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.

The Zinc binding site in the BH domain of Itk is required for interaction with Gα13 (50.10)

The Tec family kinase, Itk has been shown to be critical in T cell activation and development downstream of the T cell receptor (TCR). Migratory responses to chemokines such as CCL11/Eotaxin and CXCL12/SDF-1α require Itk. However, the mechanism by which chemokine receptor signals connect to Itk is not clear. We speculate Gα13 may serve to couple GPCRs, Itk and downstream signals. Using a Bimolecular Fluorescence Complementation system, we show that Itk and Gα13 are in close physical proximity, less than 80Å. This interaction requires the membrane localization of Itk, as the membrane targeting deficient mutants (S15P, R29C), lost their association with Gα13. Moreover, we found that mutations in the Zn2+ binding Bruton’s tyrosine kinase homology (BH) motif (C132GC133G), disrupted the interaction, even though this Itk mutant was still able to get recruited to membrane associated clusters. However, this interaction is Itk kinase activity independent. We also show that both GTP bound and GDP bound forms of Gα13 can interact with Itk. Surprisingly, co-expression of Itk and Gα13 resulted in tyrosine phosphorylation of Gα13. Taken together, we propose that interactions between Gα13 and Itk may connect chemokine/chemokine receptor stimulation and downstream responses regulated by Itk. Itk may also modulate the function of Gα13 by tyrosine phosphorylation. These data provide evidence for better understanding of the mechanism by which chemokines regulate immune cell responses.

Differential expression of IL-17A and IL-17F is coupled to TCR signaling via Itk-mediated regulation of NFATc1 (139.4)

Th17 CD4+ effector T cells play important roles in autoimmunity and responses to bacterial infections. The roles of cytokines in regulating the transcription factors STAT3 and RORγT in Th17 differentiation have been extensively studied. However, the role of T cell receptor (TCR) signaling in Th17 differentiation is less appreciated. To examine this issue, we evaluated IL17 production from T cells lacking Itk, a tyrosine kinase required for full TCR-induced activation of PLC-γ and downstream pathways. We find that Itk-/- CD4+T cells exhibit specific defects in the expression of IL-17A despite relatively normal expression of RORγT, RORα and the other Th17 cytokines, including the closely related IL-17F. Defects in IL-17A expression and differential regulation of IL-17A and IL-17F were also observed in vivo in Itk-/- mice challenged with an allergic asthma model. Although Itk-deficient cells have slightly depressed phosphorylation of STAT-3 in response to IL-6, expression of constitutively activated STAT-3 failed to rescue their IL-17A production. In contrast, expression of IL-17A could be rescued by pharmacologically-induced Ca2+ influx or by a constitutively active NFATc1. The effects of Itk on transcriptional complexes and chromatin at the IL-17 locus are under further investigation. Our results suggest that Itk specifically couples TCR signaling strength to IL-17A expression through NFATc1 and that TCR signaling pathways differentially influence Th17 cytokine production.

Absence of Tec family kinases Itk and Btk significantly impairs FcϵRI dependent mast cell responses (86.26)

While the etiology of asthma can be multi factorial, signaling through the IgE receptor (Fcϵ receptor I) on mast cells is critical to its onset. The Tec family tyrosine kinases ITK and BTK serve important roles as signal amplifiers downstream of the FcϵRI, however, their individual contribution to FcϵRI signaling has not been fully established. We have generated Itk and Btk double deficient (DKO) mice in an effort to determine the relative role of Itk and Btk to FcϵRI signaling in mast cells. Analyses of skin mast cells from these mice revealed reduced mast cell granule content and density. However, in vitro cultured bone marrow derived mast cells (BMMCs) had normal gross morphology and granule density. Mast cell histamine release was also compromised in DKO mice, likely associated with elevated endogenous IgE expression in these mice. In vitro growth analysis indicated that Btk negatively regulates BMMC growth as previously published, while the absence of both Itk/Btk did not further contribute to this phenotype. However, there was a significant reduction in FcϵRI mediated calcium responses, accompanied by reduced phosphorylation of PLCγ2 and the mitogen activated protein kinase p38. Lastly, a reduction in the production of several cytokines was also observed in DKO BMMCs. Our results suggest that Itk and Btk have redundant, complementary, and unique functions in mast cell FcϵRI signaling that could be pharmacologically manipulated to treat asthma.

The role of eosinophils in allergic airway inflammation

Eosinophils have long been observed in the airways of patients with allergic asthma, and in animal models of allergic airway inflammation. Traditionally thought to be an end stage cell that is controlled by the T cell response, more recent findings suggest a more complicated role for these cells. Here we discuss the role of eosinophils in allergic inflammation, and recent findings that suggest an important role in the initiation of allergic airway inflammation. Finally, we discuss some ways in which these cells are being targeted in patients, and promising preclinical findings on novel targets for decreasing the number of these cells in patients with allergic asthma.

p38 MAP kinase is necessary for melanoma-mediated regulation of VE-cadherin disassembly

Vascular endothelial (VE)-cadherin is localized to the endothelial borders and the adherens junctions, which are regulated by changes in mitogen-activated protein (MAP) kinases, GTPases, and intracellular calcium. We previously showed that melanoma cells induce VE-cadherin disassembly through contact with human umbilical vein endothelial cells in coculture. However, the exact mechanism by which melanoma cells signal endothelial cells to induce VE-cadherin junction disassembly is not well understood. In this study, VE-cadherin junction disassembly was further examined under fluorescence microscopy. We found that melanoma-induced VE-cadherin junction disassembly and upregulation of p38 MAP kinase in endothelial cells is regulated by both soluble factors from melanomas, particularly interleukin (IL)-8, IL-6, and IL-1beta, and through vascular cell adhesion molecule-1. Neutralizing melanoma-secreted soluble factors reduced endothelial gap formation. Endothelial cells transfected with MAP kinase kinase 6, a direct activator of p38 MAP kinase, increased VE-cadherin-mediated gap formation, facilitating melanoma transendothelial migration. In contrast, endothelial cells transfected with small-interfering RNA against p38 MAP kinase expression largely prevented melanoma transendothelial migration in Boyden chamber experiments. These findings indicate that p38 MAP kinase proteins regulate VE-cadherin junction disassembly, facilitating melanoma migration across endothelial cells.

Itk derived signals regulate the expression of Th-POK and controls the development of CD4 T cells

T cell development is critically dependent on both the environment and signals delivered by the T cell Receptor (TCR). The Tec family kinase Itk has been suggested to be an amplifier of signals emanating from the TCR and the loss of Itk partially affects most stages of thymopoiesis. Loss of Itk also differentially affects the development of conventional vs. non-conventional or innate memory phenotype T cells. Here, we examine whether these lineage choices are affected by a combination of TCR affinity and Itk by analyzing mice lacking Itk and carrying two TCR transgenes with differing affinities, OT-II and DO11.10. Our results show that developing thymocytes receive a gradient of signals, DO11.10>OT-II>DO11.10/Itk(-/-)>OT-II/Itk(-/-). We also show that the development of CD4(+) T cells is controlled by TCR signaling via Itk, which regulates the expression of the transcription factor, Th-POK, an enforcement factor for CD4 commitment. This results in a reduction in CD4(+) T cell development, and an increase in the development of MHC class II restricted TCR transgenic CD8(+) T cells that resemble non-conventional or innate memory phenotype CD8 T cells. This alteration accompanies increased expression of Runx3 and its target genes Eomesodermin, Granzyme B and Perforin in Itk null OT-II CD4(+) thymocytes. All together, these data suggest that Itk plays an important role in CD4/CD8 commitment by regulating signal thresholds for the lineage commitment. Our data also suggest that the lower level of TCR signaling that occurs with a low affinity TCR in the absence of Itk can redirect some MHC class II restricted CD4(+) T cell to class II-restricted CD8(+) innate memory phenotype T cells.

Chemico-genetic identification of drebrin as a regulator of calcium responses

Store-operated calcium channels are plasma membrane Ca(2+) channels that are activated by depletion of intracellular Ca(2+) stores, resulting in an increase in intracellular Ca(2+) concentration, which is maintained for prolonged periods in some cell types. Increases in intracellular Ca(2+) concentration serve as signals that activate a number of cellular processes, however, little is known about the regulation of these channels. We have characterized the immuno-suppressant compound BTP, which blocks store-operated channel mediated calcium influx into cells. Using an affinity purification scheme to identify potential targets of BTP, we identified the actin reorganizing protein, drebrin, and demonstrated that loss of drebrin protein expression prevents store-operated channel mediated Ca(2+) entry, similar to BTP treatment. BTP also blocks actin rearrangements induced by drebrin. While actin cytoskeletal reorganization has been implicated in store-operated calcium channel regulation, little is known about actin-binding proteins that are involved in this process, or how actin regulates channel function. The identification of drebrin as a mediator of this process should provide new insight into the interaction between actin rearrangement and store-operated channel mediated calcium influx.

Eosinophils and allergic airway disease: there is more to the story

The eosinophil has been perceived as a terminal effector cell in allergic airway diseases. However, recent work has shown that this multifunctional cell could be more involved in the initial stages of allergic disease development than was previously thought, particularly with regard to the ability of the eosinophil to modulate T-cell responses. In this review, we discuss recent advances that suggest that eosinophils can present antigen to naïve as well as to antigen-experienced T cells, induce T helper 2 cell development, cytokine production or both, and affect T-cell migration to sites of inflammation. These findings are changing the way that eosinophil function in disease is perceived, and represent a shift in the dogma of allergic disease development.

ITK inhibitors in inflammation and immune-mediated disorders

Interleukin-2-inducible T cell kinase (ITK) is a non-receptor tyrosine kinase expressed in T cells, NKT cells and mast cells which plays a crucial role in regulating the T cell receptor (TCR), CD28, CD2, chemokine receptor CXCR4, and FcepsilonR-mediated signaling pathways. In T cells, ITK is an important mediator for actin reorganization, activation of PLCgamma, mobilization of calcium, and activation of the NFAT transcription factor. ITK plays an important role in the secretion of IL-2, but more critically, also has a pivotal role in the secretion of Th2 cytokines, IL-4, IL-5 and IL-13. As such, ITK has been shown to regulate the development of effective Th2 response during allergic asthma as well as infections of parasitic worms. This ability of ITK to regulate Th2 responses, along with its pattern of expression, has led to the proposal that it would represent an excellent target for Th2-mediated inflammation. We discuss here the possibilities and pitfalls of targeting ITK for inflammatory disorders.

Differential expression of interleukin-17A and -17F is coupled to T cell receptor signaling via inducible T cell kinase

T helper 17 (Th17) cells play major roles in autoimmunity and bacterial infections, yet how T cell receptor (TCR) signaling affects Th17 cell differentiation is relatively unknown. We demonstrate that CD4(+) T cells lacking Itk, a tyrosine kinase required for full TCR-induced phospholipase C-gamma (PLC-gamma1) activation, exhibit decreased interleukin-17A (IL-17A) expression in vitro and in vivo, despite relatively normal expression of retinoic acid receptor-related orphan receptor-gammaT (ROR-gammaT) and IL-17F. IL-17A expression was rescued by pharmacologically induced Ca(2+) influx or constitutively activated nuclear factor of activated T cells (NFAT). Conversely, decreased TCR stimulation or calcineurin inhibition preferentially reduced IL-17A expression. We further found that the promoter of Il17a but not Il17f has a conserved NFAT binding site that bound NFATc1 in wild-type but not Itk-deficient cells, even though both exhibited open chromatin conformations. Finally, Itk(-/-) mice also showed differential regulation of IL-17A and IL-17F in vivo. Our results suggest that Itk specifically couples TCR signaling to Il17a expression and the differential regulation of Th17 cell cytokines through NFATc1.

IL-2-inducible T-cell kinase (ITK) finds another (dance) partner...TFII-I

The signals that regulate T-cell activation have been studied for some time. We know that upon interaction with antigen/MHC complex, the TCR triggers the activation of a number of kinases, including tyrosine and serine/threonine kinases. The Tec family kinase IL-2- inducible T-cell kinase (ITK) plays a role in this response, but the signaling pathways that ITK regulates are less well known. Even less known are the binding partners and substrates of ITK. A paper in this issue of the European Journal of Immunology extends our knowledge on the subject by showing that ITK interacts with the transcriptional regulator TFII-I. The implications of this finding are discussed.

The Tec family kinase Itk exists as a folded monomer in vivo

Tec family tyrosine kinases transduce signals from antigen and other receptors. In particular, Itk plays an important role in T-cell development and activation. Itk has an N-terminal pleckstrin homology domain, a Tec Homology domain with a proline-rich region, SH3 and SH2 domains and a kinase domain, the structure each of which has been determined. However, the full structure of Itk and other Tec kinases remain elusive. Models of Itk suggest either a head to tail dimer, with the SH2 domain interacting with the SH3 domain, or a folded monomer with the SH3 domain interacting with the proline-rich region. We show here that in vivo Itk exists as a monomer, with the pleckstrin homology domain less than 80 A from the C terminus. Zn2+ coordinating residues in the Tec Homology domain, not the proline-rich region, are critical for this intramolecular interaction. These data have implications for our understanding of Tec family kinase structure.

Expression of a phosphorylated p130(Cas) substrate domain attenuates the phosphatidylinositol 3-kinase/Akt survival pathway in tamoxifen resistant breast cancer cells

Elevated expression of p130(Cas)/BCAR1 (breast cancer anti estrogen resistance 1) in human breast tumors is a marker of poor prognosis and poor overall survival. Specifically, p130(Cas) signaling has been associated with antiestrogen resistance, for which the mechanism is currently unknown. TAM-R cells, which were established by long-term exposure of estrogen (E(2))-dependent MCF-7 cells to tamoxifen, displayed elevated levels of total and activated p130(Cas). Here we have investigated the effects of p130(Cas) inhibition on growth factor signaling in tamoxifen resistance. To inhibit p130(Cas), a phosphorylated substrate domain of p130(Cas), that acts as a dominant-negative (DN) p130(Cas) molecule by blocking signal transduction downstream of the p130(Cas) substrate domain, as well as knockdown by siRNA was employed. Interference with p130(Cas) signaling/expression induced morphological changes, which were consistent with a more epithelial-like phenotype. The phenotypic reversion was accompanied by reduced migration, attenuation of the ERK and phosphatidylinositol 3-kinase/Akt pathways, and induction of apoptosis. Apoptosis was accompanied by downregulation of the expression of the anti-apoptotic protein Bcl-2. Importantly, these changes re-sensitized TAM-R cells to tamoxifen treatment by inducing cell death. Therefore, our findings suggest that targeting the product of the BCAR1 gene by a peptide which mimics the phosphorylated substrate domain may provide a new molecular avenue for treatment of antiestrogen resistant breast cancers.

The Birmingham Hip Resurfacing: 5-year clinical and radiographic results from a District General Hospital

We prospectively examined the functional and radiographic outcomes of a serial cohort of 104 Birmingham Hip Resurfacings in an independent centre. Final follow-up was to a mean of 61 months, and six cases were lost to follow-up. Excellent results were obtained in 91%, but obese patients had significantly (p < 0.03) poorer post-operative outcomes. Whilst there were no cases of neck fracture neck narrowing of up to 20 mm was noted. Radiolucent lines were present in a single zone in 9.4% (9/96) acetabular and 3.1% (3/96) femoral components. However, no components were definitely loose and there were no revisions for any reason during the period of the study. This independent series confirms that the Birmingham Hip Resurfacing gives excellent early clinical results and little early evidence of radiographic failure. The high rate of neck narrowing gives us cause for concern and we would recommend regular radiographic follow-up.

Tec family non-receptor tyrosine kinase ITK is important for the development of skin-specific intraepithelial T cells through regulation of their skin-homing property (96.17)

Proper localization of immune cells during the development is critical for their optimal functions. Murine skin-specific intraepithelial T cells (sIELs) are a unique tissue-specific innate T cell population that function in the first line of defense to maintain the local tissue integrity. The sIELs originate from their fetal thymic progenitors that specifically express canonical Vγ3+ TCR. Although it has been shown that the expression of skin-homing molecules, such as CCR10, is associated with the TCR-mediated cellular selection of the progenitors for their development into sIELs, molecules that mediate the selection-associated homing molecule expression is not fully understood. Here we report that ITK-null mice have a defective sIEL development due to impaired expression of the homing molecules in the fetal thymic sIEL progenitors. In the absence of ITK, the fetal thymic Vγ3+ cells failed to upregulate the expression of the chemokine receptors important for their thymus-exiting and skin-homing, including S1P1 and CCR10, which was associated with a gradient accumulation of the Vγ3 cells in the fetal thymus and a severe defect in their seeding of the skin. On the other hand, the ITK deficiency did not affect the TCR- or IL-15 receptor-mediated proliferation of the progenitor cells. These results indicate that ITK-mediated signaling is critical for the acquirement of proper homing property by the sIEL progenitors for their peripheral localization.

Selective expression rather than specific function of Txk and Itk regulate Th1 and Th2 responses

Itk and Txk/Rlk are Tec family kinases expressed in T cells. Itk is expressed in both Th1 and Th2 cells. By contrast, Txk is preferentially expressed in Th1 cells. Although Itk is required for Th2 responses in vivo and Txk is suggested to regulate IFN-gamma expression and Th1 responses, it remains unclear whether these kinases have distinct roles in Th cell differentiation/function. We demonstrate here that Txk-null CD4(+) T cells are capable of producing both Th1 and Th2 cytokines similar to those produced by wild-type CD4(+) T cells. To further examine whether Itk and Txk play distinct roles in Th cell differentiation and function, we examined Itk-null mice carrying a transgene that expresses Txk at levels similar to the expression of Itk in Th2 cells. Using two Th2 model systems, allergic asthma and schistosome egg-induced lung granulomas, we found that the Txk transgene rescued Th2 cytokine production and all Th2 symptoms without notable enhancement of IFN-gamma expression. These results suggest that Txk is not a specific regulator of Th1 responses. Importantly, they suggest that Itk and Txk exert their effects on Th cell differentiation/function at the level of expression.

Elevated non-specific immunity and normal Listeria clearance in young and old vitamin D receptor knockout mice

1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] and the vitamin D receptor (VDR) are important regulators of autoimmunity. The effect of the VDR on the ability of mice to fight a primary or secondary infection has not been determined. Young and old VDR knockout (KO) mice were able to clear both primary and secondary infections with Listeria monocytogenes. However, the kinetics of clearance was somewhat delayed in the absence of the VDR. Memory T cell development was not different in young VDR KO and wild-type (WT) mice; however, old VDR KO mice had significantly less memory T cells than their WT counterparts but still mounted an adequate immune response as determined by the complete clearance of L. monocytogenes. Although the primary and secondary immune responses were largely intact in the VDR KO mice, the old VDR KO mice had increased cytokines and antibody responses compared with the old WT mice. In particular, old VDR KO mice had elevated antigen non-specific antibodies; however, these magnified immune responses did not correspond to more effective Listeria clearance. The increased antibody and cytokine responses in the old VDR KO mice are consistent with the increased susceptibility of these mice to autoimmunity.

The Src kinase Lck facilitates assembly of HIV-1 at the plasma membrane

HIV type 1 (HIV-1) assembly and egress are driven by the viral protein Gag and occur at the plasma membrane in T cells. Recent evidence indicates that secretory vesicles and machinery are essential components of virus packaging in both T cells and macrophages. However, the pathways and cellular mediators of Gag targeting to the plasma membrane are not well characterized. Lck, a lymphoid specific Src kinase critical for T cell activation, is found in the plasma membrane as well as various intracellular compartments and it has been suggested to influence HIV-1 replication. To investigate Lck as a potential regulator of Gag targeting, we assessed HIV-1 replication and Gag-induced virus-like particle release in the presence and absence of Lck. Release of HIV-1 and virus-like particles was reduced in the absence of Lck. This decrease in replication was not due to altered HIV-1 infection, transcription or protein translation. However, in T cells lacking Lck, HIV-1 accumulated intracellularly. In addition, expressing Lck in HeLa cells promoted HIV-1 Gag plasma membrane localization. Palmitoylation of the Lck unique domain, which is essential for directing Lck to the plasma membrane, was critical for its effect on HIV-1 replication. Furthermore, HIV-1 Gag directly interacted with the Lck unique domain in the context of infected cells. These results indicate that Lck plays a key role in targeting HIV-1 Gag to the plasma membrane in T cells.

The Tec family kinase, IL-2-inducible T cell kinase, differentially controls mast cell responses

The Tec family tyrosine kinase, IL-2-inducible T cell kinase (Itk), is expressed in T cells and mast cells. Mice lacking Itk exhibit impaired Th2 cytokine secretion; however, they have increased circulating serum IgE, but exhibit few immunological symptoms of allergic airway responses. We have examined the role of Itk in mast cell function and FcepsilonRI signaling. We report in this study that Itk null mice have reduced allergen/IgE-induced histamine release, as well as early airway hyperresponsiveness in vivo. This is due to the increased levels of IgE in the serum of these mice, because the transfer of Itk null bone marrow-derived cultured mast cells into mast cell-deficient W/W(v) animals is able to fully rescue histamine release in the W/W(v) mice. Further analysis of Itk null bone marrow-derived cultured mast cells in vitro revealed that whereas they have normal degranulation responses, they secrete elevated levels of cytokines, including IL-13 and TNF-alpha, particularly in response to unliganded IgE. Analysis of biochemical events downstream of the FcepsilonRI revealed little difference in overall tyrosine phosphorylation of specific substrates or calcium responses; however, these cells express elevated levels of NFAT, which was largely nuclear. Our results suggest that the reduced mast cell response in vivo in Itk null mice is due to elevated levels of IgE in these mice. Our results also suggest that Itk differentially modulates mast cell degranulation and cytokine production in part by regulating expression and activation of NFAT proteins in these cells.

Naive and innate memory phenotype CD4+ T cells have different requirements for active Itk for their development

The Tec family kinase Itk regulates the development of conventional and innate CD8(+) T cells. However, little is known about the role of Itk in the development of CD4(+) T cell lineages, although the role of Itk in the T cell activation and function is well defined. We show in this study that Itk null mice have increased percentage of CD62L(low)CD44(high) memory phenotype CD4(+) T cells compared with wild-type mice. These cells arise directly in the thymus, express high levels of transcripts for the T-bet and IFN-gamma and are able to produce IFN-gamma directly ex vivo in response to stimulation. Itk deficiency greatly decreases the number of CD4(+) T cells with CD62L(high)CD44(low) naive phenotype, but has no effect on the number of memory phenotype CD4(+) T cells, indicating that the development of memory phenotype CD4(+) T cells is Itk-independent. We further show that the development of the naive phenotype CD4(+) T cells is dependent on active Itk signals and can be rescued by expression of Itk specifically in T cells. Our data also show that Itk is required for functional TCR signaling in these cells, but not for the innate function in response to IL-12/IL-18 or Listeria monocytogenes stimulation. These results indicate that CD62L(high)CD44(low) "naive" CD4(+) and CD62L(low)CD44(high) "innate memory phenotype" CD4(+) T cells may be independent populations that differ in their requirement for Itk signals for development. Our data also suggest that CD4(+)CD62L(low)CD44(high) memory phenotype T cells have innate immune function.

Differential sensitivity to Itk kinase signals for T helper 2 cytokine production and chemokine-mediated migration

Allergic asthma is dependent on chemokine-mediated Th2 cell migration and Th2 cytokine secretion into the lungs. The inducible T cell tyrosine kinase Itk regulates the production of Th2 cytokines as well as migration in response to chemokine gradients. Mice lacking Itk are resistant to developing allergic asthma. However, the role of kinase activity of Itk in the development of this disease is unclear. In addition, whether distinct Itk-derived signals lead to T cell migration and secretion of Th2 cytokines is also unknown. Using transgenic mice specifically lacking Itk kinase activity, we show that active kinase signaling is required for control of Th2 responses and development of allergic asthma. Moreover, dominant suppression of kinase Itk activity led to normal Th2 responses, but significantly reduced chemokine-mediated migration, resulting in prevention of allergic asthma. These observations indicate that signals required for Th2 responses and migration are differentially sensitive to Itk activity. Manipulation of Itk's activity can thus provide a new strategy to treat allergic asthma by differentially affecting migration of T cells into the lungs, leaving Th2 responses intact.

Strain-specific requirement for eosinophils in the recruitment of T cells to the lung during the development of allergic asthma

Eosinophils have been implicated as playing a major role in allergic airway responses. However, the importance of these cells to the development of this disease has remained ambiguous despite many studies, partly because of lack of appropriate model systems. In this study, using transgenic murine models, we more clearly delineate a role for eosinophils in asthma. We report that, in contrast to results obtained on a BALB/c background, eosinophil-deficient C57BL/6 ΔdblGATA mice (eosinophil-null mice via the ΔDblGATA1 mutation) have reduced airway hyperresponsiveness, and cytokine production of interleukin (IL)-4, -5, and -13 in ovalbumin-induced allergic airway inflammation. This was caused by reduced T cell recruitment into the lung, as these mouse lungs had reduced expression of CCL7/MCP-3, CC11/eotaxin-1, and CCL24/eotaxin-2. Transferring eosinophils into these eosinophil-deficient mice and, more importantly, delivery of CCL11/eotaxin-1 into the lung during the development of this disease rescued lung T cell infiltration and airway inflammation when delivered together with allergen. These studies indicate that on the C57BL/6 background, eosinophils are integral to the development of airway allergic responses by modulating chemokine and/or cytokine production in the lung, leading to T cell recruitment.