Makio Iwashima

ZAP-70: A 70 kd protein-tyrosine kinase that associates with the TCR ζ chain

Abstract Protein-tyrosine kinases (PTKs) play an integral role in T cell activation. Stimulation of the T cell antigen receptor (TCR) results in tyrosine phosphorylation of a number of cellular substrates. One of these is the TCR ζ chain, which can mediate the transduction of extracellular stimuli into cellular effector functions. We have recently identified a 70 kd tyrosine phosphoprotein (ZAP-70) that associates with ζ and undergoes tyrosine phosphorylation following TCR stimulation. Here we report the isolation of a cDNA clone encoding ZAP-70. ZAP-70 represents a novel PTK and is expressed in T and natural killer cells. Moreover, tyrosine phosphorylation and association of ZAP-70 with ζ require the presence of src family PTKs and provide a potential mechanism by which the src family PTKs and ZAP-70 may interact to mediate TCR signal transduction.

Cutting Edge: Induced Indoleamine 2,3 Dioxygenase Expression in Dendritic Cell Subsets Suppresses T Cell Clonal Expansion

In mice, immunoregulatory APCs express the dendritic cell (DC) marker CD11c, and one or more distinctive markers (CD8α, B220, DX5). In this study, we show that expression of the tryptophan-degrading enzyme indoleamine 2,3 dioxygenase (IDO) is selectively induced in specific splenic DC subsets when mice were exposed to the synthetic immunomodulatory reagent CTLA4-Ig. CTLA4-Ig did not induce IDO expression in macrophages or lymphoid cells. Induction of IDO completely blocked clonal expansion of T cells from TCR transgenic mice following adoptive transfer, whereas CTLA4-Ig treatment did not block T cell clonal expansion in IDO-deficient recipients. Thus, IDO expression is an inducible feature of specific subsets of DCs, and provides a potential mechanistic explanation for their T cell regulatory properties.

IL-2 is a critical regulator of group 2 innate lymphoid cell function during pulmonary inflammation

BACKGROUND Group 2 innate lymphoid cells (ILC2) have been implicated in the pathogenesis of allergic lung diseases. However, the upstream signals that regulate ILC2 function during pulmonary inflammation remain poorly understood. ILC2s have been shown to respond to exogenous IL-2, but the importance of endogenous IL-2 in ILC2 function in vivo remains unclear. OBJECTIVE We sought to understand the role of IL-2 in the regulation of ILC2 function in the lung. METHODS We used histology, flow cytometry, immunohistochemistry, ELISA, and quantitative PCR with knockout and reporter mice to dissect pulmonary ILC2 function in vivo. We examined the role of ILC2s in eosinophilic crystalline pneumonia, an idiopathic type 2 inflammatory lung condition of mice, and the effect of IL-2 deficiency on this disease. We determined the effect of IL-2 administration on pulmonary ILC2 numbers and function in mice in the steady state and after challenge with IL-33. RESULTS We discovered an unexpected role for innate cell-derived IL-2 as a major cofactor of ILC2 function during pulmonary inflammation. Specifically, we found that IL-2 was essential for the development of eosinophilic crystalline pneumonia, a type 2 disease characterized by increased numbers of activated ILC2s. We show that IL-2 signaling serves 2 distinct functions in lung ILC2s, namely promoting cell survival/proliferation and serving as a cofactor for the production of type 2 cytokines. We further demonstrate that group 3 innate lymphoid cells are an innate immune source of IL-2 in the lung. CONCLUSION Innate cell-derived IL-2 is a critical cofactor in regulating ILC2 function in pulmonary type 2 pathology.

The kinase, SH3, and SH2 domains of Lck play critical roles in T-cell activation after ZAP-70 membrane localization.

Antigenic stimulation of the T-cell antigen receptor initiates signal transduction through the immunoreceptor tyrosine-based activation motifs (ITAMs). When its two tyrosines are phosphorylated, ITAM forms a binding site for ZAP-70, one of the cytoplasmic protein tyrosine kinases essential for T-cell activation. The signaling process that follows ZAP-70 binding to ITAM has been analyzed by the construction of fusion proteins that localize ZAP-70 to the plasma membrane. We found that membrane-localized forms of ZAP-70 induce late signaling events such as activation of nuclear factor of activated T cells without any stimulation. This activity was observed only when Lck was expressed and functional. In addition, each mutation that affects the function of Lck in the kinase, Src homology 2 (SH2), and SH3 domains greatly impaired the signaling ability of the chimeric protein. Therefore, Lck functions in multiple manners in T-cell activation for the steps following ZAP-70 binding to ITAM.

Kinetic perspectives of T cell antigen receptor signaling

T‐cell activation consists of multiple layers of signaling events. Interleukin‐2 production is of interest for many, since its expression determines a critical difference between partial and full T‐cell activation. To achieve full activation of T cells, it is necessary for the T‐cell antigen receptor (TCR) to be engaged for an extended period of time. However, why extended stimulation is required for full T‐cell activation is not understood at the molecular level. In this review, orchestrated events of TCR signal transduction will be analyzed in a kinetic manner and connected toward the understanding of the mechanism of T‐cell activation. Based on recent results, a model of the mechanism that dictates the threshold between partial and full T‐cell activation is proposed.

Cellular Basis of Tissue Regeneration by Omentum

The omentum is a sheet-like tissue attached to the greater curvature of the stomach and contains secondary lymphoid organs called milky spots. The omentum has been used for its healing potential for over 100 years by transposing the omental pedicle to injured organs (omental transposition), but the mechanism by which omentum helps the healing process of damaged tissues is not well understood. Omental transposition promotes expansion of pancreatic islets, hepatocytes, embryonic kidney, and neurons. Omental cells (OCs) can be activated by foreign bodies in vivo. Once activated, they become a rich source for growth factors and express pluripotent stem cell markers. Moreover, OCs become engrafted in injured tissues suggesting that they might function as stem cells. Omentum consists of a variety of phenotypically and functionally distinctive cells. To understand the mechanism of tissue repair support by the omentum in more detail, we analyzed the cell subsets derived from the omentum on immune and inflammatory responses. Our data demonstrate that the omentum contains at least two groups of cells that support tissue repair, immunomodulatory myeloid derived suppressor cells and omnipotent stem cells that are indistinguishable from mesenchymal stem cells. Based on these data, we propose that the omentum is a designated organ for tissue repair and healing in response to foreign invasion and tissue damage.

Genetic evidence for Shc requirement in TCR-induced c-Rel nuclear translocation and IL-2 expression

Shc, a prototypic adapter molecule, has been implicated in T cell receptor (TCR) signal transduction, but its role has not been identified clearly. Here we report that Shc is essential for TCR-induced IL-2 production but is dispensable for CD69 or CD25 expression. Engagement of TCR in mutant Jurkat T cells lacking Shc fails to produce IL-2 because of impaired mitogen-activated protein kinase activation. Activation of c-Rel, a transcription factor essential for IL-2 expression, was impaired also. In contrast, activation of nuclear factor of activated T cell and expression of CD69/CD25 were comparable between the mutant and wild-type Jurkat cells. These defects were rescued by expression of exogenous Shc. Activation of c-Rel using the estrogen receptor fusion protein restored the activation of the IL-2 promoter in an estrogen-dependent manner. These results show that Shc plays an essential role in the TCR-induced activation of c-Rel and the IL-2 promoter.

CD4 + CD25 + Regulatory T Cells Resist a Novel Form of CD28- and Fas-Dependent p53-Induced T Cell Apoptosis

Ag receptor stimulation of preactivated T cells causes rapid cell death in an IL-2– and Fas-dependent manner. This phenomenon, known as activation-induced cell death (AICD), plays a pivotal role in the removal of Ag-reactive T cells after initial expansion. In this study, we report a novel form of T cell apoptosis that is distinct from classic AICD. When peripheral T cells were activated with anti-CD3 and anti-CD28 Abs precoated onto plastic plates, CD4+CD25− and CD8 T cells initially expanded but underwent massive apoptosis after 4 d. Unlike classic AICD, this type of T cell apoptosis pathway requires engagement of CD28 and expression of p53, a tumor-suppressor gene. The most striking feature of this form of apoptosis was regulatory T cell resistance. Under the same stimulating conditions, CD4+CD25+ T cells grew continuously beyond 4 d. Consequently, when the entire CD4 population was cultured with plate-bound anti-CD3 plus anti-CD28 Ab, CD4+CD25+FoxP3+ regulatory T cells outgrew nonregulatory T cells and expanded >7000-fold after 11 d. The data presented herein demonstrate a novel process of Ag-induced T cell death by sustained TCR and CD28 engagement and represent a simple and efficient procedure for the expansion of regulatory T cells in vitro.

Molecular and Genetic Insights Into T Cell Antigen Receptor Signal Transduction

T lymphocytes are relatively quiescent cells, poised in the G0 stage of the cell cycle, until they encounter antigen. The initiation of an immune response by T cells requires the recognition of antigen by the T cell antigen receptor (TCR) and the conversion of this recognition event into biochemical signals that can induce a cellular response. This cellular response leads to the clonal expansion of antigen-specific differentiated effector T cells.

TGF-β Converts Apoptotic Stimuli into the Signal for Th9 Differentiation

Naturally arising CD4+CD25+FoxP3+ regulatory T cells (nTregs) have an essential role in maintenance of immune homeostasis and peripheral tolerance. Previously, we reported that conventional CD4+ and CD8+ T cells undergo p53-induced CD28-dependent apoptosis (PICA) when stimulated with a combination of immobilized anti-CD3 and anti-CD28 Abs, whereas nTregs expand robustly under the same conditions, suggesting that there is a differential survival mechanism against PICA between conventional T cells and nTregs. In this study, we demonstrate that TGF-β signaling is required for nTregs to survive PICA. Conversely, when an active form of exogenous TGF-β is present, conventional T cells become resistant to PICA and undergo robust expansion instead of apoptosis, with reduction of the proapoptotic protein Bim and FoxO3a. A substantial fraction of PICA-resistant T cells expressed IL-9 (TH9 cells). Moreover, the presence of IL-6 along with TGF-β led to the generation of TH17 cells from conventional T cells. Together, the data demonstrate a novel role for TGF-β in the homeostasis of regulatory T cells and effector T cell differentiation and expansion.