Allele-sensitive mutant, Itkas, reveals that Itk kinase activity is required for Th1, Th2, Th17, and iNKT-cell cytokine production

Itk(-/-) mice exhibit defects in the activation, development, and function of CD4(+) and CD8(+) T cells and iNKT cells. These and other defects in these mice make it difficult to uncouple the developmental versus functional requirement of Itk signaling. Here, we report an allele-sensitive mutant of Itk (Itkas) whose catalytic activity can be selectively inhibited by analogs of the PP1 kinase inhibitor. We show that Itkas behaves like WT Itk in the absence of the inhibitor and can rescue the development of Itk(-/-) T cells in mice. Using mice carrying Itkas, we show using its inhibitor that Itk activity is required not only for Th2, Th17, and iNKT-cell cytokine production, but also surprisingly, for Th1 cytokine production. This work has important implications for understanding the role of Itk signaling in the development versus function of iNKT cells, Th1, Th2, and Th17 cells.

Cutting Edge: Drebrin-Regulated Actin Dynamics Regulate IgE-Dependent Mast Cell Activation and Allergic Responses

Mast cells play critical roles in allergic responses. Calcium signaling controls the function of these cells, and a role for actin in regulating calcium influx into cells has been suggested. We have previously identified the actin reorganizing protein Drebrin as a target of the immunosuppressant 3,5-bistrifluoromethyl pyrazole, which inhibits calcium influx into cells. In this study, we show that Drebrin(-/-) mice exhibit reduced IgE-mediated histamine release and passive systemic anaphylaxis, and Drebrin(-/-) mast cells also exhibit defects in FcεRI-mediated degranulation. Drebrin(-/-) mast cells exhibit defects in actin cytoskeleton organization and calcium responses downstream of the FcεRI, and agents that relieve actin reorganization rescue mast cell FcεRI-induced degranulation. Our results indicate that Drebrin regulates the actin cytoskeleton and calcium responses in mast cells, thus regulating mast cell function in vivo.

Polymerase Mechanism-Based Method of Viral Attenuation

Vaccines remain the most effective way of preventing infection and spread of infectious diseases. These prophylactics have been used for centuries but still to this day only three main design strategies exist: (1) live attenuated virus (LAV) vaccines, (2) killed or inactivated virus vaccines, (3) and subunit vaccines of the three, the most efficacious vaccines remain LAVs. LAVs replicate in relevant tissues, elicit strong cellular and humoral responses, and often confer lifelong immunity. While this vaccine strategy has produced the majority of successful vaccines in use today, there are also important safety concerns to consider with this approach. In the past, the development of LAVs has been empirical. Blind passage of viruses in various cell types results in the accumulation of multiple attenuating mutations leaving the molecular mechanisms of attenuation unknown. Also, due to the high error rate of RNA viruses and selective pressures of the host environment, these LAVs, derived from such viruses, can potentially revert back to wild-type virulence. This not only puts the vaccinee at risk, but if shed can put those that are unvaccinated at risk as well. While these vaccines have been successful there still remains a need for a rational design strategy by which to create additional LAVs.One approach for rational vaccine design involves increasing the fidelity of the viral RdRp. Increased fidelity decreases the viral mutational frequency thereby reducing the genetic variation the virus needs in order to evade the host imposed bottlenecks to infection. While polymerase mutants exist which decrease viral mutation frequency the mutations are not in conserved regions of the polymerase, which doesn't lend itself toward using a common mutant approach toward developing a universal vaccine strategy for all RNA viruses. We have identified a conserved lysine residue in the active site of the PV RdRp that acts as a general acid during nucleotide incorporation. Mutation from a lysine to an arginine results in a high fidelity polymerase that replicates slowly thus creating an attenuated virus that is genetically stable and less likely to revert to a wild-type phenotype. This chapter provides detailed methods in which to identify the conserved lysine residue and evaluating fidelity and attenuation in cell culture (in vitro) and in the PV transgenic murine model (in vivo).

The microbiome regulates the eosinophil requirement for development of allergic lung inflammation (HYP2P.337)

The diversity of gastrointestinal and respiratory microflora is essential in the shaping the host immune responses. In particularly, the propensity for Th2 allergic responses and asthma has recently been linked to the dysbiosis of the gut microbiome. Thus, the early establishment of particular microflora may potentially explain why some individuals are more predisposed to develop asthma and some do not. Eosinophils may also make differential contributions to allergic asthma in different individuals, and we have previously shown that development of allergic asthma is dependent on eosinophils. Here we report that C57Bl/6 ΔdblGATA eosinophil deficient mice housed under “less-restricted specific-pathogen-free” (LR-SPF) conditions are protected against allergic asthma compared to mice house under “restricted specific-pathogen-free” (R-SPF) conditions. 16s rRNA analysis of gut and lung microbiome reveal differences in lung microbiota diversity, suggesting a potential explanation for this phenomenon. Furthermore, consistent with the “microbiota hypothesis”, reducing the microbiota in ΔdblGATA mice by antibiotic treatment resulted in enhanced susceptibility to developing allergic airway inflammation comparable to WT mice. Thus, we conclude that shifts in microbiota can affect the requirement for eosinophil-mediated Th2 responses.

ITK controls the functional stability of regulatory T cells by limiting pathogenic reprograming in inflamed mucosa (IRC11P.422)

CD25hiFoxp3+CD4+ regulatory T cells (Tregs) are important immune regulators that promote immune tolerance, but can also form barriers to effective immunity against tumor and chronic infection. IL-2-inducible T cell kinase (ITK) is highly expressed in T cells and regulates T cell development and function. We find that ITK is required for full suppressive function of natural Tregs in preventing the expansion of pro-inflammatory CD4+ effector T cells and chronic pulmonary and colonic inflammation upon transfer into Rag-/- mice. In the absence of ITK, Treg homing to these inflamed mucosal systems is intact, however, a significant proportion is converted into pathogenic effector T cells with ability to produce IL-17A and/or IFN-γ in the inflamed lung and colon, but not in the spleen. Such loss of functional stability and gain of pathogenic reprograming are T cell intrinsic and can be rescued by re-expression of ITK in Itk-/- Tregs. Homeostatic expansion contributed to the initiation of Itk-/- Treg destabilization and pathogenic conversion but did not trigger pathogenesis. Stimulation through the T cell receptor in the presence or absence of various cytokines revealed that ITK is required for sustaining Foxp3 expression. We conclude that ITK signals suppress pathogenic conversion of Tregs by maintaining Foxp3 expression, and contributes to the functional stability of Tregs in the face of inflammation by limiting their reprograming towards the pathogenic effectors.

The signaling symphony: T cell receptor tunes cytokine-mediated T cell differentiation

T cell development, differentiation, and maintenance are orchestrated by 2 key signaling axes: the antigen-specific TCR and cytokine-mediated signals. The TCR signals the recognition of self- and foreign antigens to control T cell homeostasis for immune tolerance and immunity, which is regulated by a variety of cytokines to determine T cell subset homeostasis and differentiation. TCR signaling can synergize with or antagonize cytokine-mediated signaling to fine tune T cell fate; however, the latter is less investigated. Murine models with attenuated TCR signaling strength have revealed that TCR signaling can function as regulatory feedback machinery for T cell homeostasis and differentiation in differential cytokine milieus, such as IL-2-mediated Treg development; IL-7-mediated, naïve CD8(+) T cell homeostasis; and IL-4-induced innate memory CD8(+) T cell development. In this review, we discuss the symphonic cross-talk between TCR and cytokine-mediated responses that differentially control T cell behavior, with a focus on the negative tuning by TCR activation on the cytokine effects.

Differential regulation of Th17 and T regulatory cell differentiation by aryl hydrocarbon receptor dependent xenobiotic response element dependent and independent pathways

The aryl hydrocarbon receptor (AHR) is regarded as an environmental sensor and has been shown to link environmental stresses with chronic inflammatory and autoimmune diseases. The AHR can be activated to regulate both the X/DRE (xenobiotic or dioxin response elements) as well as a non-X/DRE mediated pathway. Selective AHR modulators (SAhRMs) are recently identified compounds that activate non-X/DRE mediated pathway without activating the X/DRE-driven responses. Here, we have used 3 classes of AHR ligands; agonist, antagonist, and a SAhRM, to delineate the role of these AHR-driven pathways in T helper 17 (Th17)/T regulatory (Treg) regulation. We show that Th17 differentiation is primarily dependent on X/DRE-driven responses, whereas Treg differentiation can be suppressed by inhibiting non-X/DRE pathway. Using a model of Citrobacter rodentium infection, we further show that AHR agonist enhances Th17 production and promoted resolution of infection, whereas a SAhRM inhibited Th17 mediated responses with reduced resolution of infection. These data indicate that Th17/Treg function may be differentially regulated by SAhRMs that differentially activate the X/DRE and non-X/DRE mediated pathways, and point to a therapeutic strategy to leverage AHR function in the treatment of chronic inflammatory and autoimmune disease.

Cutting edge: STAT6 signaling in eosinophils is necessary for development of allergic airway inflammation

Eosinophils are critical cellular mediators in allergic asthma and inflammation; however, the signals that regulate their functions are unclear. The transcription factor STAT6 regulates Th2 cytokine responses, acting downstream of IL-4 and IL-13. We showed previously that eosinophil-derived IL-13 plays an important role in the recruitment of T cells to the lung and the subsequent development of allergic asthma. However, whether eosinophils respond to Th2 signals to control allergic airway inflammation is unclear. In this report, we show that STAT6(-/-) eosinophils are unable to induce the development of allergic lung inflammation, including recruitment of CD4(+) T cells, mucus production, and development of airways hyperresponsiveness. This is likely due to the reduced migration of STAT6(-/-) eosinophils to the lung and in response to eotaxin. These data indicate that, like Th cells, eosinophils need to respond to Th2 cytokines via STAT6 during the development of allergic airway inflammation.

People's instinctive travels and the paths to science

To be the recipient of the E. E. Just Award for 2014 is one of my greatest honors, as this is a truly rarefied group. In this essay, I try to trace my path to becoming a scientist to illustrate that multiple paths can lead to science. I also highlight that I did not build my career alone. Rather, I had help from many and have tried to pay it forward. Finally, as the country marches toward a minority majority, I echo the comments of previous E. E. Just Award recipients on the state of underrepresented minorities in science.

RNA virus population diversity, an optimum for maximal fitness and virulence

The ability of an RNA virus to exist as a population of genetically distinct variants permits the virus to overcome events during infections that would otherwise limit virus multiplication or drive the population to extinction. Viral genetic diversity is created by the ribonucleotide misincorporation frequency of the viral RNA-dependent RNA polymerase (RdRp). We have identified a poliovirus (PV) RdRp derivative (H273R) possessing a mutator phenotype. GMP misincorporation efficiency for H273R RdRp in vitro was increased by 2-3-fold that manifested in a 2-3-fold increase in the diversity of the H273R PV population in cells. Circular sequencing analysis indicated that some mutations were RdRp-independent. Consistent with the population genetics theory, H273R PV was driven to extinction more easily than WT in cell culture. Furthermore, we observed a substantial reduction in H273R PV virulence, measured as the ability to cause paralysis in the cPVR mouse model. Reduced virulence correlated with the inability of H273R PV to sustain replication in tissues/organs in which WT persists. Despite the attenuated phenotype, H273R PV was capable of replicating in mice to levels sufficient to induce a protective immune response, even when the infecting dose used was insufficient to elicit any visual signs of infection. We conclude that optimal RdRp fidelity is a virulence determinant that can be targeted for viral attenuation or antiviral therapies, and we suggest that the RdRp may not be the only source of mutations in a RNA virus genome.

MicroRNA-570-3p regulates HuR and cytokine expression in airway epithelial cells

Asthma is a chronic lung disease that affects people of all ages and is characterized by high morbidity. The mechanisms of asthma pathogenesis are unclear, and there is a need for development of diagnostic biomarkers and greater understanding of regulation of inflammatory responses in the lung. Post-transcriptional regulation of cytokines, chemokines, and growth factors by the action of microRNAs and RNA-binding proteins on stability or translation of mature transcripts is emerging as a central means of regulating the inflammatory response. In this study, we demonstrate that miR-570-3p expression is increased with TNFα stimuli in normal human bronchial epithelial cells (2.6 ± 0.6, p = 0.01) and the human airway epithelial cell line A549 (4.6 ± 1.4, p = 0.0068), and evaluate the functional effects of its overexpression on predicted mRNA target genes in transfected A549 cells. MiR-570-3p upregulated numerous cytokines and chemokines (CCL4, CCL5, TNFα, and IL-6) and also enhanced their induction by TNFα. For other cytokines (CCL2 and IL-8), the microRNA exhibited an inhibitory effect to repress their upregulation by TNFα. These effects were mediated by a complex pattern of both direct and indirect regulation of downstream targets by miR-570-3p. We also show that the RNA-binding protein HuR is a direct target of miR-570-3p, which has implications for expression of numerous other inflammatory mediators that HuR is known regulate post-transcriptionally. Finally, expression of endogenous miR-570-3p was examined in both serum and exhaled breath condensate (EBC) from asthmatic and healthy patients, and was found to be significantly lower in EBC of asthmatics and inversely correlated to their lung function. These studies implicate miR-570-3p as a potential regulator of asthmatic inflammation with potential as both a diagnostic and therapeutic target in asthma.

IL-2-inducible T cell kinase tunes T regulatory cell development and is required for suppressive function

IL-2-inducible T cell kinase (ITK) is a key signaling mediator downstream of TCR, mediating T cell positive selection, as well as innate T cell and CD4(+) Th2/Th17 differentiation. In this article, we show that ITK also negatively tunes IL-2-induced expansion of conventional Foxp3-expressing regulatory T cells (Tregs). In vivo, Treg abundance is inversely correlated with ITK expression, and inducible Treg development is inversely dependent on ITK kinase activity. While Treg development normally requires both hematopoietic and thymic MHC class 2 (MHC2) expression, the absence of ITK allows Treg development with MHC2 expression in either compartment, with preference for selection by thymic MHC2, suggesting a gatekeeper role for ITK in ensuring that only Tregs selected by both thymic and hematopoietic MHC2 survive selection. Although ITK suppresses Treg development and is not required for maintenance of neuropilin-1-positive natural Tregs in the periphery, it is indispensable for Treg functional suppression of naive CD4(+) T cell-induced colitis in Rag(-/-) recipients. ITK thus regulates the development and function of Tregs.

Signaling pathways in eosinophils that regulate allergic asthma and inflammation (HYP7P.304)

Allergic asthma and inflammation is a disease of the airways. The prevalence of allergic responses and asthma are increasing worldwide, but it is still unclear why some predisposed individuals develop disease. Eosinophils and T helper 2 cells (TH2) and eosinophils are critical cellular mediators in asthma. The signal transducer and activator of transcription (STAT)-6 is a crucial mediator of TH2 cytokine responses, acting downstream of interleukin -4 and -13 (IL-4 and IL-13). We have previously shown that eosinophil derived IL-13 plays an important role in the recruitment of T cells to the lung, and subsequent development of allergic asthma. However whether eosinophils respond to TH2 signals to control allergic airway inflammation is unclear. The objective of this study is to understand the role of STAT6 in eosinophil-dependent regulation of allergic asthma and inflammation. Using ΔdblGATA mice lacking eosinophils and transfer of STAT6-/- eosinophils, we found that compared to ΔdblGATA reconstituted with WT eosinophils, eosinophils lacking STAT6 were unable to rescue recruitment of CD4+ T cells and eosinophils into the lungs compared to WT eosinophils. These data indicates that STAT6 is important in the recruitment of both T cells and eosinophils to the lung during the development of allergic airway inflammation. Ultimately, deciphering the mechanisms of intracellular and cytokine signals will afford us improved insights on developing therapeutic strategies in asthma.

ITK signals tune CD8+ T cell homeostatic proliferation and anti-tumor immunity (LYM4P.747)

IL-2 inducible T cell kinase (ITK) is a Tec family non-receptor tyrosine kinase. Loss of ITK perturbs CD8+ T cell homeostasis and leads to spontaneous acquisition of innate memory/effector phenotype. However, Itk-/- naïve CD8+ T cells develop on an OTI Rag-/- background, and we use these cells to show here that ITK tunes lymphopenia-induced proliferation (LIP) and antigen sensitivity during CD8+ T cell homeostatic expansion. Experimental analysis and computational simulations revealed that in a lymphopenic environment, naïve Itk-/- CD8+ T cells exhibit massive and immediate homeostatic expansion, accompanied by significant death and followed by population collapse. The enhanced immediate expansion of Itk-/- cells is CD8+ T cell-intrinsic and is independent of recipient MHCI, but dependent on donor CD8+ T cell-T cell interaction. The lack of ITK resulted in enhanced antigen sensitivity and effector program in homeostatically expanded (HP) CD8+ T cells. These Itk-/- HP CD8+ T cells exhibit robust anti-tumor immunity in an antigen specific manner, independent of CD4+ T cell help. These data suggest that ITK intrinsically regulates TcR tuning of homeostatic cytokines during homeostasis of CD8+ T cells and that targeting ITK may have clinical benefit in cancer therapy by generating superior anti-tumor responses.

Dendritic cell-MHC class II and Itk regulate functional development of regulatory innate memory CD4+ T cells in bone marrow transplantation

MHC class II (MHCII)-influenced CD4(+) T cell differentiation and function play critical roles in regulating the development of autoimmunity. The lack of hematopoietic MHCII causes autoimmune disease that leads to severe wasting in syngeneic recipients. Using murine models of bone marrow transplantation (BMT), we find that MHCII(-/-)→wild-type BMT developed disease, with defective development of innate memory phenotype (IMP, CD44(hi)/CD62L(lo)) CD4(+) T cells. Whereas conventional regulatory T cells are unable to suppress pathogenesis, IMP CD4(+) T cells, which include conventional regulatory T cells, can suppress pathogenesis in MHCII(-/-)→wild-type chimeras. The functional development of IMP CD4(+) T cells requires hematopoietic but not thymic MHCII. B cells and hematopoietic CD80/86 regulate the population size, whereas MHCII expression by dendritic cells is sufficient for IMP CD4(+) T cell functional development and prevention of pathogenesis. Furthermore, the absence of Tec kinase IL-2-inducible T cell kinase in MHCII(-/-) donors leads to preferential development of IMP CD4(+) T cells and partially prevents pathogenesis. We conclude that dendritic cells-MHCII and IL-2-inducible T cell kinase regulate the functional development of IMP CD4(+) T cells, which suppresses the development of autoimmune disorder in syngeneic BMTs.

ITK tunes IL-4-induced development of innate memory CD8+ T cells in a γδ T and invariant NKT cell-independent manner

True memory CD8(+) T cells develop post antigenic exposure and can provide life-long immune protection. More recently, other types of memory CD8(+) T cells have been described, such as the memory-like CD8(+) T cells (IMP; CD44(hi)CD122(+)) that arise spontaneously in Itk(-/-) mice, which are suggested to develop as a result of IL-4 secreted by NKT-like γδ T or PLZF(+) NKT cells found in Itk(-/-) mice. However, we report here that whereas IMP CD8(+) T cell development in Itk(-/-) mice is dependent on IL-4/STAT6 signaling, it is not dependent on any γδ T or iNKT cells. Our experiments suggest that the IMP develops as a result of tuning of the CD8(+) T cell response to exogenous IL-4 and TCR triggering by ITK and challenge the current model of IMP CD8(+) T cell development as a result of NKT-like γδ T or iNKT cells. These findings suggest that some naive CD8(+) T cells may be preprogrammed by weak homeostatic TCR signals in the presence of IL-4 to become memory phenotype cells with the ability to elaborate effector function rapidly. The role of ITK in this process suggests a mechanism by which IMP CD8(+) T cells can be generated rapidly in response to infection.

Evaluation of the stability, bioavailability, and hypersensitivity of the omega-3 derived anti-leukemic prostaglandin: Δ(12)-prostaglandin J3

Previous studies have demonstrated the ability of an eicosapentaenoic acid (EPA)-derived endogenous cyclopentenone prostaglandin (CyPG) metabolite, Δ¹²-PGJ₃, to selectively target leukemic stem cells, but not the normal hematopoietic stems cells, in in vitro and in vivo models of chronic myelogenous leukemia (CML). Here we evaluated the stability, bioavailability, and hypersensitivity of Δ¹²-PGJ₃. The stability of Δ¹²-PGJ₃ was evaluated under simulated conditions using artificial gastric and intestinal juice. The bioavailability of Δ¹²-PGJ₃ in systemic circulation was demonstrated upon intraperitoneal injection into mice by LC-MS/MS. Δ¹²-PGJ₃ being a downstream metabolite of PGD₃ was tested in vitro using primary mouse bone marrow-derived mast cells (BMMCs) and in vivo mouse models for airway hypersensitivity. ZK118182, a synthetic PG analog with potent PGD₂ receptor (DP)-agonist activity and a drug candidate in current clinical trials, was used for toxicological comparison. Δ¹²-PGJ₃ was relatively more stable in simulated gastric juice than in simulated intestinal juice that followed first-order kinetics of degradation. Intraperitoneal injection into mice revealed that Δ¹²-PGJ₃ was bioavailable and well absorbed into systemic circulation with a C_max of 263 µg/L at 12 h. Treatment of BMMCs with ZK118182 for 12 h resulted in increased production of histamine, while Δ¹²-PGJ₃ did not induce degranulation in BMMCs nor increase histamine. In addition, in vivo testing for hypersensitivity in mice showed that ZK118182 induces higher airways hyperresponsiveness when compared Δ¹²-PGJ₃ and/or PBS control. Based on the stability studies, our data indicates that intraperitoneal route of administration of Δ¹²-PGJ₃ was favorable than oral administration to achieve effective pharmacological levels in the plasma against leukemia. Δ¹²-PGJ₃ failed to increase histamine and IL-4 in BMMCs, which is in agreement with reduced airway hyperresponsiveness in mice. In summary, our studies suggest Δ¹²-PGJ₃ to be a promising bioactive metabolite for further evaluation as a potential drug candidate for treating CML.

IL-2-inducible T-cell kinase modulates TH2-mediated allergic airway inflammation by suppressing IFN-γ in naive CD4+ T cells

BACKGROUND

Asthma is a predominantly TH2 cell-dominated inflammatory disease characterized by airway inflammation and a major public health concern affecting millions of persons. The Tec family tyrosine kinase IL-2-inducible T-cell kinase (Itk) is primarily expressed in T cells and critical for the function and differentiation of TH cells. Itk(-/-) mice have a defective TH2 response and are not susceptible to allergic asthma.

OBJECTIVE

We sought to better understand the role of Itk signaling in TH differentiation programs and in the development and molecular pathology of allergic asthma.

METHODS

Using a murine model of allergic airway inflammation, we dissected the role of Itk in regulating TH cell differentiation through genetic ablation of critical genes, chromatin immunoprecipitation assays, and house dust mite-driven allergic airway inflammation.

RESULTS

Peripheral naive Itk(-/-) CD4(+) T cells have substantially increased transcripts and expression of the prototypic TH1 genes Eomesodermin, IFN-γ, T-box transcription factor (T-bet), and IL-12Rβ1. Removal of IFN-γ on the Itk(-/-) background rescues expression of TH2-related genes in TH cells and allergic airway inflammation in Itk(-/-) mice. Furthermore, small hairpin RNA-mediated knockdown of Itk in human peripheral blood T cells results in increased expression of mRNA for IFN-γ and T-bet and reduction in expression of IL-4.

CONCLUSION

Our results indicate that Itk signals suppress the expression of IFN-γ in naive CD4(+) T cells, which in a positive feed-forward loop regulates the expression of TH1 factors, such as T-bet and Eomesodermin, and suppress development of TH2 cells and allergic airway inflammation.

ITK regulates the dynamics of CD8+ T cell homeostatic proliferation in lymphopenic environment (P1296)

Tec family kinase ITK is an essential regulator of T cell development and function. The absence of ITK leads to spontaneous acquisition of innate memory phenotype (IMP) in CD8+ T cells, shown to be induced by bystander-derived IL-4. CD8+ T cells undergone homeostatic proliferation (HP) in lymphopenic conditions share similar memory markers with IMP CD8+ T cells. To examine the role of ITK during CD8+ T cell HP, we compared naïve CD8+ T cells from WT and Itk-/- OTI-Rag-/- transgenic mice. We found that they had similar CD44loCD122- naïve phenotype, but naïve Itk-/- T cells exhibited increased Eomes, KLF2, FoxO3, Bim, Blimp-1 and decreased Bcl-6 mRNA expression. When transferred into lymphopenic Rag-/- recipients, Itk-/- naïve CD8+ T cells exhibited rapid early expansion, giving rise to > 10 fold expansion over that of WT CD8+ T cells by 10 days post-transfer, which was followed by massive retraction with failure to sustain a plateau as seen in WT. The absence of ITK during HP resulted in defects in expression of cytokine receptors and Bcl-2, accompanied by enhanced apoptosis and Fas expression. These data indicate an important role of ITK in regulating the dynamics and maintenance of CD8+ T cells during HP, likely by regulating the expression of cytokine receptors required for sustained survival of these cells. This work suggests that targeting the ITK pathway may allow manipulation of CD8+ T cell number and function in lymphopenic conditions due to infection or irradiation.

Role of Aryl hydrocarbon receptor and the effect of selective AhR modulators on T cell differentiation (P1201)

The physiological role of AhR, particularly in immune response remains a key question after identification of AhR as an essential transcription factor for Th17 differentiation. Selective AhR modulators (SAhRMs) are a recently identified class of compounds that are capable of binding to AhR and repress cytokine- driven gene expression. These compounds are interesting therapeutically as they can be used to inhibit Dioxin Response Element (DRE)-mediated while inducing anti-inflammatory responses. Under non-skewing conditions, AhR agonist beta-naphthoflavone (BNF) enhances IL-17A production whereas SGA-360 an inhibitor suppresses it. Under Th17 skewing condition, AhR agonist BNF enhanced Th17 differentiation whereas AhR antagonist GNF and partial antagonist SGA-360 suppressed it. Interestingly, under Treg skewing condition the antagonists enhanced the Foxp3 expression, suggesting that such compounds have therapeutic potential in autoimmune disease by modulating the Th17/Treg balance. We have also examined AhR antagonists after disease development in a murine model of Th17 mediated disease, hypersensitivity pneumonitis mediated by Staphylopolyspora rectivirgula (SR). We find that these antagonists suppress AhR activity and induce IL-4, suggestive of a shift in T helper lineage. This suggests that SAhRMs may be useful in modulating AhR activation to regulate Th17/Treg balance, and that AhR selective ligands have potential for use as therapeutics in Th17 mediated diseases.

Complex role for Interleukin-2 inducible T-cell kinase in T helper differentiation and effector function in vivo (P1204)

T helper responses are critical for a productive immune response but an inappropriate response results in inflammatory and autoimmune disorders. The tyrosine kinase ITK has been shown to regulate the development of Th2 responses. Here, we show that ITK regulates Th1/Th17 responses as well. We find that Itk-/- mice are more susceptible to infection by Th1 inducing intracellular pathogen T. gondii, with generation of fewer antigen specific Th1 cells in vivo and fewer effector cells ex vivo upon antigen re-challenge. Transfer of WT CD4+ T cells confers protection against infection in Itk-/- mice. Furthermore, WT but not Itk-/- CD4+ T cells can promote the survival of Rag-/- mice infected by T. gondii. Additionally, the absence of ITK is protective during Th1/Th17 mediated Experimental Autoimmune Encephalomyelitis (EAE) with fewer pathogenic Th1 and Th17 effector cells in the periphery. Furthermore, transfer of Itk-/- CD4+ T cells into Tcra-/- mice results in lower severity of EAE compared to mice that receive WT cells suggesting that Itk-/- CD4+ T cells are intrinsically less pathogenic. Finally, using mice that express an analog sensitive mutant of ITK (ITKas) we show that temporally inhibiting the kinase activity of ITK with a genetically selective small-molecule inhibitor impairs development of Th1, Th2, and Th17 lineages. This work has implications for understanding ITK as a therapeutic target for Th2 mediated inflammatory and Th1/Th17 mediated autoimmune disorders.

Cutting edge: innate memory CD8+ T cells are distinct from homeostatic expanded CD8+ T cells and rapidly respond to primary antigenic stimuli

Innate memory phenotype (IMP) CD8(+) T cells are nonconventional αβ T cells exhibiting features of innate immune cells and are significantly increased in the absence of ITK. Their developmental path and function are not clear. In this study, we show hematopoietic MHC class I (MHCI)-dependent generation of Ag-specific IMP CD8(+) T cells using bone marrow chimeras. Wild-type bone marrow gives rise to IMP CD8(+) T cells in MHCI(-/-) recipients, resembling those in Itk(-/-) mice, but distinct from those derived via homeostatic proliferation, and independent of recipient thymus. In contrast, MHCI(-/-) bone marrow does not lead to IMP CD8(+) T cells in wild-type recipients. OTI IMP CD8(+) T cells generated via this method exhibited enhanced early response to Ag without prior primary stimulation. Our findings suggest a method to generate Ag-specific "naive" CD8(+) IMP T cells, as well as demonstrate that they are not homeostatic proliferation cells and can respond promptly in an Ag-specific fashion.