic Ca2+ changes in mast cells are central for driving their activation. Thus, pharmacological tools that inhibit this process represent unique strategies for inhibiting mast cell function. We find that the pyrazole compound BTP2 inhibited FcϵRI-triggered sustained Ca2+ influx in a mast cell-like cell line RBL-2H3 with little effect on the tyrosine phosphorylation of cellular proteins. It also did not affect FcϵRI-induced phosphorylation of mitogen-activated protein kinases Erk1/2, JNK, and p38 nor downstream c-fos expression. This suggests that BTP2 inhibits Ca2+ mobilization without affecting the FcϵRI signal transduction cascade. BTP2 inhibited degranulation and β-hexosaminidase release in RBL-2H3 cells. Consistent with this effect, BTP2 inhibited antigen-induced histamine release in vivo. BTP2 also inhibited cytokine secretion of IL-2, IL-3, IL-4, IL-13, and TNF-α by BMMCs. Analysis of structure-function relationships between the BTP2 parent compound and its derivatives implicate a role for the trifluoromethyl group at both carbon positions 3 and 5 of pyrazole in the inhibition of degranulation of RBL-2H3 cells, with a more dominant effect evoked by the trifluoromethyl group at C3. In conclusion, our studies indicate that pyrazole compounds can provide the molecular framework for the design of specific inhibitors of Ca2+ entry mechanisms and further BTP2 as a medicinal candidate for the treatment of allergic reactions and other mast cell-mediated diseases.

Partial rescue of Itk-/- iNKT cell development by Txk/Rlk reveals a unique role for Itk in the survival of iNKT cells. (50.40)

Invariant natural killer T (iNKT) cells are a distinct population of innate T lymphocytes that play important role in the immune response. Itk and Txk/Rlk are Tec family kinases that are expressed in iNKT cells, with the expression level of Itk about 7-fold higher than that of Txk. It has been reported that the Itk null mice have reduced iNKT cell frequency and numbers, as well as defects in iNKT cell development and cytokine secretion, all of which are exacerbated in the Itk/Txk DKO mice. By contrast, the phenotype of iNKT cells in Txk null mice is similar to that from WT mice. In order to determine whether Itk and Txk plays distinct roles in iNKT cell development and function, we examined the iNKT cells in Tg(Lck-Txk)/Itk-/- mice, which over express Txk in T cells to the similar level as Itk. Over expression of Txk rescues the maturation and cytokine secretion of iNKT cells in Itk null mice. It also rescues the altered expression of transcription factor T-bet, eomesodermin and PLZF. By contrast, over expression of Txk does not rescue the reduced iNKT cell numbers in Itk null mice, which is due to the failure to rescue the increased apoptosis observed in Itk-/- iNKT cells. These data suggest that Txk plays an overlapping role with Itk in iNKT cell development and function, but that Itk also has a unique function in the survival of iNKT cells.