Biomedical subjects

Georg Kraal

Publications and source records attributed to Georg Kraal.

At least 19 recordsLinked to original sources

PubMed2006

Lipopolysaccharide-induced gene expression in murine macrophages is enhanced by prior exposure to oxLDL.

Uptake of modified lipoproteins by macrophages results in the formation of foam cells. We investigated how foam cell formation affects the inflammatory response of macrophages. Murine bone marrow-derived macrophages were treated with oxidized LDL (oxLDL) to induce foam cell formation. Subsequently, the foam cells were activated with lipopolysaccharide (LPS), and the expression of lipid metabolism and inflammatory genes was analyzed. Furthermore, gene expression profiles of foam cells were analyzed using a microarray. We found that prior exposure to oxLDL resulted in enhanced LPS-induced tumor necrosis factor (TNF) and interleukin-6 (IL-6) gene expression, whereas the expression of the anti-inflammatory cytokine IL-10 and interferon-beta was decreased in foam cells. Also, LPS-induced cytokine secretion of TNF, IL-6, and IL-12 was enhanced, whereas secretion of IL-10 was strongly reduced after oxLDL preincubation. Microarray experiments showed that the overall inflammatory response induced by LPS was enhanced by oxLDL loading of the macrophages. Moreover, oxLDL loading was shown to result in increased nuclear factor-kappaB activation. In conclusion, our experiments show that the inflammatory response to LPS is enhanced by loading of macrophages with oxLDL. These data demonstrate that foam cell formation may augment the inflammatory response of macrophages during atherogenesis, possibly in an IL-10-dependent manner.

Animals↗

PubMed2006

The antigen recognized by MOMA-I is sialoadhesin.

The monoclonal antibody MOMA-1 is a widely-used marker for marginal metallophilic macrophages in spleen and some other subsets of macrophages. The antigen recognized by MOMA-1 has yet to be characterized, but its expression pattern is similar to that of sialoadhesin (Sn, CD169, Siglec-1), a member of the sialic acid binding Ig-like lectin (Siglec) family. Using flow cytometry of Sn-transfected cells and staining of lymphoid tissue sections from Sn-deficient mice, we demonstrate here that the antigen recognized by MOMA-1 is Sn.

Animals↗

PubMed2006

MARCO, an innate activation marker of macrophages, is a class A scavenger receptor for Neisseria meningitidis.

The scavenger receptor-A I/II (SR-A) and macrophage receptor with collagenous domain (MARCO) share a common domain organisation and ligand repertoire, including selected polyanions and gram-positive and -negative organisms, but differ in fine specificity of ligand binding, tissue distribution and regulation. Neisseria meningitidis (NM) is a selective ligand for SR-A, but there is evidence for an additional SR-A-independent, polyanion-sensitive component for NM recognition. We therefore studied the relative contribution of MARCO and SR-A to binding of NM by resident and elicited peritoneal macrophages obtained from MARCO-/-, SR-A-/- and SR-A-MARCO-/- mice. Results confirmed that both mouse and human MARCO are able to bind NM independently of NM LPS. MARCO and SR-A contributed independently to NM binding, correlating with their expression levels in different cell populations, but neither of these two molecules was required for release of TNF-alpha and nitric oxide. We propose that the TLR-dependent induction of MARCO by innate immune stimulation enhances recognition and uptake of pathogenic organisms such as NM, thus contributing to host defence against infection.

Animals↗

PubMed2006

New insights into the cell biology of the marginal zone of the spleen.

In the marginal zone of the spleen the bloodstream passes through an open system of reticular cells and fibers in which various myeloid and lymphoid cells are located. Macrophages in this region are well equipped to recognize pathogens and filter the blood by virtue of unique combinations of pattern recognition receptors. They interact with a specific set of B cells that can be found only in the marginal zone and that are able to react rapidly to bacterial antigens in particular. This combination of strategically located cells is an important factor in our defense against blood-borne pathogens. New data on the development of the marginal zone itself and the marginal zone B cells are reviewed and discussed in light of the function of the spleen in host defense.

Animals↗

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

Defective microarchitecture of the spleen marginal zone and impaired response to a thymus-independent type 2 antigen in mice lacking scavenger receptors MARCO and SR-A.

The macrophage scavenger receptor macrophage receptor with a collagenous structure (MARCO) is expressed in mice by the marginal zone macrophages of the spleen and by macrophages of the medullary cords of lymph nodes, as well as the peritoneal macrophages. MARCO is a relative of scavenger receptor A (SR-A), the more widely expressed prototypic member of the scavenger receptor family. In the present study, we found that genetic ablation of MARCO leads to changes in the organization of the splenic marginal zone, and causes a significant reduction in the size of the resident peritoneal macrophage population, possibly due to changes in adhesion and migration capacity. In mice lacking both MARCO and SR-A these effects are even more apparent. During ontogeny, the appearance and organization of the MARCO-expressing cells in the spleen precedes the appearance of other receptors on macrophages in the marginal zone, such as SIGNR1 and Siglec-1. In the absence of MARCO, a clear delay in the organization of the marginal zone was observed. Similar findings were seen when the reappearance of the various subsets from precursors was studied after depleting macrophages from the adult spleen by a liposome treatment. When challenged with a pneumococcal polysaccharide vaccine, a T-independent type 2 Ag for which an intact marginal zone is crucial, the knockout mice exhibited a clearly impaired response. These findings suggest that both MARCO and SR-A, in addition to being important scavenger receptors, could be involved in the positioning and differentiation of macrophages, possibly through interaction with endogenous ligands.

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

Nuclear factor kappaB signaling in atherogenesis.

Atherosclerosis is an inflammatory disease, characterized by the accumulation of macrophage-derived foam cells in the vessel wall and accompanied by the production of a wide range of chemokines, cytokines, and growth factors. These factors regulate the turnover and differentiation of immigrating and resident cells, eventually influencing plaque development. One of the key regulators of inflammation is the transcription factor nuclear factor kappaB (NF-kappaB), which, for a long time, has been regarded as a proatherogenic factor, mainly because of its regulation of many of the proinflammatory genes linked to atherosclerosis. NF-kappaB may play an important role in guarding the delicate balance of the atherosclerotic process as a direct regulator of proinflammatory and anti-inflammatory genes and as a regulator of cell survival and proliferation. Here we address recent literature on the function of NF-kappaB in inflammatory responses and its relation to atherosclerosis.

Animals↗

PubMed2005

A function for the macrophage F4/80 molecule in tolerance induction.

The F4/80 monoclonal antibody has been used widely as a marker for mouse macrophages. The antigen (Ag) recognized by the antibody has been characterized as a member of the epidermal growth factor (EGF)-transmembrane 7 (TM7) family, although the function of the molecule has remained elusive. A recent study provides evidence for a role of the F4/80 molecule in the induction of immunological tolerance. This study appears to provide clear evidence for a role of the F4/80 molecule in the immune system, however, what does it really tell us about the activities of the F4/80 molecule?

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

Genetic analysis of macrophage characteristics as a tool to identify tumor susceptibility genes: mapping of three macrophage-associated risk inflammatory factors, marif1, marif2, and marif3.

Genetic predisposition to cancer is influenced by allelic variation in tumor susceptibility genes (TSGs) as present in the germline. We previously demonstrated in the mouse that TSGs frequently participate in genetic interactions, indicating that they represent molecular networks. Inflammation may constitute one of the molecular networks underlying susceptibility to cancer by influencing the tumor microenvironment. Because macrophages play a key role in inflammation and are often associated with tumors, we argue that a subset of TSGs can be identified by examining the genetics of macrophage characteristics. A panel of inflammation-related assays was established to phenotype mouse bone marrow-derived macrophages, which included stimulation with lipopolysaccharides followed by measurement of secretion of tumor necrosis factor alpha and the p40 chain of interleukin-12 and of expression of inducible nitric oxide synthase and cyclooxygenase-2. This panel of assays was used for linkage analysis and applied to bone marrow-derived macrophages derived from individual mice of segregating crosses between inbred strain O20 and the highly related strains NTX-10 and NTX-20, which differed from O20 in only 10% of their genome, to reduce genetic complexity. Three macrophage-associated risk inflammatory factors were mapped-Marif1, Marif2, and Marif3-that each affected several inflammation-related assays, confirming that they function within molecular networks. Moreover, Marif1 and Marif2 were localized in regions with established linkage for both quantitative and qualitative aspects of lung cancer susceptibility. These studies provide a novel approach to investigate the genetics of microenvironmental influence on predisposition to tumorigenesis, thereby contributing to development of new strategies that aim to prevent or treat cancer.

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

Early events in antigen-specific regulatory T cell induction via nasal and oral mucosa.

Mucosal Tr prevent harmful immune responses to innocuous antigens that are encountered at the mucosae. This unique subset of Tr is adaptive, antigen specific, and suppresses irrespective of cytokine polarization. Here we study the earliest events of mucosal Tr induction and factors that control their differentiation from naive T cells.

Administration, Oral↗

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↗