Biomedical subjects

Reina E Mebius

Publications and source records attributed to Reina E Mebius.

17 recordsLinked to original sources

PubMed2006

The importance of regional lymph nodes for mucosal tolerance.

The immune system is organized as a number of distinct lymphoid organs interconnected by recirculating lymphocytes. These organs, such as lymph nodes, spleen, and gut-associated Peyer's patches, are compartmentalized, providing separate niches for T and B cells. In addition, regional compartmentalization of lymphoid organs themselves exists, leading to the distinction between the mucosal and the systemic immune systems. This distinction not only reflects the anatomical localization but also is based on functional differences, with predominant tolerance induction via mucosal routes and immunity seen after systemic antigen exposure. These differences are associated with regional differences in the lymphoid organs and with environmental conditions of the tissues in which the immune system functions. Recirculation patterns of lymphocytes differ between mucosal and systemic lymphoid organs, and more insight into the mechanisms that imprint this behavior has been generated recently. Differences in dendritic cells have been observed between mucosal and systemic sites, and knowledge on how local factors contribute to the immune system is emerging. From our studies on mucosal tolerance in mouse models, it has become evident that regional lymph nodes draining the mucosa are important sites to direct immune responses. Here, we discuss the way regional lymph nodes contribute to the direction of immune responses and what is known about the local factors and cell behavior that form the basis for these differences.

Animals↗

PubMed2005

Fc gamma RIIB regulates nasal and oral tolerance: a role for dendritic cells.

Mucosal tolerance prevents the body from eliciting productive immune responses against harmless Ags that enter the body via the mucosae, and is mediated by the induction of regulatory T cells that differentiate in the mucosa-draining lymph nodes (LN) under defined conditions of Ag presentation. In this study, we show that mice deficient in FcgammaRIIB failed to develop mucosal tolerance to OVA, and demonstrate in vitro and in vivo a critical role for this receptor in modulating the Ag-presenting capacity of dendritic cells (DC). In vitro it was shown that absence of FcgammaRIIB under tolerogenic conditions led to increased IgG-induced release of inflammatory cytokines such as MCP-1, TNF-alpha, and IL-6 by bone marrow-derived DC, and increased their expression of costimulatory molecules, resulting in an altered immunogenic T cell response associated with increased IL-2 and IFN-gamma secretion. In vivo we could show enhanced LN-DC activation and increased numbers of Ag-specific IFN-gamma-producing T cells when FcgammaRIIB(-/-) mice were treated with OVA via the nasal mucosa, inferring that DC modulation by FcgammaRIIB directed the phenotype of the T cell response. Adoptive transfer of CD4(+) T cells from the spleen of FcgammaRIIB(-/-) mice to naive acceptor mice demonstrated that OVA-responding T cells failed to differentiate into regulatory T cells, explaining the lack of tolerance in these mice. Our findings demonstrate that signaling via FcgammaRIIB on DC, initiated by local IgG in the mucosa-draining LN, down-regulates DC activation induced by nasally applied Ag, resulting in those defined conditions of Ag presentation that lead to Tr induction and tolerance.

Administration, Intranasal↗

PubMed2005

Cellular interactions in lymph node development.

The organized accumulation of lymphocytes is a biological phenomenon used to optimize both homeostatic immune surveillance, as well as chronic responses to pathogenic stimuli. During embryonic development, circulating hemopoietic cells gather at predestined sites throughout the body, where they are subsequently arranged in T and B cell-specific areas characteristic of secondary lymphoid organs. In contrast, the body seems to harbor a limited second set of selected sites that support formation of organized lymphoid aggregates. However, these are only revealed at times of local, chronic inflammation, when so-called tertiary lymphoid structures appear. Once thought of as two distinct phenomena, recent insights suggest that highly similar networks of paracrine interactions regulate the formation of both secondary and tertiary lymphoid structures. This review will focus on these cellular interactions between organizing and inducing cell populations leading to the formation of lymph nodes or organized inflammatory infiltrates.

Animals↗

PubMed2005

Structure and function of the spleen.

The spleen combines the innate and adaptive immune system in a uniquely organized way. The structure of the spleen enables it to remove older erythrocytes from the circulation and leads to the efficient removal of blood-borne microorganisms and cellular debris. This function, in combination with a highly organized lymphoid compartment, makes the spleen the most important organ for antibacterial and antifungal immune reactivity. A better understanding of the function of this complex organ has been gained from recent studies, as outlined in this Review article.

Animals↗

PubMed2004

Initiation of cellular organization in lymph nodes is regulated by non-B cell-derived signals and is not dependent on CXC chemokine ligand 13.

The molecular and cellular events that initiate the formation of T and B cell areas in developing lymph nodes are poorly understood. In this study we show that formation of the lymphoid architecture in murine neonatal lymph nodes evolves through a series of distinct stages. The initial segregation of T and B cells is regulated in a CXCL13-independent manner, characterized by the localization of B cells in a ring-like pattern in the outer cortex on day 4. However, during this CXCL13-independent phase of lymph node modeling, CXCL13 is expressed and regulated in a lymphotoxin-alpha1beta2 (LTalpha1beta2)-dependent manner. Surprisingly, neonatal B cells are unable to respond to this chemokine and also lack surface LTalpha1beta2 expression. At this time, CD45+CD4+CD3- cells are the predominant LTalpha1beta2-expressing cells and are also capable of responding to CXCL13. From day 4 on, architectural changes become CXCL13 dependent, and B cells become fully CXCL13 responsive, express LTalpha1beta2, and cluster in anatomically distinct follicles. Because the initial induction of CXCL13 is dependent on LTalpha1beta2, a role for CD45+CD4+CD3- cells in inducing chemokine expression in the developing lymph nodes is proposed and, as such, a role in initiation of the shaping of the microenvironment.

Animals↗

PubMed2004

Presumptive lymph node organizers are differentially represented in developing mesenteric and peripheral nodes.

During murine embryogenesis, the formation of Peyer's patches (PPs) is initiated by CD45(+)CD4(+)CD3(-) lymphoid tissue inducers that trigger adhesion molecule expression and specific chemokine production from an organizing stromal cell population through ligation of the lymphotoxin-beta receptor. However, the steps involved in the development of lymph nodes (LNs) are less clear than those of PPs, and the characteristics of the organizing cells within the LN anlagen have yet to be documented. In this study, we show for the first time that the early anlage is bordered by an endothelial layer that retains a mixed lymphatic and blood vascular phenotype up to embryonic day 16.5. This in turn encompasses CD45(+)CD4(+)CD3(-) cells interspersed with ICAM-1/VCAM-1/mucosal addressin cell adhesion molecule-1, lymphotoxin-beta receptor-positive, chemokine-producing cells analogous to the organizing population previously observed in PPs. Moreover, these LN organizers also express the TNF family member, TRANCE. Lastly, we show that the ICAM-1/VCAM-1/mucosal addressin cell adhesion molecule-1 cells present in peripheral and mesenteric LN form two discrete populations expressing either intermediate or high levels of these adhesion molecules but that the former population is specifically reduced in PLN. These findings provide a possible explanation for the well-known differences in developmental requirements for nodes at peripheral or mesenteric locations.

Animals↗

PubMed2004

B cells are crucial for both development and maintenance of the splenic marginal zone.

The splenic marginal zone is a unique compartment that separates the lymphoid white pulp from the surrounding red pulp. Due to the orchestration of specialized macrophages and B cells flanking a marginal sinus, this compartment plays an important role in uptake of blood-borne Ags and it gives the spleen its specialized function in antibacterial immunity. In this study, we demonstrate that both development and maintenance of this marginal zone is highly dependent on the presence of B cells. Spleens from B cell-deficient mice were found to lack both metallophilic and marginal zone macrophages as well as mucosal addressin cellular adhesion molecule-1+ sinus lining cells. Using an inducible Cre/loxP-driven mouse model in which mature B cells could be partially depleted by removal of the B cell receptor subunit Igalpha, we could show that the integrity and function of an established marginal zone was also dependent on the presence of B cells. This was confirmed in a transgenic model in which all B cells were gradually depleted due to overexpression of the TNF family member CD70. The loss of all cellular subsets from the marginal zone in these CD70 transgenic mice was effectively prevented by crossing these mice on a CD27(-/-) or TCRalpha(-/-) background, because this prohibited the ongoing B cell depletion. Therefore, we conclude that B cells are not only important for the development, but also for maintenance, of the marginal zone. This direct correlation between circulating B cells and the function of the spleen implies an increased risk for B cell lymphopenic patients with bacterial infections.

Animals↗

PubMed2004

Effects of fluorescent and nonfluorescent tracing methods on lymphocyte migration in vivo.

BACKGROUND: The use of fluorescent dyes to monitor in vivo cellular migration and proliferation has greatly expanded, but little is known about their potential influence on cell migration. METHODS: Adoptive transfer studies of lymphocytes labeled with various dyes were performed, and their in vivo homing was compared with that of coinjected unlabeled control cells. In addition, in vitro migration and binding studies were performed to analyze the various steps of transmigration separately. RESULTS: These data showed that the intracellular fluorescent dyes calcein acetoxymethyl ester, 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester, 5-chloromethylfluorescein diacetate, 5-(and-6)-carboxyfluorescein diacetate, succinimidyl ester, and fluorescein isothiocyanate affect in vivo homing of especially B lymphocytes to lymphoid organs, without any direct effect on in vitro chemotactic or adhesive activity. The only label that did not affect migration was the extracellular and nonfluorescent molecule biotin, provided that the labeling was performed at room temperature. Interestingly, by using the highly versatile congenic Ly5.1-Ly5.2 system, we also demonstrated intrinsic differences in lymphocyte migration based on allelic differences. CONCLUSIONS: Our data showed that fluorescent labeling of lymphocytes has a severe effect on their homing capacity in vivo. Labeling of cells with biotin appeared to be a good alternative for this purpose; however, if direct fluorescence is required, the negative effects on cell migration should be considered.

Animals↗

PubMed2004

Induction of secondary and tertiary lymphoid structures in the skin.

During embryogenesis a developmental program leading to the formation of lymph nodes and Peyer's patches is initiated. We now show that lymph node-like structures as well as tertiary lymphoid structures can ectopically be induced by intradermal injection of newborn lymph node-derived cells. ICAM-1/VCAM-1-expressing stromal organizers, follicular dendritic cells, lymphatic endothelium, and HEVs in these structures are of donor origin, while all hematopoietic cells are host derived. Formation depends on lymphotoxin-expressing donor cells, whereas further organization requires lymphotoxin-expressing recipient cells. While induced secondary lymphoid structures develop a normal cellular architecture, the degree of organization in tertiary structures is correlated to the immune activation status of the host. These results indicate that the cellular and molecular requirements for the establishment of lymph nodes and tertiary structures are remarkably similar and that hyperactivated lymphocytes can fulfill the role of lymphoid tissue inducer cells during inflammatory responses.

Animals↗

PubMed2004

Development and function of the splenic marginal zone.

The marginal zone of the spleen is a crucial region where blood-borne pathogens are sequestered by macrophages with unique arrays of scavenger molecules. In addition, a special population of B cells, which is capable of rapid activation, resides in this region. Marginal zone B cells and macrophages together form an efficient interplay between innate and adaptive immunity. The developmental pathways that lead to the formation of the marginal zone are described, and the function of the marginal zone is discussed in relation to the function of the spleen as the major blood-filtering organ of the body.

Animals↗

PubMed2003

A conduit system distributes chemokines and small blood-borne molecules through the splenic white pulp.

Access to the splenic white pulp is restricted to lymphocytes and dendritic cells. Here we show that movement of molecules from the blood into these confined areas is also limited. Large molecules, such as bovine serum albumin (68 kD), immunoglobulin G (150 kD), and 500 kD dextran are unable to enter the white pulp, whereas smaller blood-borne molecules can directly permeate this compartment. The distribution is restricted to a stromal network that we refer to as the splenic conduit system. The small lumen of the conduit contains collagen fibers and is surrounded in the T cell areas by reticular fibroblasts that express ER-TR7. It also contains the chemokine CCL21. Conversely, in B cell follicles the B cell-attracting chemokine CXCL13 was found to be associated with the conduit and absence of ER-TR7+ fibroblasts. These results show heterogeneity of reticular fibroblasts that enfold the conduit system and suggest that locally produced chemokines are transported through and presented on this reticular network. Therefore, the conduit plays a role in distribution of both blood-borne and locally produced molecules and provides a framework for directing lymphocyte migration and organization of the splenic white pulp.

Animals↗

PubMed2003

Expression of the murine CD27 ligand CD70 in vitro and in vivo.

The interaction between TNFR family member CD27 and its ligand CD70 promotes lymphocyte expansion and effector cell formation. In humans, control of CD27 function is partly regulated by the restricted expression of CD70. We used newly developed mAbs to characterize murine (m) CD70 expression in vitro and in vivo. On resting lymphocytes and immature dendritic cells (DC), mCD70 is absent. In vitro, Ag receptor triggering induced mCD70 mRNA in T cells, but cell surface protein expression was very low. Activated B cells synthesized much higher levels of mCD70 mRNA than activated T cells and clearly expressed mCD70 at the cell surface. mCD70 cell surface expression could also be induced on the DC line D1 and on in vitro-generated murine DC upon maturation. In lymphoid organs of naive mice, virtually no mCD70-expressing cells were found, with exception of cells in the thymic medulla, which may be epithelial in origin. However, after intranasal infection with influenza virus, lung-infiltrating T cells and T and B cells in draining lymph nodes expressed mCD70 according to immunohistology. In such activated lymphocytes, mCD70 protein is largely retained intracellularly. Plasma membrane expression of mCD70 was only detectable by flow cytometry on a small proportion of lung-infiltrating T cells and peaked at the height of the primary response. Thus, expression of CD70 in the mouse is highly regulated at the transcriptional and posttranslational level. This most likely serves to limit excessive effector cell formation after antigenic stimulation.

Animals↗

PubMed2003

Role of chemokines in the development of secondary and tertiary lymphoid tissues.

Organogenesis of lymph nodes and Peyer's patches is initiated during embryonic development and depends on the correct expression of a wide variety of molecules. Essential for this process is the paracrine triggering of stromal cells by CD45+CD4+CD3- cells. Hereto CD45+CD4+CD3- cells and stromal cells need to be spatially positioned in close proximity to each other. Expression of adhesion molecules and chemokines is thought to be essential for this process. During adult life, similar processes might also be at the basis of development of organized tertiary lymphoid structures often seen in inflammatory lesions.

Animals↗

PubMed2003

Organogenesis of lymphoid tissues.

The development of lymphoid organs depends on the correct expression of several molecules within a defined timeframe during ontogeny. Although this is an extremely complex process, with each secondary lymphoid tissue requiring subtly different signals, a common framework for lymphoid development is beginning to emerge. Drawing on studies of lymph nodes, Peyer's patches and nasal-associated lymphoid tissue, an integrative model of lymphoid-tissue development, involving adhesion molecules, cytokines and chemokines, which emphasizes the role of interactions between CD3-CD4+CD45+ 'inducer' cells and VCAM1+ICAM1+ stromal 'organizer' cells is presented.

Animals↗

PubMed2002

The role of CD45+CD4+CD3- cells in lymphoid organ development.

In the last 10 years the continuing search for gene function has yielded many mutant mice that unexpectedly showed a complete lack of lymph nodes and/or Peyer's patches. With the realization that all these functionally highly diverse genes are involved at some point in the development of lymphoid organs, the challenge now is to assign a function to the molecules involved in lymphoid organ development. It will be important to determine the sequence of molecular events and assign this to the cellular events that lead to an accumulation of hematopoietic cells in one location, ultimately forming an organized lymphoid organ. Here we will focus on CD45+CD4+CD3- cells that are the early colonizing cells in lymph nodes and Peyer's patches and develop a hypothetical model of their contribution to the creation of organized lymphoid structures.

Animals↗

PubMed2002

The strict regulation of lymphocyte migration to splenic white pulp does not involve common homing receptors.

Although the spleen is the largest secondary lymphoid organ, little is known about the regulation of lymphocyte migration towards its different compartments of red and white pulp, in contrast to the well-studied mechanisms of lymphocyte homing to lymph nodes. Here we show that short-term trypsin treatment of lymphocytes cleaved off molecules involved in entry into lymph nodes, while homing to the splenic white pulp was unaltered. Prolonged trypsin treatment also abolished the ability of lymphocytes to enter the white pulp. Analysis of affected cell surface molecules and adoptive transfer studies in combination with blocking antibodies revealed that l-selectin, CD44, PSGL-1 and the alpha4 integrins are not required for migration to the white pulp. Although lymphocyte function-associated antigen-1 (LFA-1) is critical for entry into lymph nodes, we show here that in the absence of functional LFA-1 molecules, lymphocytes can still enter the white pulp, in spite of the high expression of intercellular adhesion molecule-1 on sinus lining cells in the marginal zone. The data indicate that adhesion molecules involved in lymphocyte homing to lymph nodes are not essential for migration towards the splenic white pulp, but that additional, trypsin-sensitive, and so far unidentified, molecules are required.

Adoptive Transfer↗

PubMed2002

Arginine deficiency affects early B cell maturation and lymphoid organ development in transgenic mice.

Apart from its role in the synthesis of protein and nitric oxide (NO), and in ammonia detoxification, the amino acid arginine exerts an immunosupportive function. We have studied the role of arginine in immune defense mechanisms in the developing postnatal immune system. In suckling mice, arginine is produced in the small intestine. In F/A-2(+/+) transgenic mice, which overexpress arginase in their enterocytes, circulating and tissue arginine concentrations are reduced to 30-35% of controls. In these mice, the development and composition of the T cell compartment did not reveal abnormalities. However, in peripheral lymphoid organs and the small intestine, B cell cellularity and the number and size of Peyer's patches were drastically reduced, and serum IgM levels were significantly decreased. These phenotypes could be traced to an impaired transition from the pro- to pre-B cell stage in the bone marrow. Cytokine receptor levels in the bone marrow were normal. The development of the few peripheral B cells and their proliferative response after in vitro stimulation was normal. The disturbance in B cell maturation was dependent on decreased arginine levels, as this phenotype disappeared upon arginine supplementation and was not seen in NO synthase- or ornithine transcarbamoylase-deficient mice. We conclude that arginine deficiency impairs early B cell maturation.

Animals↗