ABSTRACT
Memory T lymphocytes are distinct from antigen-inexperienced naïve T cells in that memory T cells can respond more rapidly when they re-encounter a pathogen. Work over the past decade has begun to define the epigenetic underpinnings of the transcriptional component of the memory T cell response. An emerging theme is the persistence of an active chromatin signature at relevant gene loci in resting memory T cells, even when those genes are transcriptionally inactive. This gives strength to the concept of gene poising, and has shown that memory T lymphocytes are an ideal model in which to further define various mechanisms of epigenetic poising.
Subject(s)
Epigenesis, Genetic , Immunologic Memory , Cell Differentiation , Chromatin , Gene Expression , Humans , T-Lymphocytes/cytology , T-Lymphocytes/immunologyABSTRACT
Memory CD8(+) T cells are characterized by more rapid and robust effector function upon infection compared with naive T cells, but factors governing effector gene responsiveness are incompletely understood. We sought to understand transcriptional control of the effector genes IFN-γ (Ifng), granzyme B (Gzmb), and perforin 1 (Prf1) in murine memory CD8(+) T cells by characterizing their transcriptional profiles and chromatin states during lymphocytic choriomeningitis virus infection. Each effector gene has a distinct transcriptional profile in resting memory cells and following restimulation. Primary infection leads to reduced nucleosomal density near the transcription start sites and reduced H3K27 methylation throughout the Ifng and Gzmb loci, and these chromatin changes persist in the memory phase. Despite similarities in chromatin at the memory stage, PolII recruitment and continuous transcription occur at the Ifng locus but not the Gzmb locus. We propose that these chromatin changes poise effector genes for rapid upregulation, but are insufficient for PolII recruitment and transcription.
Subject(s)
CD8-Positive T-Lymphocytes/immunology , Chromatin/immunology , Genetic Loci/immunology , Immunologic Memory/genetics , Resting Phase, Cell Cycle/immunology , Transcription, Genetic/immunology , Animals , CD8-Positive T-Lymphocytes/enzymology , CD8-Positive T-Lymphocytes/pathology , Cells, Cultured , Chromatin/genetics , Chromatin/virology , Gene Expression Profiling , Granzymes/biosynthesis , Granzymes/genetics , Interferon-gamma/biosynthesis , Interferon-gamma/genetics , Lymphocyte Activation/genetics , Lymphocyte Activation/immunology , Lymphocytic Choriomeningitis/genetics , Lymphocytic Choriomeningitis/immunology , Lymphocytic Choriomeningitis/pathology , Mice , Mice, Inbred C57BL , Mice, Transgenic , Perforin , Pore Forming Cytotoxic Proteins/biosynthesis , Pore Forming Cytotoxic Proteins/genetics , Resting Phase, Cell Cycle/genetics , Transcription Initiation SiteABSTRACT
T cells developing in the thymus are ultimately derived from bone marrow (BM) hematopoietic stem cells (HSCs). An understanding of the developmental steps between HSCs and T cells is important for gaining insight into cancers of the T lineage, improving T cell reconstitution after BM transplantation, and also to help ameliorate immunological defects in aging. In this article, we summarize our current understanding of the inter-related fields of early T cell development and thymic aging, and briefly discuss major unresolved questions in this field.
Subject(s)
Cell Movement/immunology , Hematopoietic Stem Cells/cytology , T-Lymphocytes/cytology , Thymus Gland/cytology , Aging/immunology , Animals , Cell Lineage/immunology , Cytokines/immunology , Hematopoietic Stem Cells/immunology , Humans , T-Lymphocytes/immunology , Thymus Gland/immunologyABSTRACT
In this issue of Molecular Cell, Conaway and colleagues (Yao et al., 2008) provide a glimpse into an interesting mechanism to control a deubiquitylating enzyme via interaction of two complexes-the 19S proteasome regulatory particle and an ATP-dependent nucleosome remodeling complex.
Subject(s)
Carboxypeptidases/metabolism , Chromatin Assembly and Disassembly , DNA Helicases/metabolism , Proteasome Endopeptidase Complex/metabolism , ATPases Associated with Diverse Cellular Activities , Carboxypeptidases/antagonists & inhibitors , Carboxypeptidases/chemistry , DNA-Binding Proteins , Humans , Protein Binding , Protein Subunits/metabolism , Ubiquitin ThiolesteraseABSTRACT
Aging in mice and humans is characterized by declining T-lymphocyte production in the thymus, yet it is unclear whether aging impacts the T-lineage potential of hematopoietic progenitors. Although alterations in the lymphoid progenitor content of aged mouse bone marrow (BM) have been described, irradiation-reconstitution experiments have failed to reveal defects in T-lineage potential of BM hematopoietic progenitors or purified hematopoietic stem cells (HSCs) from aged mice. Here, we assessed T-progenitor potential in unmanipulated recipient mice without conditioning irradiation. T-progenitor potential was reduced in aged BM compared with young BM, and this reduction was apparent at the earliest stages of intrathymic differentiation. Further, enriched populations of aged HSCs or multipotent progenitors (MPPs) gave rise to fewer T-lineage cells than their young counterparts. Whereas the T-precursor frequency within the MPP pool was unchanged, there was a 4-fold decline in T-precursor frequency within the HSC pool. In addition, among the T-competent HSC clones, there were fewer highly proliferative clones in the aged HSC pool than in the young HSC pool. These results identify T-compromised aged HSCs and define the nature and cellular sites of prethymic, age-related defects in T-lineage differentiation potential.
Subject(s)
Aging/pathology , Cell Lineage , Hematopoietic Stem Cells/cytology , Multipotent Stem Cells/cytology , T-Lymphocytes/cytology , Thymus Gland/immunology , Animals , Bone Marrow Cells , Cell Differentiation , Female , Mice , Mice, Inbred C57BL , T-Lymphocytes/immunology , Thymus Gland/pathologyABSTRACT
Developmental abnormalities, cancer, and premature aging each have been linked to defects in the DNA damage response (DDR). Mutations in the ATR checkpoint regulator cause developmental defects in mice (pregastrulation lethality) and humans (Seckel syndrome). Here we show that eliminating ATR in adult mice leads to defects in tissue homeostasis and the rapid appearance of age-related phenotypes, such as hair graying, alopecia, kyphosis, osteoporosis, thymic involution, fibrosis, and other abnormalities. Histological and genetic analyses indicate that ATR deletion causes acute cellular loss in tissues in which continuous cell proliferation is required for maintenance. Importantly, thymic involution, alopecia, and hair graying in ATR knockout mice were associated with dramatic reductions in tissue-specific stem and progenitor cells and exhaustion of tissue renewal and homeostatic capacity. In aggregate, these studies suggest that reduced regenerative capacity in adults via deletion of a developmentally essential DDR gene is sufficient to cause the premature appearance of age-related phenotypes.
Subject(s)
Aging/genetics , Cell Cycle Proteins/genetics , Genes, Essential , Protein Serine-Threonine Kinases/genetics , Stem Cells/cytology , Animals , Ataxia Telangiectasia Mutated Proteins , Mice , Mice, Knockout , PhenotypeABSTRACT
The ARF tumor suppressor protects us against cancer through protein-protein interactions in partially defined p53-dependent and p53-independent pathways. We performed a two-hybrid screen using ARF as bait and present the identification of several new ARF partners that may regulate its growth inhibitory signaling. The potential physiological roles of these novel ARF binding proteins in regulating ARF signaling are discussed.
Subject(s)
Carrier Proteins/genetics , Carrier Proteins/metabolism , Growth Inhibitors/metabolism , Signal Transduction/genetics , Tumor Suppressor Protein p14ARF/metabolism , Animals , COS Cells , Carrier Proteins/isolation & purification , Cell Transformation, Neoplastic/genetics , Cell Transformation, Neoplastic/metabolism , Chlorocebus aethiops , Cyclin-Dependent Kinase Inhibitor p16 , Growth Inhibitors/genetics , Humans , Mice , NIH 3T3 Cells , Protein Binding/genetics , Tumor Suppressor Protein p14ARF/genetics , Two-Hybrid System TechniquesABSTRACT
Questions regarding T cell development have recently received much attention, but the earliest intrathymic differentiation steps in adult mice have remained controversial. Three new papers together show that for at least some thymus-settling precursors, the loss of B lineage potential occurs in the thymus, and Notch acts on multipotent progenitors early after thymic entry.
Subject(s)
Hematopoietic Stem Cells/immunology , Lymphocytes/cytology , Membrane Proteins/immunology , Multipotent Stem Cells/immunology , Thymus Gland/cytology , Animals , Cell Differentiation , Cell Lineage , Hematopoietic Stem Cells/cytology , Humans , Lymphocytes/immunology , Mice , Multipotent Stem Cells/cytology , Receptors, Notch , Thymus Gland/immunologyABSTRACT
Signaling by the transmembrane receptor Notch is critical for T lineage development, but progenitor subsets that first receive Notch signals have not been defined. Here we identify an immature subset of early T lineage progenitors (ETPs) in the thymus that expressed the tyrosine kinase receptor Flt3 and had preserved B lineage potential at low progenitor frequency. Notch signaling was active in ETPs and was required for generation of the ETP population. Additionally, Notch signals contributed to the subsequent differentiation of ETPs. In contrast, multipotent hematopoietic progenitors circulated in the blood even in the absence of Notch signaling, suggesting that critical Notch signals during early T lineage development are delivered early after thymic entry.
Subject(s)
Membrane Proteins/immunology , T-Lymphocytes/immunology , Thymus Gland/immunology , Animals , B-Lymphocytes/cytology , B-Lymphocytes/immunology , Cell Differentiation/immunology , Cell Lineage/immunology , Female , Mice , Mice, Inbred C57BL , Mice, Knockout , Proto-Oncogene Proteins/biosynthesis , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins/immunology , RNA/chemistry , RNA/genetics , Receptor Protein-Tyrosine Kinases/biosynthesis , Receptor Protein-Tyrosine Kinases/genetics , Receptor Protein-Tyrosine Kinases/immunology , Receptors, Notch , Reverse Transcriptase Polymerase Chain Reaction , Signal Transduction/immunology , T-Lymphocyte Subsets/immunology , T-Lymphocytes/cytology , fms-Like Tyrosine Kinase 3ABSTRACT
Thymic involution is the hallmark of hematopoietic aging. Because T cell differentiation is a multistep process that occurs non-cell autonomously, aging defects can occur at multiple points along the developmental pathway, both in the T progenitors themselves and in the thymic stromal cells that support their development. Here we review the evidence for age-related thymopoiesis defects at key steps in the production of naïve mature T cells, highlighting the importance of the interaction between stromal aging and progenitor aging.
Subject(s)
Aging/immunology , Cell Communication/immunology , Cell Differentiation/immunology , Cellular Senescence/immunology , Hematopoietic Stem Cells/immunology , T-Lymphocyte Subsets/immunology , Animals , Hematopoietic Stem Cells/cytology , Humans , T-Lymphocyte Subsets/cytologyABSTRACT
Activated CD8+ T cells play a critical role in host defense against viruses, intracellular microbes, and tumors. It is not clear if a key regulatory transcription factor unites the effector functions of CD8+ T cells. We now show that Eomesodermin (Eomes), a paralogue of T-bet, is induced in effector CD8+ T cells in vitro and in vivo. Ectopic expression of Eomes was sufficient to invoke attributes of effector CD8+ T cells, including interferon-gamma (IFN-gamma), perforin, and granzyme B. Loss-of-function analysis suggests Eomes may also be necessary for full effector differentiation of CD8+ T cells. We suggest that Eomesodermin is likely to complement the actions of T-bet and act as a key regulatory gene in the development of cell-mediated immunity.
Subject(s)
CD8-Positive T-Lymphocytes/immunology , T-Box Domain Proteins/physiology , Amino Acid Sequence , Animals , Arenaviridae Infections/immunology , Base Sequence , CD8-Positive T-Lymphocytes/physiology , Cell Differentiation , Cytotoxicity, Immunologic , Gene Expression Regulation , Granzymes , Interferon-gamma/biosynthesis , Lymphocyte Activation , Lymphocytic choriomeningitis virus/immunology , Membrane Glycoproteins/biosynthesis , Membrane Glycoproteins/genetics , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Molecular Sequence Data , Perforin , Pore Forming Cytotoxic Proteins , RNA, Messenger/genetics , RNA, Messenger/metabolism , Serine Endopeptidases/biosynthesis , Serine Endopeptidases/genetics , T-Box Domain Proteins/chemistry , T-Box Domain Proteins/genetics , Th2 Cells/immunology , Th2 Cells/physiology , Transcription Factors/chemistry , Transcription Factors/genetics , Transcription Factors/physiologyABSTRACT
IL-10 is an inhibitor of the production of pro-inflammatory cytokines such as IL-12 and IL-1beta, but it is not known whether it can inhibit the production of IL-18. Therefore, a variety of in vivo and in vitro models were used to determine whether IL-10 is an inhibitor of IL-18 production. Infection of IL-10-/- mice with Toxoplasma gondii results in increased levels of IL-12 in the serum and in recall responses compared to wild type (WT) mice. Surprisingly, although infection resulted in increased levels of IL-18 in serum, there were no differences between WT and IL-10-/- mice. Moreover, splenocytes from infected WT and IL-10-/- mice produced similar levels of IL-18 and addition of exogenous IL-10 did not inhibit their production of IL-18. To address whether endogenous IL-18 inhibitors were masking increased IL-18 production in the IL-10-/- mice, expression of IL-18 binding protein was examined using RT-PCR. Although infection leads to increased expression of IL-18BP mRNA, no difference was seen between WT and IL-10-/- mice. In addition, splenocytes from IL-10-/- mice produced elevated levels of nitric oxide (NO) compared to WT mice, and NO has been shown to inhibit activity of interleukin-1 converting enzyme (ICE), which is required for IL-18 production. However, the addition of an inhibitor of NO production did not alter the levels of IL-18 produced. Finally, analysis of the levels of cytokine mRNA of macrophages stimulated with LPS and IFN-gamma revealed that although IL-10 is a potent inhibitor of IL-12 mRNA accumulation, it did not inhibit IL-1beta or IL-18. Together, these data indicate that IL-10 is not an inhibitor of the production of IL-18.
Subject(s)
Interleukin-10/physiology , Interleukin-18/biosynthesis , Animals , Cytokines/metabolism , Enzyme-Linked Immunosorbent Assay , Interleukin-10/metabolism , Interleukin-12/metabolism , Interleukin-18/antagonists & inhibitors , Interleukin-18/metabolism , Mice , Mice, Inbred BALB C , Mice, Transgenic , Nitric Oxide/metabolism , RNA, Messenger/metabolism , Reverse Transcriptase Polymerase Chain Reaction , Ribonucleases/metabolism , Spleen/cytology , Spleen/metabolism , Time Factors , Toxoplasma/metabolism , Transcription, GeneticABSTRACT
Long-term resistance to Toxoplasma gondii is dependent on the development of parasite-specific T cells that produce IFN-gamma. CD28 is a costimulatory molecule important for optimal activation of T cells, but CD28(-/-) mice are resistant to T. gondii, demonstrating that CD28-independent mechanisms regulate T cell responses during toxoplasmosis. The identification of the B7-related protein 1/inducible costimulator protein (ICOS) pathway and its ability to regulate the production of IFN-gamma suggested that this pathway may be involved in the CD28-independent activation of T cells required for resistance to T. gondii. In support of this hypothesis, infection of wild-type or CD28(-/-) mice with T. gondii resulted in the increased expression of ICOS by activated CD4(+) and CD8(+) T cells. In addition, both costimulatory pathways contributed to the in vitro production of IFN-gamma by parasite-specific T cells and when both pathways were blocked, there was an additive effect that resulted in almost complete inhibition of IFN-gamma production. Although in vivo blockade of the ICOS costimulatory pathway did not result in the early mortality of wild-type mice infected with T. gondii, it did lead to increased susceptibility of CD28(-/-) mice to T. gondi associated with reduced serum levels of IFN-gamma, increased parasite burden, and increased mortality compared with the control group. Together, these results identify a critical role for ICOS in the protective Th1-type response required for resistance to T. gondii and suggest that ICOS and CD28 are parallel costimulatory pathways, either of which is sufficient to mediate resistance to this intracellular pathogen.