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1.  A Mechanism for the Initiation of the Th2 Response by an Allergen 
Nature immunology  2008;9(3):310-318.
Both metazoan parasites and simple protein allergens induce Th2 regulated immune responses, but the innate immune sensing mechanisms involved are currently unknown. Specifically, the cellular source of cytokines that control Th2 differentiation in vivo has not been defined. Here we show that basophils are activated and recruited to the draining lymph nodes specifically in response to Th2 inducing allergen challenge. Furthermore, we demonstrate that the basophil is the accessory cell type required for Th2 induction in response to protease allergens. Finally, we show that basophils are directly activated by protease allergens and produce Th2 inducing cytokines, including IL-4 and TSLP, which are involved in Th2 differentiation in vivo.
doi:10.1038/ni1558
PMCID: PMC3888112  PMID: 18300366
3.  Lymphatic endothelial mCLCA1 is a ligand for leukocyte LFA-1 and Mac-1 
The lymphatic circulation mediates drainage of fluid and cells from the periphery through lymph nodes, facilitating immune detection of lymph-borne foreign antigens. The 10.1.1 monoclonal antibody recognizes a lymphatic endothelial antigen, here purified by antibody affinity chromatography. SDS-PAGE and mass spectrometry identified mCLCA1 as the 10.1.1 antigen, a 90 kD cell surface protein expressed in lymphatic endothelium and stromal cells of spleen and thymus. The 10.1.1 antibody affinity chromatography also purified LFA-1, an integrin that mediates leukocyte adhesion to endothelium. This mCLCA1-LFA-1 interaction has functional consequences, as lymphocyte adhesion to lymphatic endothelium was blocked by 10.1.1 antibody bound to endothelium, or by LFA-1 antibody bound to lymphocytes. Lymphocyte adhesion was increased by cytokine treatment of lymphatic endothelium, in association with increased expression of ICAM-1, an endothelial surface protein that is also a ligand for LFA-1. By contrast, mCLCA1 expression and the relative contribution of mCLCA1 to lymphocyte adhesion were unaffected by cytokine activation, demonstrating that mCLCA1 and ICAM-1 interactions with LFA-1 are differentially regulated. mCLCA1 also bound to the LFA-1-related Mac-1 integrin that is preferentially expressed on leukocytes. mCLCA1-mediated adhesion of Mac-1- or LFA-1-expressing leukocytes to lymphatic vessels and lymph node lymphatic sinuses provides a new target for investigation of lymphatic involvement in leukocyte adhesion and trafficking during the immune response.
doi:10.4049/jimmunol.1002226
PMCID: PMC3367505  PMID: 20937843
4.  Lymph node–resident lymphatic endothelial cells mediate peripheral tolerance via Aire-independent direct antigen presentation 
Peripheral immune tolerance is generally thought to result from cross-presentation of tissue-derived proteins by quiescent tissue-resident dendritic cells to self-reactive T cells that have escaped thymic negative selection, leading to anergy or deletion. Recently, we and others have implicated the lymph node (LN) stroma in mediating CD8 T cell peripheral tolerance. We demonstrate that LN-resident lymphatic endothelial cells express multiple peripheral tissue antigens (PTAs) independent of the autoimmune regulator (Aire). They directly present an epitope derived from one of these, the melanocyte-specific protein tyrosinase, to tyrosinase-specific CD8 T cells, leading to their deletion. We also show that other LN stromal subpopulations express distinct PTAs by mechanisms that vary in their Aire dependence. These results establish lymphatic endothelial cells, and potentially other LN-resident cells, as systemic mediators of peripheral immune tolerance.
doi:10.1084/jem.20092465
PMCID: PMC2856027  PMID: 20308365
5.  Atopic Dermatitis-Like Disease and Associated Lethal Myeloproliferative Disorder Arise from Loss of Notch Signaling in the Murine Skin 
PLoS ONE  2010;5(2):e9258.
Background
The Notch pathway is essential for proper epidermal differentiation during embryonic skin development. Moreover, skin specific loss of Notch signaling in the embryo results in skin barrier defects accompanied by a B-lymphoproliferative disease. However, much less is known about the consequences of loss of Notch signaling after birth.
Methodology and Principal Findings
To study the function of Notch signaling in the skin of adult mice, we made use of a series of conditional gene targeted mice that allow inactivation of several components of the Notch signaling pathway specifically in the skin. We demonstrate that skin-specific inactivation of Notch1 and Notch2 simultaneously, or RBP-J, induces the development of a severe form of atopic dermatitis (AD), characterized by acanthosis, spongiosis and hyperkeratosis, as well as a massive dermal infiltration of eosinophils and mast cells. Likewise, patients suffering from AD, but not psoriasis or lichen planus, have a marked reduction of Notch receptor expression in the skin. Loss of Notch in keratinocytes induces the production of thymic stromal lymphopoietin (TSLP), a cytokine deeply implicated in the pathogenesis of AD. The AD-like associated inflammation is accompanied by a myeloproliferative disorder (MPD) characterized by an increase in immature myeloid populations in the bone marrow and spleen. Transplantation studies revealed that the MPD is cell non-autonomous and caused by dramatic microenvironmental alterations. Genetic studies demontrated that G-CSF mediates the MPD as well as changes in the bone marrow microenvironment leading to osteopenia.
Significance
Our data demonstrate a critical role for Notch in repressing TSLP production in keratinocytes, thereby maintaining integrity of the skin and the hematopoietic system.
doi:10.1371/journal.pone.0009258
PMCID: PMC2823782  PMID: 20174635
6.  Notch ligands Delta1 and Jagged1 transmit distinct signals to T-cell precursors 
Blood  2004;105(4):1440-1447.
Signaling through the Notch pathway plays an essential role in inducing T-lineage commitment and promoting the maturation of immature thymocytes. Using an in vitro culture system, we show that 2 different classes of Notch ligands, Jagged1 or Delta1, transmit distinct signals to T-cell progenitors. OP9 stromal cells expressing either Jagged1 or Delta1 inhibit the differentiation of DN1 thymocytes into the B-cell lineage, but only the Delta1-expressing stromal cells promote the proliferation and maturation of T-cell progenitors through the early double-negative (DN) stages of thymocyte development. Whereas the majority of bone marrow-derived stem cells do not respond to Jagged1 signals, T-cell progenitors respond to Jagged1 signals during a brief window of their development between the DN1 and DN3 stages of thymic development. During these stages, Jagged1 signals can influence the differentiation of immature thymocytes along the natural killer (NK) and γδ T-cell lineages.
doi:10.1182/blood-2004-08-3257
PMCID: PMC2776671  PMID: 15486060
7.  Alterations of the medullary epithelial compartment in the Aire-deficient thymus: Implications for programs of thymic epithelial differentiation1 
A widely held model of thymic epithelial differentiation is based on patterns of keratin expression, where a K8+K5+ progenitor gives rise to K8+K5/K14− cortical thymic epithelium (CTEC), and medullary thymic epithelium (MTEC) is K8−K5+K14+. The thymic phenotype of p63-deficient mice indicates that p63 is an important regulator of proximal stages of TE differentiation. In this study we have examined several features of the thymic medullary compartment in WT and Aire-deficient thymi in an effort to integrate the pro-apoptotic activity of Aire with these different perspectives of TE differentiation. Patterns of keratin and p63 expression by MTEC described here are difficult to reconcile with postmitotic MTEC that express a K8−K14+ phenotype and suggest that the patterns of p63 and keratin expression reflecting differentiation programs of other epithelial tissues provide a useful framework for revising models of TE differentiation. Alterations of the Aire−/− MTEC compartment included reduced expression of p63, increased frequency of MTEC expressing truncated Aire protein, and shifts in the pattern of keratin expression and epithelial morphology. These data suggest a scenario where cellular targets of Aire-mediated apoptosis are postmitotic MTEC that have not yet completed their terminal differentiation program. According to this view, the minor population of globular K8+K14−/low MTEC observed in the Aire+/+ thymus and that are significantly expanded in the Aire−/− thymic medulla represent end-stage, terminally differentiated MTEC. These Aire-dependent alterations of the MTEC compartment suggest that the activity of Aire is not neutral with respect to the program of MTEC differentiation.
PMCID: PMC2677919  PMID: 18832676
Thymus; Aire; p63; claudin; differentiation
9.  Notch-Deficient Skin Induces a Lethal Systemic B-Lymphoproliferative Disorder by Secreting TSLP, a Sentinel for Epidermal Integrity 
PLoS Biology  2008;6(5):e123.
Epidermal keratinocytes form a highly organized stratified epithelium and sustain a competent barrier function together with dermal and hematopoietic cells. The Notch signaling pathway is a critical regulator of epidermal integrity. Here, we show that keratinocyte-specific deletion of total Notch signaling triggered a severe systemic B-lymphoproliferative disorder, causing death. RBP-j is the DNA binding partner of Notch, but both RBP-j–dependent and independent Notch signaling were necessary for proper epidermal differentiation and lipid deposition. Loss of both pathways caused a persistent defect in skin differentiation/barrier formation. In response, high levels of thymic stromal lymphopoietin (TSLP) were released into systemic circulation by Notch-deficient keratinocytes that failed to differentiate, starting in utero. Exposure to high TSLP levels during neonatal hematopoiesis resulted in drastic expansion of peripheral pre- and immature B-lymphocytes, causing B-lymphoproliferative disorder associated with major organ infiltration and subsequent death, a previously unappreciated systemic effect of TSLP. These observations demonstrate that local skin perturbations can drive a lethal systemic disease and have important implications for a wide range of humoral and autoimmune diseases with skin manifestations.
Author Summary
Skin is the largest organ of the body, forming an elaborate barrier that prevents water loss and protects the internal environment from outside invaders. When this barrier is compromised, keratinocytes, keratin-producing epidermal cells, alert and recruit the immune cells to the site of the breach as part of an adaptive defense mechanism. However, chronic activation of such an “alarm” could have undesired consequences. Using genetic engineering to progressively remove components of Notch signaling from mouse skin in utero resulted in chronic skin-barrier defects, mimicking a form of human skin disease called atopic dermatitis. Surprisingly, we discovered that a persistent alarm signal in newborns triggered a systemic B-lymphoproliferative disorder, which precisely mirrored the degree of skin defect and was lethal in its extreme form. This alarm signal, in the form of a cytokine called thymic stromal lymphopoietin, was produced by Notch-deficient keratinocytes that failed to form a competent skin barrier. Therefore, we uncovered a long-range proliferative effect on fetal pre-B cells in vivo that is induced by injured skin and mediated by thymic stromal lymphopoietin. These findings highlight the central role that skin-derived factors can play in initiating systemic diseases with skin involvement.
A skin-derived factor plays a lead role in initiating a lethal systemic disease. The current findings point to a novel impact of Notch-deficient skin on hematopoiesis, where unique biology of a keratinocyte-derived cytokine contributes to a severe neonatal blood disease.
doi:10.1371/journal.pbio.0060123
PMCID: PMC2430908  PMID: 18507503
10.  Lack of Foxp3 function and expression in the thymic epithelium 
Foxp3 is essential for the commitment of differentiating thymocytes to the regulatory CD4+ T (T reg) cell lineage. In humans and mice with a genetic Foxp3 deficiency, absence of this critical T reg cell population was suggested to be responsible for the severe autoimmune lesions. Recently, it has been proposed that in addition to T reg cells, Foxp3 is also expressed in thymic epithelial cells where it is involved in regulation of early thymocyte differentiation and is required to prevent autoimmunity. Here, we used genetic tools to demonstrate that the thymic epithelium does not express Foxp3. Furthermore, we formally showed that genetic abatement of Foxp3 in the hematopoietic compartment, i.e. in T cells, is both necessary and sufficient to induce the autoimmune lesions associated with Foxp3 loss. In contrast, deletion of a conditional Foxp3 allele in thymic epithelial cells did not result in detectable changes in thymocyte differentiation or pathology. Therefore, in mice the only known role for Foxp3 remains promotion of T reg cell differentiation within the T cell lineage, whereas there is no role for Foxp3 in thymic epithelial cells.
doi:10.1084/jem.20062465
PMCID: PMC2137899  PMID: 17353370
11.  Developmental regulation of Foxp3 expression during ontogeny 
Thymectomy of neonatal mice can result in the development of autoimmune pathology. It has been proposed that thymic output of regulatory T (T reg) cells is delayed during ontogeny and that the development of autoimmune disease in neonatally thymectomized mice is caused by the escape of self-reactive T cells before thymectomy without accompanying T reg cells. However, the kinetics of T reg cell production within the thymus during ontogeny has not been assessed. We demonstrate that the development of Foxp3-expressing T reg cells is substantially delayed relative to nonregulatory thymocytes during ontogeny. Based on our data, we speculate that induction of Foxp3 in developing thymocytes and, thus, commitment to the T reg cell lineage is facilitated by a signal largely associated with the thymic medulla.
doi:10.1084/jem.20050784
PMCID: PMC2213175  PMID: 16203863
12.  Contrasting models of promiscuous gene expression by thymic epithelium 
Medullary thymic epithelial cells (mTECs) express a broad spectrum of tissue- restricted self-antigens (TRAs), which are required for the development of central tolerance. A new study suggests that TRA expression is a specialized property of terminally differentiated mTECs. However, as discussed here, an alternative model—whereby TRA expression is regulated by conserved developmental programs active in developing mTECs—may be equally plausible.
doi:10.1084/jem.20050976
PMCID: PMC2212887  PMID: 15983067
13.  Cloning of the Murine Thymic Stromal Lymphopoietin (Tslp) Receptor 
The cellular receptor for murine thymic stromal lymphopoietin (TSLP) was detected in a variety of murine, but not human myelomonocytic cell lines by radioligand binding. cDNA clones encoding the receptor were isolated from a murine T helper cell cDNA library. TSLP receptor (TSLPR) is a member of the hematopoietin receptor family. Transfection of TSLPR cDNA resulted in only low affinity binding. Cotransfection of the interleukin 7 (IL-7)Rα chain cDNA resulted in conversion to high affinity binding. TSLP did not activate cells from IL-7Rα−/− mice, but did activate cells from γc−/− mice. Thus, the functional TSLPR requires the IL-7Rα chain, but not the γc chain for signaling.
PMCID: PMC2193276  PMID: 10974032
cytokine receptors; interleukin 2 receptor; interleukin 7 receptor; cytokine; DNA sequence
14.  A Role for Endogenous Transforming Growth Factor β1 in Langerhans Cell Biology:  The Skin of   Transforming Growth Factor β1 Null Mice Is Devoid of  Epidermal Langerhans Cells 
The Journal of Experimental Medicine  1996;184(6):2417-2422.
Transforming growth factor β1 (TGF-β1) regulates leukocytes and epithelial cells. To determine whether the pleiotropic effects of TGF-β1, a cytokine that is produced by both keratinocytes and Langerhans cells (LC), extend to epidermal leukocytes, we characterized LC (the epidermal contingent of the dendritic cell [DC] lineage) and dendritic epidermal T cells (DETC) in TGF-β1 null (TGF-β1 −/−) mice. I-A+ LC were not detected in epidermal cell suspensions or epidermal sheets prepared from TGF-β1 −/− mice, and epidermal cell suspensions were devoid of allostimulatory activity. In contrast, TCR-γδ+ DETC were normal in number and appearance in TGF-β1 −/− mice and, importantly, DETC represented the only leukocytes in the epidermis. Immunolocalization studies revealed CD11c+ DC in lymph nodes from TGF-β1 −/− mice, although gp40+ DC were absent. Treatment of TGF-β1 −/− mice with rapamycin abrogated the characteristic inflammatory wasting syndrome and prolonged survival indefinitely, but did not result in population of the epidermis with LC. Thus, the LC abnormality in TGF-β1 −/− mice is not a consequence of inflammation in skin or other organs, and LC development is not simply delayed in these animals. We conclude that endogenous TGF-β1 is essential for normal murine LC development or epidermal localization.
PMCID: PMC2196398  PMID: 8976197
15.  Visualization and Identification of IL-7 Producing Cells in Reporter Mice 
PLoS ONE  2009;4(11):e7637.
Interleukin-7 (IL-7) is required for lymphocyte development and homeostasis although the actual sites of IL-7 production have never been clearly identified. We produced a bacterial artificial chromosome (BAC) transgenic mouse expressing ECFP in the Il7 locus. The construct lacked a signal peptide and ECFP (enhanced cyan fluorescent protein ) accumulated inside IL-7-producing stromal cells in thoracic thymus, cervical thymus and bone marrow. In thymus, an extensive reticular network of IL-7-containing processes extended from cortical and medullary epithelial cells, closely contacting thymocytes. Central memory CD8 T cells, which require IL-7 and home to bone marrow, physically associated with IL-7-producing cells as we demonstrate by intravital imaging.
doi:10.1371/journal.pone.0007637
PMCID: PMC2770321  PMID: 19907640

Results 1-15 (15)