The Lymphatic Endothelial mCLCA1 Antibody Induces Proliferation and Growth of Lymph Node Lymphatic Sinuses.

Lymphocyte- and leukocyte-mediated lymph node (LN) lymphatic sinus growth (lymphangiogenesis) is involved in immune responses and in diseases including cancer and arthritis. We previously discovered a 10.1.

Lymphatic endothelial murine chloride channel calcium-activated 1 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 Ags. The 10.1.

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).

Atopic dermatitis-like disease and associated lethal myeloproliferative disorder arise from loss of Notch signaling in the murine skin.

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.

Visualization and identification of IL-7 producing cells in reporter mice.

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.

Lessons from thymic epithelial heterogeneity: FoxN1 and tissue-restricted gene expression by extrathymic, endodermally derived epithelium.

Modeling of thymic epithelial differentiation has been guided by several important underlying assumptions. One is that within epithelial tissues derived from pharyngeal endoderm, FoxN1 expression is signature for the thymic epithelial lineage. Another is that expression of tissue-restricted Ag (TRA) is a unique feature of thymic epithelium.

Alterations of the medullary epithelial compartment in the Aire-deficient thymus: implications for programs of thymic epithelial differentiation.

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) are K8(-)K5(+)K14(+). The thymic phenotype of p63-deficient mice indicates that p63 is an important regulator of proximal stages of thymic epithelial differentiation. In this study, we have examined several features of the thymic medullary compartment in wild-type and Aire-deficient thymi in an effort to integrate the proapoptotic activity of Aire with these different perspectives of TE differentiation.

Differentiation of regulatory Foxp3+ T cells in the thymic cortex.

Regulatory Foxp3(+) T cells (T(R)) are indispensable for preventing autoimmune pathology in multiple organs and tissues. During thymic differentiation T cell receptor (TCR)-ligand interactions within a certain increased affinity range, in conjunction with gammac-containing cytokine receptor signals, induce Foxp3 expression and thereby commit developing thymocytes to the T(R) lineage. The contribution of distinct MHC class II-expressing accessory cell types to the differentiation process of Foxp3(+) thymocytes remains controversial, because a unique role in this process has been ascribed to either thymic dendritic cells (tDC) or to medullary thymic epithelial cells (mTEC).

Notch-deficient skin induces a lethal systemic B-lymphoproliferative disorder by secreting TSLP, a sentinel for epidermal integrity.

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.

A mechanism for the initiation of allergen-induced T helper type 2 responses.

Both metazoan parasites and simple protein allergens induce T helper type 2 (TH2) immune responses, but the mechanisms by which the innate immune system senses these stimuli are unknown. In addition, the cellular source of cytokines that control TH2 differentiation in vivo has not been defined. Here we showed that basophils were activated and recruited to the draining lymph nodes specifically in response to TH2-inducing allergen challenge.

FGFR2IIIb signaling regulates thymic epithelial differentiation.

Heterogeneous epithelial populations comprising the thymic environment influence early and late stages of T-cell development. The processes that regulate the differentiation of thymic epithelium and that are responsible for this heterogeneity are not well understood, although mesenchymal/epithelial interactions are clearly involved. Here, we show that targeted expression by thymocytes of an fibroblast growth factor receptor-2IIIb (FGFR2IIIb) ligand, FGF10, profoundly alters the differentiation and function of thymic epithelium (TE).

Increased TSLP availability restores T- and B-cell compartments in adult IL-7 deficient mice.

Interleukin 7 (IL-7) plays a crucial role in adult lymphopoiesis, while in fetal life its effect can be partially compensated by TSLP. Whether adult hematopoietic progenitor cells are unresponsive to TSLP or whether TSLP is less available in adult microenvironments is still a matter of debate. Here, we show that increased TSLP availability through transgene (Tg) expression fully restored lymphopoiesis in IL-7-deficient mice: it rescued B-cell development, increased thymic and splenic cellularities, and restored double-negative (DN) thymocytes, alphabeta and gammadelta T-cell generation, and all peripheral lymphoid compartments.

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.

Thymic stromal lymphopoietin transgenic mice develop cryoglobulinemia and hepatitis with similarities to human hepatitis C liver disease.

Essential mixed cryoglobulinemia in humans is strongly associated with chronic hepatitis C virus infection. It remains controversial whether liver injury in hepatitis C is primarily attributable to direct viral cytopathic effect or to an immune-mediated response. We characterized the role of cryoglobulinemia in the development of liver disease in thymic stromal lymphopoietin (TSLP) transgenic mice that produce mixed cryoglobulinemia and develop hepatitis.

Aire-dependent alterations in medullary thymic epithelium indicate a role for Aire in thymic epithelial differentiation.

The prevalent view of thymic epithelial differentiation and Aire activity holds that Aire functions in terminally differentiated medullary thymic epithelial cells (MTECs) to derepress the expression of structural tissue-restricted Ags, including pancreatic endocrine hormones. An alternative view of these processes has proposed that Aire functions to regulate the differentiation of immature thymic epithelial cells, thereby affecting tissue-restricted Ag expression and negative selection. In this study, we demonstrate that Aire impacts several aspects of murine MTECs and provide support for this second model.

A VEGF165-induced phenotypic switch from increased vessel density to increased vessel diameter and increased endothelial NOS activity.

Although vascular endothelial growth factor-165 (VEGF(165)) regulates numerous angiogenic cellular activities, its complex effects on vascular morphology are not highly quantified. By fractal-based, multiparametric branching analysis of 2D vascular pattern in the quail chorioallantoic membrane (CAM), we report that vessel density increased maximally at lower VEGF concentrations, but that vessel diameter and activity of endothelial nitric oxide synthase (eNOS) increased maximally at higher VEGF concentrations. Following exogenous application of human VEGF(165) to the CAM at embryonic day 7, vessel density and diameter were measured after 24 h at arterial end points by the fractal dimension (D(f)) and generational branching parameters for vessel area density (A(v)), vessel length density (L(v)) and vessel diameter (D(v)) using the computer code VESGEN.

Cervical thymus in the mouse.

Although thymic ectopy has long been recognized in humans, the functional activity or potential immunological significance of this thymic tissue is unknown. In this study, we describe murine thymic ectopy, cervical thymic tissue that possesses the same general organization as the thoracic thymus, that is able to support T cell differentiation, and that can export T cells to the periphery. Unexpectedly, the pattern of autoantigen expression by ectopic thymic tissue differs from that of the thoracic thymus, raising the possibility that these two thymic environments may project different versions of self.

Features of medullary thymic epithelium implicate postnatal development in maintaining epithelial heterogeneity and tissue-restricted antigen expression.

Although putative thymic epithelial progenitor cells have been identified, the developmental potential of these cells, the extent of medullary thymic epithelium (mTEC) heterogeneity, and the mechanisms that mediate the expression of a wide range of peripheral tissue-restricted Ags (TRAs) by mTECs remain poorly defined. Here we have defined several basic properties of the mTEC population that refine our understanding of these cells and impose important constraints for any model of mTEC differentiation and function. We report here that mTECs from adult mice are mitotically active, implying continual turnover, differentiation, and replacement of mTEC populations in the adult thymus.

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.

An organized medullary epithelial structure in the normal thymus expresses molecules of respiratory epithelium and resembles the epithelial thymic rudiment of nude mice.

The expression of tissue-specific Ags (TSA) within the thymic environment has emerged as an important contribution to the establishment of self-tolerance. The mechanistic basis for this property is poorly understood. One model has proposed stochastic derepression of gene expression by mature medullary epithelial cells, whereas another model has suggested that this property of thymic epithelial cells reflects transcriptional activity during their differentiation.

The absence of platelet-derived growth factor-B in circulating cells promotes immune and inflammatory responses in atherosclerosis-prone ApoE-/- mice.

Both innate and adaptive immunity contribute to the progression of inflammatory-fibrotic lesions of atherosclerosis. Although platelet-derived growth factor (PDGF)-B has been investigated as a stimulant of smooth muscle cells in vascular diseases, its effects on the immune response during disease have not been evaluated in vivo. We used hematopoietic chimeras generated after lethal irradiation of ApoE-/- recipients to test the role of PDGF in atherosclerosis.

Nude thymic rudiment lacking functional foxn1 resembles respiratory epithelium.

The epithelial compartment of the thymus arises from endoderm of the 3rd pharyngeal pouch. As it moves from a cervical to a mediastinal position during development, this epithelium becomes populated by lymphoid progenitor cells from the blood and begins to support their differentiation along the T cell lineage. Productive differentiation of thymic epithelium is strictly dependent on the foxn1 transcription factor, as evidenced by the lack of functional thymic tissue in nude mice that carry a spontaneous loss-of-function mutation of foxn1.

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.

Regulatory T cell lineage specification by the forkhead transcription factor foxp3.

Regulatory T cell-mediated dominant tolerance has been demonstrated to play an important role in the prevention of autoimmunity. Here, we present data arguing that the forkhead transcription factor Foxp3 acts as the regulatory T cell lineage specification factor and mediator of the genetic mechanism of dominant tolerance. We show that expression of Foxp3 is highly restricted to the subset alphabeta of T cells and, irrespective of CD25 expression, correlates with suppressor activity.

Cutting edge: TCR revision occurs in germinal centers.

Mouse CD4(+)Vbeta5(+) T cells recognize a peripherally expressed superantigen encoded by an endogenous retrovirus. Ag encounter tolerizes the mature CD4 T cell compartment, either by deletion of autoreactive cells or by TCR revision. This latter process is driven by TCRbeta rearrangement through RAG activity and results in the rescue of cells expressing novel TCRs that no longer recognize the tolerogen.