How to find your way through the thymus: a practical guide for aspiring T cells

Thymocytes must complete an elaborate developmental program in the thymus to ultimately generate T cells that express functional but neither harmful nor useless TCRs. Each developmental step coincides with dynamic relocation of the thymocytes between anatomically discrete thymic microenvironments, suggesting that thymocytes’ migration is tightly regulated by their developmental status. Chemokines produced by thymic stromal cells and chemokine receptors on the thymocytes play an indispensable role in guiding developing thymocytes into the different microenvironments. In addition to long-range migration, chemokines increase the thymocytes’ motility, enhancing their interaction with stromal cells. During the past several years, much progress has been made to determine the various signals that guide thymocytes on their journey within the thymus. In this review, we summarize the progress in identifying chemokines and other chemoattractant signals that direct intrathymic migration. Furthermore, we discuss the recent advances of two-photon microscopy in determining dynamic motility and interaction behavior of thymocytes within distinct compartments to provide a better understanding of the relationship between thymocyte motility and development.     

Basement membrane components are key players in specialized extracellular matrices

More than three decades ago, basement membranes (BMs) were described as membrane-like structures capable of isolating a cell from and connecting a cell to its environment. Since this time, it has been revealed that BMs are specialized extracellular matrices (sECMs) with unique components that support important functions including differentiation, proliferation, migration, and chemotaxis of cells during development. The composition of these sECM is as unique as the tissues to which they are localized, opening the possibility that such matrices can fulfill distinct functions. Changes in BM composition play significant roles in facilitating the development of various diseases. Furthermore, tissues have to provide sECM for their stem cells during development and for their adult life. Here, we briefly review the latest research on these unique sECM and their components with a special emphasis on embryonic and adult stem cells and their niches.     

The influence of sodium-8-chlorotheophyllinate (S8CT) on immune processes

Summary S8CT injected at the time of immunization significantly enhances specific IgM-production but has no effect on IgG-formation. Mitogen (PHA-P) induced macrophage migration inhibition of cells of S8CT pretreated animals is reduced. The same effect is observed, when normal cells are tested in the presence of S8CT in vitro. Blast transformation of B-lymphocytes but not of thymocytes is significantly stimulated by S8CT. Acid phosphatase activity is also stimulated in B-cells and- to a lesser degree-in cortisone-resistant T-lymphocytes whereas the activity of the total thymocyte population is reduced. No effect was seen on phagocytosis and intracellular bactericidal activity. A stimulatory effect of S8CT for B-cells is postulated.Presented in part at the Xth International Congress of Allergology and Clinical Immunology, Jerusalem/Israel 1979, Nov. 4–11.     

Antigenic correlation between rat thymus and superior cervical ganglion.

By using rabbit anti-rat thymocyte and anti-rat superior cervical ganglion sera in cytotoxicity, immunofluorescence and absorption assays, it has been shown that surface membranes of rat thymocytes and cervical ganglion cells (i.e. peripheral nervous tissue cells) contain common antigenic determinants.     

Germline development in vertebrates and invertebrates

In all animals information is passed from parent to offspring via the germline, which segregates from the soma early in development and undergoes a complex developmental program to give rise to the adult gametes. Many aspects of germline development have been conserved throughout the animal kingdom. Here we review the unique properties of germ cells, the initial determination of germ cell fates, the maintenance of germ cell identity, the migration of germ cells to the somatic gonadal primordia and the proliferation of germ cells during development in vertebrates and invertebrates. Similarities in germline development in such diverse organisms as Drosophila melanogaster, Caenorhabditis elegans, Xenopus laevis and Mus musculus will be highlighted. Received 11 December 1998; received after revision 25 January 1999; accepted 25 January 1999     

Dual Vα T cells

The assumption that T cells can only express a single receptor for antigen has in recent years been shown to be incorrect. However, the finding that a substantial number of T cells express two distinct antigen receptors at the cell surface raises a number of questions. In particular, it has been suggested that cells expressing low levels of a self-reactive T cell receptor may escape self-tolerance mechanisms and in certain situations trigger the onset of autoimmune disease. Such a hypothesis in turn raises questions central to the understanding of the nature of T cell recognition and the process of thymocyte maturation.     

Antigenic correlation between rat thymus and superior cervical ganglion

Summary By using rabbit anti-rat thymocyte and anti-rat superior cervical ganglion sera in cytotoxicity, immunofluorescence and absorption assays, it has been shown that surface membranes of rat thymocytes and cervical ganglion cells (i.e. peripheral nervous tissue cells) contain common antigenic determinants.Acknowledgment. This work was supported by grants from the Republic Research Fund of Serbia, Belgrade.     

Molecular and cellular mechanisms of T Cell development

The thymus is central to the establishment of a functioning immune system. Here is the place where T cells mature from hematopoietic progenitors, driven by mutual interactions of stromal cells and the developing thymocytes. As a result, different types of T cells are generated, all of which have been carefully selected for the ability to act in host defense towards non-self and against the potential to mount pathogenic self-reactive autoimmune responses. In this review we summarize our present knowlege on the lineage decisions taking place during this development, the selection processes responsible for shaping the T cell antigen-receptor repertoire, the interactions with the stromal components and the signal transduction pathways which transform the interactions with the thymic microenvironment into cellular responses of survival, proliferation, differentiation and, importantly, also of cell death. Received 12 June 2003; received after revision 22 July 2003; accepted 28 July 2003     

Glucocorticoids in T cell apoptosis and function

Glucocorticoids (GCs) are a class of steroid hormones which regulate a variety of essential biological functions. The profound anti-inflammatory and immunosuppressive activity of synthetic GCs, combined with their power to induce lymphocyte apoptosis place them among the most commonly prescribed drugs worldwide. Endogenous GCs also exert a wide range of immunomodulatory activities, including the control of T cell homeostasis. Most, if not all of these effects are mediated through the glucocorticoid receptor, a member of the nuclear receptor superfamily. However, the signaling pathways and their cell type specificity remain poorly defined. In this review, we summarize our present knowledge on GC action, the mechanisms employed to induce apoptosis and the currently discussed models of how they may participate in thymocyte development. Although our knowledge in this field has substantially increased during recent years, we are still far from a comprehensive picture of the role that GCs play in T lymphocytes. Received 20 August 2005; received after revision 27 September 2005; accepted 10 October 2005     

Use of aggregating cell cultures for toxicological studies

Relatively simple techniques are now available which allow the preparation of large quantities of highly reproducible aggregate cultures from fetal rat brain or liver cells, and to grow them in a chemically defined medium. Since these cultures exhibit extensive histotypic cellular reorganization and maturation, they offer unique possibilities for developmental studies. Therefore, the purpose of the present study was to investigate the usefulness of these cultures in developmental toxicology. Aggregating brain cell cultures were exposed at different developmental stages to model drugs (i.e., antimitotic, neurotoxic, and teratogenic agents) and assayed for their responsiveness by measuring a set of biochemical parameters (i.e., total protein and DNA content, cell type-specific enzyme activities) which permit a monitoring of cellular growth and maturation. It was found that each test compound elicited a distinct, dose-dependent response pattern, which may ultimately serve to screen and classify toxic drugs by using mechanistic criteria. In addition, it could be shown that aggregating liver cell cultures are capable of toxic drug activation, and that they can be used in co-culture with brain cell aggregates, providing a potential model for complementary toxicological and metabolic studies.     

Opposing effects on the cell cycle of T lymphocytes by Fbxo7 via Cdk6 and p27

G₁ phase cell cycle proteins, such as cyclin-dependent kinase 6 (Cdk6) and its activating partners, the D-type cyclins, are important regulators of T-cell development and function. An F-box protein, called F-box only protein 7 (Fbxo7), acts as a cell cycle regulator by enhancing cyclin D-Cdk6 complex formation and stabilising levels of p27, a cyclin-dependent kinase inhibitor. We generated a murine model of reduced Fbxo7 expression to test its physiological role in multiple tissues and found that these mice displayed a pronounced thymic hypoplasia. Further analysis revealed that Fbxo7 differentially affected proliferation and apoptosis of thymocytes at various stages of differentiation in the thymus and also mature T-cell function and proliferation in the periphery. Paradoxically, Fbxo7-deficient immature thymocytes failed to undergo expansion in the thymus due to a lack of Cdk6 activity, while mature T cells showed enhanced proliferative capacity upon T-cell receptor engagement due to reduced p27 levels. Our studies reveal differential cell cycle regulation by Fbxo7 at different stages in T-cell development.     

Use of aggregating cell cultures for toxicological studies

Summary Relatively simple techniques are now available which allow the preparation of large quantities of highly reproducible aggregate cultures from fetal rat brain or liver cells, and to grow them in a chemically defined medium. Since these cultures exhibit extensive histotypic cellular reorganization and maturation, they offer unique possibilities for developmental studies. Therefore, the purpose of the present study was to investigate the usefulness of these cultures in developmental toxicology. Aggregating brain cell cultures were exposed at different developmental stages to model drugs (i.e., antimitotic, neurotoxic, and teratogenic agents) and assayed for their responsiveness by measuring a set of biochemical parameters (i.e., total protein and DNA content, cell type-specific enzyme activities) which permit a monitoring of cellular growth and maturation. It was found that each test compound elicited a distinct, dose-dependent response pattern, which may ultimately serve to screen and classify toxic drugs by using mechanistic criteria. In addition, it could be shown that aggregating liver cell cultures are capable of toxic drug activation, and that they can be used in co-culture with brain cell aggregates, providing a potential model for complementary toxicological and metabolic studies.     

The obesity-related pathology and Th17 cells

Chronic inflammation associated with obesity plays a major role in the development of metabolic diseases, cancer, and autoimmune diseases. Among Th subsets, Th17 cells are involved in the pathogenesis of autoimmune disorders such as psoriasis, rheumatoid arthritis, inflammatory bowel disease, steroid-resistant asthma, and multiple sclerosis. Accumulating data suggest that reciprocal interactions between the metabolic systems and immune system play pivotal roles in the pathogenesis of obesity-associated diseases. We herein outline the developing principles in the control of T cell differentiation and function via their cellular metabolism. Also discussed are recent findings that changes in the intracellular metabolism, including fatty acid metabolism, affect the Th17 cell function in obese individuals. Finally, we will also highlight the unique molecular mechanism involved in the activation of retinoid-related orphan receptor-gamma-t (RORγt) by intracellular metabolism and discuss a new therapeutic approach for treating autoimmune disorders through the inhibition of RORγt.     

Mitochondria dynamism: of shape,transport and cell migration

Mitochondria are highly dynamic and functionally versatile organelles that continuously fragment and fuse in response to different physiological needs of the cell. The list of proteins that strictly regulate the morphology of these organelles is constantly growing, adding new players every day and new pieces to the comprehension and elucidation of this complex machinery. The structural complexity of mitochondria is only paralled by their functional versatility. Indeed, changes in mitochondria shape play critical roles in vertebrate development programmed cell death and in various processes of normal cell physiology, such as calcium signaling, reactive oxygen species production, and lifespan. Here, we present the latest findings on the regulation of mitochondrial dynamics and some of their physiological roles, focusing on cell migration. In cells where migration represents a crucial function in their physiology, such as T and tumoral metastatic cells, mitochondria need to be fragmented and recruited to specific subcellular regions to make movement possible. In depth analysis of this role of mitochondrial dynamics should help in identifying potential targeted therapy against cancer or in improving the immune system’s efficiency.     

Receptor communication within the lymphocyte plasma membrane: a role for the thrombospondin family of matricellular proteins

Lymphocytes, the principal cells of the immune system, carry out immune surveillance throughout the body by their unique capacity to constantly reposition themselves between a free-floating vascular state and a tissue state characterized by migration and frequent adhesive interactions with endothelial cells and components of the extracellular matrix. Therefore, mechanisms co-ordinating adhesion and migration with signals delivered through antigen recognition probably play a pivotal role for the regulation of lymphocyte behaviour and function. Endogenous thrombospondin-1 (TSP-1) seems to be the hub in such a mechanism for autocrine regulation of T cell adhesion and migration. TSP-1 functions as a mediator of cis interaction of vital receptors within the T lymphocyte plasma membrane, including integrins, low density lipoprotein receptor-related protein, calreticulin and integrin-associated protein. Received 1 June 2006; received after revision 28 June 2006; accepted 11 October 2006     

Analysis of the immune system with transgenic mice: T cell development

Transgenic mice carrying functionally rearranged T cell receptor genes have contributed significantly to our knowledge of T cell development and thymic positive and negative selection processes. In addition, TCR-transgenic mice have been used to investigate mutations affecting thymocyte development, like scid and lpr. Gene targeting by homologous recombination will allow to analyze more specifically the molecular mechanisms underlying thymic selection and peripheral tolerance.     

Common Molecular Mechanisms of Mammary Gland Development and Breast Cancer

The mammary gland undergoes major developmental changes during puberty and pregnancy. It is thought that stem cells drive mammary gland development during puberty and are responsible for tissue maintenance as well as the major growth and remodelling that occurs with every pregnancy. The use of sophisticated cell separation procedures has facilitated the prospective isolation of mammary epithelial stem and differentiated cell subpopulations from the mouse mammary gland, while studies of primary human breast cancers have described sub-populations of tumourigenic cells capable of initiating tumour growth in immuno-compromised mice. These potential tumour 'stem cells' constitute an important therapeutic target population with respect to cancer therapy, as these are likely to be the cells which maintain tumour growth. Understanding the origin of these cells, their relationship to breast cancer subtypes, and how and why they differ from normal breast stem cells will lead to a revolution in tumour understanding, treatment and prevention. (Part of a Multi-author Review).     

Analysis of the immune system with transgenic mice: T cell development

Transgenic mice carrying functionally rearranged T cell receptor genes have contributed significantly to our knowledge of T cell development and thymic positive and negative selection processes. In addition, TCR-transgenic mice have been used to investigate mutations affecting thymocyte development, likescid andlpr. Gene targeting by homologous recombination will allow to analyze more specifically the molecular mechanisms underlying thymic selection and peripheral tolerance.     

Tetraspanin-enriched microdomains regulate digitation junctions

Tetraspanins co-emerged with multi-cellular organisms during evolution are typically localized at the cell–cell interface, and form tetraspanin-enriched microdomains (TEMs) by associating with each other and other membrane molecules. Tetraspanins affect various biological functions, but how tetraspanins engage in multi-faceted functions at the cellular level is largely unknown. When cells interact, the membrane microextrusions at the cell–cell interfaces form dynamic, digit-like structures between cells, which we term digitation junctions (DJs). We found that (1) tetraspanins CD9, CD81, and CD82 and (2) TEM-associated molecules integrin α3β1, CD44, EWI2/PGRL, and PI-4P are present in DJs of epithelial, endothelial, and cancer cells. Tetraspanins and their associated molecules also regulate the formation and development of DJs. Moreover, (1) actin cytoskeleton, RhoA, and actomyosin activities and (2) growth factor receptor-Src-MAP kinase signaling, but not PI-3 kinase, regulate DJs. Finally, we showed that DJs consist of various forms in different cells. Thus, DJs are common, interactive structures between cells, and likely affect cell adhesion, migration, and communication. TEMs probably modulate various cell functions through DJs. Our findings highlight that DJ morphogenesis reflects the transition between cell–matrix adhesion and cell–cell adhesion and involves both cell–cell and cell–matrix adhesion molecules.