Kazuo Sugamura

Cutting edge : the common gamma-chain is an indispensable subunit of the IL-21 receptor complex

The common γ-chain (γc) is an indispensable subunit of the functional receptor complexes for IL-4, IL-7, IL-9, and IL-15 as well as IL-2. Here we show that the γc is also shared with the IL-21R complex. Although IL-21 binds to the IL-21R expressed on γc-deficient ED40515− cells, IL-21 is unable to transduce any intracytoplasmic signals. However, in EDγ-16 cells, a γc-transfected ED40515− cell line, IL-21 binds to the IL-21R and can activate Janus kinase (JAK)1, JAK3, STAT1, and STAT3. The chemical cross-linking study reveals the direct binding of IL-21 to the γc. These data clearly demonstrate that the γc is an indispensable subunit of the functional IL-21R complex.

Cell-fate conversion of lymphoid-committed progenitors by instructive actions of cytokines

The primary role of cytokines in haemato-lymphopoiesis is thought to be the regulation of cell growth and survival. But the instructive action of cytokines in haematopoiesis has not been well addressed. Here we show that a clonogenic common lymphoid progenitor, a bone marrow-resident cell that gives rise exclusively to lymphocytes (T, B and natural killer cells), can be redirected to the myeloid lineage by stimulation through exogenously expressed interleukin (IL)-2 and GM-CSF (granulocyte/macrophage colony-stimulating factor) receptors. Analysis of mutants of the β-chain of the IL-2 receptor revealed that the granulocyte- and monocyte-differentiation signals are triggered by different cytoplasmic domains, showing that the signalling pathway(s) responsible for these unique developmental outcomes are separable. Finally, we show that the endogenous myelo-monocytic cytokine receptors for GM-CSF and macrophage colony-stimulating factor (M-CSF) are expressed at low to moderate levels on the more primitive haematopoietic stem cells, are absent on common lymphoid progenitors, and are upregulated after myeloid lineage induction by IL-2. We conclude that cytokine signalling can regulate cell-fate decisions and propose that a critical step in lymphoid commitment is downregulation of cytokine receptors that drive myeloid cell development.

Positional identification of TNFSF4, encoding OX40 ligand, as a gene that influences atherosclerosis susceptibility

Ath1 is a quantitative trait locus on mouse chromosome 1 that renders C57BL/6 mice susceptible and C3H/He mice resistant to diet-induced atherosclerosis. The quantitative trait locus region encompasses 11 known genes, including Tnfsf4 (also called Ox40l or Cd134l), which encodes OX40 ligand. Here we report that mice with targeted mutations of Tnfsf4 had significantly (P ≤ 0.05) smaller atherosclerotic lesions than did control mice. In addition, mice overexpressing Tnfsf4 had significantly (P ≤ 0.05) larger atherosclerotic lesions than did control mice. In two independent human populations, the less common allele of SNP rs3850641 in TNFSF4 was significantly more frequent (P ≤ 0.05) in individuals with myocardial infarction than in controls. We therefore conclude that Tnfsf4 underlies Ath1 in mice and that polymorphisms in its human homolog TNFSF4 increase the risk of myocardial infarction in humans.

Distinct Roles for the OX40-OX40 Ligand Interaction in Regulatory and Nonregulatory T Cells

The OX40 (CD134) molecule is induced primarily during T cell activation and, as we show in this study, is also expressed on CD25+CD4+ regulatory T (Treg) cells. A necessary role for OX40 in the development and homeostasis of Treg cells can be inferred from the reduced numbers of the cells present in the spleens of OX40-deficient mice, and their elevated numbers in the spleens of mice that overexpress the OX40 ligand (OX40L). The homeostatic proliferation of Treg cells following transfer into lymphopenic mice was also found to be potentiated by the OX40-OX40L interaction. Suppression of T cell responses by Treg cells was significantly impaired in the absence of OX40, indicating that, in addition to its homeostatic functions, OX40 contributes to efficient Treg-mediated suppression. However, despite this, we found that CD25−CD4+ T cells became insensitive to Treg-mediated suppression when they were exposed to OX40L-expressing cells, or when they were treated with an agonistic OX40-specific mAb. OX40 signaling could also abrogate the disease-preventing activity of Treg cells in an experimental model of inflammatory bowel disease. Thus, although the data reveal important roles for OX40 signaling in Treg cell development, homeostasis, and suppressive activity, they also show that OX40 signals can oppose Treg-mediated suppression when they are delivered directly to Ag-engaged naive T cells.

Therapeutic targeting of the effector T-cell co-stimulatory molecule OX40.

An emerging immunotherapeutic strategy for T-cell-mediated diseases is to directly target antigen-specific T cells that are responsible for the clinical effects, without causing general widespread immunosuppression. A T-cell co-stimulatory molecule, OX40, which is transiently expressed after antigen recognition, fits these criteria in several immune-mediated diseases. In vivo blockade of OX40 signalling specifically suppresses the function of recently activated autoantigen-specific T cells, leading to inhibition of autoimmune disease without severe immunosuppression. In addition, deliberate ligation of OX40 in tumour-bearing hosts enhances anticancer immunity. We discuss how targeting OX40 is potentially an ideal strategy for immune-based therapies in several human diseases.

CRTH2, an orphan receptor of T‐helper‐2‐cells, is expressed on basophils and eosinophils and responds to mast cell‐derived factor(s)

We have recently cloned a putative chemoattractant receptor, named CRTH2, which is preferentially expressed on human T‐helper‐ (Th) 2 but not Th1 cells. In this study, we demonstrated that CRTH2 is also highly expressed on peripheral blood basophils and eosinophils. Our search for a CRTH2 ligand identified mast cells as the possible producers of a ligand. When stimulated with an anti‐FcϵR1 antibody, cord blood‐derived mast cells secreted factor(s) that induced Ca2+ mobilization in CRTH2‐expressing K562 cells but not in mock transfected cells. These findings implied the involvement of CRTH2 in mast cell‐mediated immune responses such as allergic reactions.

Bcl-2 Rescues T Lymphopoiesis, but Not B or NK Cell Development, in Common γ Chain–Deficient Mice

The common cytokine receptor gamma chain (gamma(c)) is an indispensable subunit for the formation of lymphoid-related cytokine receptors, including IL-7 and IL-15 receptors, that mediate nonredundant or critical signals for the differentiation of T and B cells and natural killer (NK) cells, respectively. We introduced the bcl-2 transgene driven by E mu or H-2K promoters into gamma(c)-deficient mice that lack all three lymphoid subclasses. The forced expression of Bcl-2 restored all stages of T lymphopoiesis, but not B or NK cell development, indicating that a primary function of gamma(c)-mediated signals in the T lineage might be to maintain cell survival. Therefore, the development of T, B, and NK cells may be influenced by distinct intracytoplasmic signaling cascades that are activated by coupling of gamma(c)-related receptors.

During Viral Infection of the Respiratory Tract, CD27, 4-1BB, and OX40 Collectively Determine Formation of CD8+ Memory T Cells and Their Capacity for Secondary Expansion

Independent studies have shown that CD27, 4-1BB, and OX40 can all promote survival of activated CD8+ T cells. We have therefore compared their impact on CD8+ memory T cell formation and responsiveness within one, physiologically relevant model system. Recombinant mice, selectively lacking input of one or two receptors, were challenged intranasally with influenza virus, and the immunodominant virus-specific CD8+ T cell response was quantified at priming and effector sites. Upon primary infection, CD27 and (to a lesser extent) 4-1BB made nonredundant contributions to accumulation of CD8+ virus-specific T cells in draining lymph nodes and lung, while OX40 had no effect. Interestingly though, in the memory response, accumulation of virus-specific CD8+ T cells in spleen and lung critically depended on all three receptor systems. This was explained by two observations: 1) CD27, 4-1BB, and OX40 were collectively responsible for generation of the same memory CD8+ T cell pool; 2) CD27, 4-1BB, and OX40 collectively determined the extent of secondary expansion, as shown by adoptive transfers with standardized numbers of memory cells. Surprisingly, wild-type CD8+ memory T cells expanded normally in primed OX40 ligand- or 4-1BB ligand-deficient mice. However, when wild-type memory cells were generated in OX40 ligand- or 4-1BB ligand-deficient mice, their secondary expansion was impaired. This provides the novel concept that stimulation of CD8+ T cells by OX40 and 4-1BB ligand during priming imprints into them the capacity for secondary expansion. Our data argue that ligand on dendritic cells and/or B cells may be critical for this.

Cutting Edge: Differential Production of Prostaglandin D2 by Human Helper T Cell Subsets

Several effector molecules, including cytokines, are differentially produced by Th1 and Th2 cells. We used a gene expression screen method to identify a gene encoding hematopoietic PG D synthase (hPGDS) which was preferentially expressed in human Th2 but not Th1 clones. Studies with anti-hPGDS mAbs confirmed the Th2-dominated expression of hPGDS protein. Upon stimulation with anti-CD3 plus anti-CD28 mAbs, coordinated cyclooxygenase-2 expression and PGD2 production were induced in Th2 lines. hPGDS expression was also observed in a small population (<1.0%) of peripheral blood CD4+ lymphocytes from healthy adults. Most hPGDS-expressing CD4+ lymphocytes showed a typical Th2-type cytokine pattern. Our results suggest that, at the sites of Ag presentation, at least part of the Th2 cell population produces PGD2, which may be involved in various aspects of Th2-related immune responses similar to mast cells.

Hrs Is Associated with STAM, a Signal-transducing Adaptor Molecule ITS SUPPRESSIVE EFFECT ON CYTOKINE-INDUCED CELL GROWTH

We previously reported a new type of signal-transducing adaptor molecule, STAM, which was shown to be involved in cytokine-mediated intracellular signal transduction. In this study, we molecularly cloned a 110-kDa phosphotyrosine protein inducible by stimulation with interleukin 2 (IL-2). The 110-kDa molecule was found to be a human counterpart of mouse Hrs (hepatocyte growth factor-regulated tyrosine kinase substrate) and to be associated with STAM. Tyrosine phosphorylation of Hrs is induced rapidly after stimulation with IL-2 and granulocyte-macrophage colony-stimulating factor as well as hepatocyte growth factor. The mutual association sites of Hrs and STAM include highly conserved coiled-coil sequences, suggesting that their association is mediated by the coiled-coil structures. Exogenous introduction of the wild-type Hrs significantly suppressed DNA synthesis upon stimulation with IL-2 and granulocyte-macrophage colony-stimulating factor, while the Hrs mutant deleted of the STAM-binding site lost such suppressive ability. These results suggest that Hrs counteracts the STAM function which is critical for cell growth signaling mediated by the cytokines.