Motonari Kondo

Identification of Clonogenic Common Lymphoid Progenitors in Mouse Bone Marrow

The existence of a common lymphoid progenitor that can only give rise to T cells, B cells, and natural killer (NK) cells remains controversial and constitutes an important gap in the hematopoietic lineage maps. Here, we report that the Lin(-)IL-7R(+)Thy-1(-)Sca-1loc-Kit(lo) population from adult mouse bone marrow possessed a rapid lymphoid-restricted (T, B, and NK) reconstitution capacity in vivo but completely lacked myeloid differentiation potential either in vivo or in vitro. A single Lin(-)IL-7R(+)Thy-1(-)Sca-1loc-Kit(lo) cell could generate at least both T and B cells. These data provide direct evidence for the existence of common lymphoid progenitors in sites of early hematopoiesis.

Bcl-2 Rescues T Lymphopoiesis in Interleukin-7 Receptor–Deficient Mice

Mice lacking functional IL-7 or IL-7R alpha genes are severely deficient in developing thymocytes, T cells, and B cells. IL-7 and IL-7 receptor functions are believed to result in lymphoid cell proliferation and cell maturation, implying signal transduction pathways directly involved in mitogenesis and elaboration of developmentally specific new gene programs. Here, we show that enforced expression of the bcl-2 gene in T-lymphoid cells (by crossing in the Emu-bcl-2 transgene) in IL-7R alpha-deficient mice results in a significant restoration of thymic positive selection and T cell numbers and function. We propose cell survival signals to be the principal function of IL-7R engagement in thymic and T cell development.

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.

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.

IL-7 receptor signaling is necessary for stage transition in adult B cell development through up-regulation of EBF

Cytokine receptor signals have been suggested to stimulate cell differentiation during hemato/lymphopoiesis. Such action, however, has not been clearly demonstrated. Here, we show that adult B cell development in IL-7 −/− and IL-7Rα2/− mice is arrested at the pre–pro-B cell stage due to insufficient expression of the B cell–specific transcription factor EBF and its target genes, which form a transcription factor network in determining B lineage specification. EBF expression is restored in IL-7 −/− pre–pro-B cells upon IL-7 stimulation or in IL-7Rα−/− pre–pro-B cells by activation of STAT5, a major signaling molecule downstream of the IL-7R signaling pathway. Furthermore, enforced EBF expression partially rescues B cell development in IL-7Rα−/− mice. Thus, IL-7 receptor signaling is a participant in the formation of the transcription factor network during B lymphopoiesis by up-regulating EBF, allowing stage transition from the pre–pro-B to further maturational stages.

Inflammation Controls B Lymphopoiesis by Regulating Chemokine CXCL12 Expression

Inflammation removes developing and mature lymphocytes from the bone marrow (BM) and induces the appearance of developing B cells in the spleen. BM granulocyte numbers increase after lymphocyte reductions to support a reactive granulocytosis. Here, we demonstrate that inflammation, acting primarily through tumor necrosis factor α (TNFα), mobilizes BM lymphocytes. Mobilization reflects a reduced CXCL12 message and protein in BM and changes to the BM environment that prevents homing by cells from naive donors. The effects of TNFα are potentiated by interleukin 1 β (IL-1β), which acts primarily to expand the BM granulocyte compartment. Our observations indicate that inflammation induces lymphocyte mobilization by suppressing CXCL12 retention signals in BM, which, in turn, increases the ability of IL-1β to expand the BM granulocyte compartment. Consistent with this idea, lymphocyte mobilization and a modest expansion of BM granulocyte numbers follow injections of pertussis toxin. We propose that TNFα and IL-1β transiently specialize the BM to support acute granulocytic responses and consequently promote extramedullary lymphopoiesis.

The Common γ-Chain for Multiple Cytokine Receptors

Publisher Summary The chapter focuses on the common γ chain for multiple cytokine receptors. The signal transducers are composed of both common and specific molecules for the cytokines, resulting in overlapping and pleiotropic functions on various target cells in similar situations to other cytokines that share the common receptor subunits. Elucidation of the modes of signal transduction from IL-2Rγ together with the accompanied subunits will lead to the demonstration of regulatory mechanisms of early T-cell development as well as cellular responses to the ligands. Since no intrinsic effectors function has been seen with cytokine receptors sharing IL-2Rγ, signal transducers are assumed to be associated with the cytoplasmic domains of the receptor subunits. Molecular identification of IL-2Rγ has led to knowledge for understanding the structures and signal-transducing functions of various cytokine receptors, and particularly has made a great contribution toward elucidation of the molecular mechanisms of human XSCID occurrence. IL-BRγ, so-called as the “γc-chain”, is utilized as a common receptor subunit among multiple cytokines such as IL- 2, IL-4, IL-7, IL-9, and IL-15. Mutations of IL-2Rγ in patients with XSCID cause dysfunction of these cytokines, resulting in impairment of early T-cell development, a typical feature of XSCID. These cytokine receptors contain specific subunit(s) for each receptor along with the γc-chain. The γc-chain participates in increasing ligands-binding affinities, except for IL-9, and in intracellular signal transduction for all these cytokines.

Role of interleukin-7 in T-cell development from hematopoietic stem cells

Summary: All lymphocytes are derived from hematopoietic stem cells (HSC). The interleukin‐7 receptor (IL‐7R) transduces non‐redundant signals for both T and B‐cell development from HSC. The upregulation of the IL‐7R occurs at the stage of the clonogenic common lymphoid progenitor, a recently identified population that can give rise to all lymphoid lineages (T, B and natural killer cells) at a single cell level. The IL‐7R plays a critical role in the rearrangement of immunoglobulin heavy chain genes required for B‐cell development, IL‐7R expression is critically regulated in developing thymocytes; thytnocytes that fail the positive selection process down‐regulate the IL‐7R, but those undergoing positive selection upregulate or maintain IL‐7R expression. Recent data indicate that IL‐7 signaling enhances the survival of developing thymocytes and mature T ceils, presumably by its upregulating Bcl‐2. Detailed analysis of the signaling cascades activated by the IL‐7R may help to reveal the differential roles of IL‐7 signaling in T and B‐cell development.

Lineage infidelity in myeloid cells with TCR gene rearrangement: A latent developmental potential of proT cells revealed by ectopic cytokine receptor signaling

The most immature lymphoid-committed progenitors in both the bone marrow (common lymphoid progenitor) and thymus (proT1) maintain a latent granulocyte/macrophage (G/M) differentiation potential that can be initiated by signals emanating from exogenously expressed IL-2 receptors. In this study, we investigate at which developmental stage thymocytes lose this G/M differentiation potential. We demonstrate that the next maturational stage after proT1 cells (proT2), but not preT (TN3) cells, can convert cell fate from lymphoid to myeloid in response to ectopic IL-2 receptor signaling in human IL-2Rβ transgenic mice. It is significant that approximately 10% of clonogenic G/M colonies derived from proT cells of IL-2Rβ transgenic mice have DJ rearrangement specifically at the Dβ1 but not Dβ2 segment in the TCRβ locus. No TCR gene rearrangement is observed in G/M cells from nontransgenic mice, suggesting that the G/M cells we observe in this system were truly lymphoid-committed before stimulation with IL-2. In addition, Dβ1 and Dβ2 DJ rearrangement of the TCRβ gene may be differentially regulated and thus serve as markers for distinct proT cell maturational stages.

Identification of a bone marrow precursor of the earliest thymocytes in adult mouse

The thymus requires continuous replenishment of progenitors from the bone marrow (BM) to sustain T cell development. However, it remains unclear which hematopoietic progenitors downstream from hematopoietic stem cells in the BM home to the thymus in adult mice. In this work, we demonstrate that although multiple BM populations have intrinsic T lineage differentiation potential, a small subset of multipotent progenitors (MPPs) expressing CCR9 preferentially homes to the thymus. These CCR9+ MPPs are phenotypically similar to the most immature early T lineage progenitors (ETPs) in the thymus and are present in the peripheral blood. Similar to ETPs, CCR9+ MPPs undergo Notch signaling, as indicated by higher expression of Notch1 and downstream target Hes1 genes compared with other MPP subsets. Furthermore, CCR9+ MPPs possess differentiation potential similar to that of ETPs, with very limited granulocyte/macrophage differentiation potential, but they can differentiate into T, B, and dendritic cells. These characteristics implicate CCR9+ MPPs as the BM precursors of the earliest thymic progenitors. In addition, our data suggest that before transition from BM to thymus, MPPs are lymphoid-specified and primed for T lineage differentiation.