Organized Lymphoid Structures Research Articles

Blocking lymphotoxin-beta receptor activation diminishes inflammation via reduced mucosal addressin cell adhesion molecule-1 (MAdCAM-1) expression and leucocyte margination in chronic DSS-induced colitis.

The lymphotoxin-beta receptor (LTbetaR) pathway is critical for maintenance of organized lymphoid structures and is involved in the development of colitis. To investigate the mechanisms by which LTbetaR activation contributes to the pathology of chronic inflammation we used a soluble LTbetaR-Ig fusion protein as a competitive inhibitor of LTbetaR activation in the mouse model of chronic colitis induced by oral administration of dextran sulphate sodium. Strong expression of LTbeta which constitutes part of the LTalpha(1)beta(2) ligand complex was detected in colonic tissue of mice with chronic colitis. Treatment with LTbetaR-Ig significantly attenuated the development and histological manifestations of the chronic inflammation and reduced the production of inflammatory cytokines such as TNF, IL-1beta, and IL-6. Moreover, LTbetaR-Ig treatment significantly down-regulated mucosal addressin cell adhesion molecule-1 (MAdCAM-1) expression, leading to reduced leucocyte rolling and sticking in postcapillary and collecting venules and reduced extravasation into the intestinal mucosa as quantified by in vivo fluorescence microscopy. Thus, LTbetaR pathway inhibition ameliorates DSS-induced experimental chronic colitis in mice by MAdCAM-1 down-regulation entailing reduced lymphocyte margination and extravasation into the inflamed mucosa. Therefore, a combined treatment with reagents blocking T cell-mediated perpetuation of chronic inflammation such as LTbetaR-Ig together with direct anti-inflammatory reagents such as TNF inhibitors could constitute a promising treatment strategy for chronic colitis.

NALT-genesis is induced by Id2 gene-dependent CD3 −CD4 +CD45 + cells

CD3 −CD4 +CD45 + cells are thought to be an inducer cell population for Peyer's patch (PP) and lymph node development. Nasopharyngeal-associated lymphoid tissue (NALT) is an organized lymphoid structure found on both sides of the nasopharyngeal duct dorsal to the cartilaginous soft palate. Although NALT is considered to be functionally analogous to PP in the intestinal tract, the association of CD3 −CD4 +CD45 + cells with the initiation of NALT development has not yet been clarified. To examine this issue further, we isolated CD3 −CD4 +CD45 + cells from the fetal intestines of wild-type mice. Id2 −/− mice genetically deficient in NALT were adoptively transferred with purified CD3 −CD4 +CD45 + cells or fetal liver cells. After the adoptive transfer, we employed immunohistochemical analysis to examine the expression of PNAd, an important addressin for the recruitment of lymphocytes, in the nasal tissue of Id2 −/− mice transferred with fetal liver cells. Though NALT-like structures were indeed induced in Id2 −/− mice adoptively transferred with CD3 −CD4 +CD45 + cells or fetal liver cells, those structures were not observed to express PNAd. These findings indicate that CD3 −CD4 +CD45 + cells and Id2 genes are key to the initiation of NALT. However, they also suggest that an additional element is required for the induction of PNAd.

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.

Regulation of secondary lymphoid organ development by the nuclear factor-kappaB signal transduction pathway.

In primary lymphoid organs, such as thymus and bone marrow, B and T lymphocytes differentiate from lymphoid stem cells into mature albeit naïve effector cells. In contrast, secondary lymphoid organs, such as the spleen, lymph nodes, and Peyer's patches (PPs), provide an environment that enable lymphocytes to interact with each other, with accessory cells, and with antigens, resulting in the initiation of antigen-specific primary immune responses. Recently, the analysis of gene-knockout mice has shed light on the signaling pathways, cellular requirements, and molecular mechanisms involved in secondary lymphoid organ development. In particular, signals that converge on the nuclear factor-kappaB (NF-kappaB) pathway have been demonstrated to play an important role in both early developmental steps as well as maintenance of secondary lymphoid organ structures. Analysis of the histopathological changes in secondary lymphoid tissues of mice lacking individual Rel/NF-kappaB family members, upstream kinases, and receptors strongly indicates that activation of the recently described alternative NF-kappaB pathway by membrane-bound lymphotoxin, via p52-RelB heterodimers, plays a major role during initiation steps of secondary lymphoid organ development. Induction of the classical p50-RelA NF-kappaB activity, as exemplified by tumor necrosis factor receptor signaling, clearly also contributes, but seems to be involved primarily in later developmental step, such as the proper cellular and structural organization of B-cell follicles.

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.

Dendritic cells, chemokine receptors and autoimmune inflammatory diseases.

Dendritic cells (DC) have been implicated in the induction of autoimmune diseases and have been identified in lesions associated with several autoimmune inflammatory diseases. Since DC are regarded as the professional antigen-presenting cell (APC) of the immune system and the only APC capable of activating naïve T cells, they are likely to play a significant role in breaking tolerance of self-reactive lymphocytes and in supporting autoimmune responses in these diseases. A number of studies have revealed that small molecular weight chemotactic proteins known as chemokines are present within the autoimmune lesions and may contribute to the recruitment not only of DC populations, but also of immune cells such as T cells, B cells, neutrophils and monocytes into the site, and to the formation of organized lymphoid tissue structures within the target organ. The focus of this review will be a discussion of the role of chemokines in the recruitment of DC in human autoimmune inflammatory disorders, specifically the trafficking of DC into the inflammatory sites and the subsequent migration of differentiated DC from the inflammatory sites into the draining lymph nodes. Once DC are properly positioned within the lymph nodes, circulating antigen specific naïve T cells can interact with DC and become activated, clonally expanded and stimulated to undergo differentiation into antigen-experienced memory T cells. Subsequent reactivation of memory T cells that enter the autoimmune lesions by DC present in the inflammatory lesion is thought to play a central role in tissue inflammation.

Evolution of classic Hodgkin lymphoma in correlation to changes in the lymphoid organ structure of vertebrates

In order to integrate evolutionary concepts into lymphoma research we mapped features of classic Hodgkin lymphoma (a disease which has been recently described to be derived from germinal center B-cells) onto a phylogenetic tree of vertebrates. Secondly, we matched the phylogenetic occurrence of classic Hodgkin lymphoma to the changes in the lymphoid organ structure during vertebrate evolution. According to our analysis, classic Hodgkin lymphoma evolved exclusively at the developmental stage of mammals. Interestingly the appearance of Hodgkin lymphoma is correlated to the evolution of germinal centers in mammals. This lends some credit to the hypothesis that genes specific to the germinal center reaction are involved in the pathogenesis of Hodgkin lymphoma. However, as evolution did not stop at the developmental stage of the mammalian stem-species, to a certain extent species with specific differences of classic Hodgkin lymphoma can be expected. One such difference is that classic Hodgkin lymphoma occurs with a significantly higher frequency in humans than in all other mammals. This could be partially due to Epstein–Barr virus (EBV) infection in approximately 40%–50% of Hodgkin disease cases, that is associated with an expression of the EBV-encoded oncogen LMP-1. In conclusion we propose that the mapping of lymphoma related characteristics onto a phylogenetic tree is a valuable new tool in lymphoma research.

Recall and propagation of allospecific memory T cells independent of secondary lymphoid organs.

The allospecifc T cell population responding to a transplanted organ consists of both naive and memory lymphocytes. Although it is established that naive T cells are activated by antigen within the organized structures of secondary lymphoid organs (the spleen, lymph nodes, and mucosal lymphoid tissues), it is not clear whether memory T cell activation and propagation depend on homing to these organs. To answer this question, we investigated whether allospecific naive or memory T cells can mediate acute cardiac allograft rejection in mutant mice that lack all of their secondary lymphoid tissues. The results of our experiments demonstrated that antigen-experienced memory T cells have two advantages over naive T cells: (i) memory T cells mount a vigorous immune response that leads to allograft rejection independent of secondary lymphoid organs; and (ii) memory T cells generate more memory T cells without homing to secondary lymphoid organs. These unique properties of memory T cells were further confirmed by showing that memory-like T cells that arise from the homeostatic proliferation of naive T cells in the absence of antigenic stimulation are suboptimal at rejecting allografts and do not generate memory T cells in mice devoid of secondary lymphoid tissues.

Geertruida Jeanette Thorbecke (1929–2001)

Geertruida Jeanette Thorbecke (1929–2001)

The molecular basis of lymphoid architecture and B cell responses: implications for immunodeficiency and immunopathology.

Immune responses usually take place in secondary lymphoid organs such as spleen and lymph nodes. Most lymphocytes within these organs are in transit, yet lymphoid organ structure is highly organized; T and B cells segregate into separate regions. B cell compartments include naïve cells within follicles, marginal zones and B-1 cells. Interactions between TNF family molecules on hematopoietic cells and their receptors on mesenchymal cells guide the initial phase of lymphoid organogenesis, and regulate chemokine secretion that mediates subsequent T-B cell segregation. Recruitment of B cells into different compartments depends on both the milieu established during organogenesis, and the threshold for B cell receptor signaling, which is modulated by numerous coreceptors. Novel intrafollicular (germinal center) and extrafollicular (plasma cell) compartments are established when B cells respond to antigen. These divergent B cell responses are mediated by different patterns of gene expression, and influenced again by BCR signaling threshold and cellular interactions that depend on normal lymphoid architecture. Aberrant B cell responses are reviewed in the light of these principles taking into account the molecular and architectural aspects of immunopathology. Histological features of immunodeficiency reflect defects of B cell recruitment or differentiation. B cell hyper-reactivity may arise from altered BCR signaling thresholds (autoimmunity), defects in stimuli that guide differentiation in response to antigen (follicular hyperplasia vs plasmacytosis), or defective B cell gene expression. Interestingly, in diseases such as rheumatoid arthritis, Sjogren's syndrome and Hashimoto's thyroiditis lymphoid organogenesis may be recapitulated in non-lymphoid parenchyma, under the influence of molecular interactions similar to those that operate during embryogenesis.

Membrane-Bound TNF Supports Secondary Lymphoid Organ Structure but Is Subservient to Secreted TNF in Driving Autoimmune Inflammation

Mice without secreted TNF but with functional, normally regulated and expressed membrane-bound TNF (memTNF Δ/Δ mice) were created by knocking-in the uncleavable Δ1-9,K11E TNF allele. In contrast to TNF-deficient mice (TNF −/−), memTNF supported many features of lymphoid organ structure, except generation of primary B cell follicles. Splenic chemokine expression was near normal. MemTNF-induced apoptosis was mediated through both TNF-R1 and TNF-R2. That memTNF is suboptimal for development of inflammation was revealed in experimental autoimmune encephalomyelitis. Disease severity was reduced in memTNF Δ/Δ mice relative to wild-type mice, and the nature of spinal cord infiltrates resembled that in TNF −/− mice. We conclude that memTNF supports many processes underlying lymphoid tissue structure, but secreted TNF is needed for optimal inflammatory lesion development.

Blocking lymphotoxin: a potential therapy for diabetes?

Nonobese diabetic (NOD) mice spontaneously develop autoimmune diabetes, bearing close resemblance to the human condition. The disease is mediated by auto-specific T cells, which infiltrate the pancreatic islets and destroy insulin-producing β cells. A hallmark of the disease is the de novo generation of lymph-node-like structures in the pancreas, which are essential for progression of the disease. A large body of evidence implicates lymphotoxin (LT) in the formation of these lymphoid structures and the production of follicular dendritic cells. In support of this notion, the ectopic expression of LT can result in the in situ generation of lymph-node-like organs in the periphery. Hence, it was supposed that the formation of organized lymphoid structures in the pancreas of NOD mice might be regulated by LT.

HIV-specific effector cytotoxic T lymphocytes and HIV-producing cells colocalize in white pulps and germinal centers from infected patients

AbstractHuman immunodeficiency virus (HIV) infection is characterized by the massive infiltration of secondary lymphoid organs with activated CD8+ T lymphocytes. While converging data indicated that these cells were HIV-specific cytotoxic T lymphocytes (CTLs) responsible for HIV spread limitation, direct evidence was lacking. Here, the presence of HIV-specific effector CTLs was demonstrated directly ex vivo in 15 of 24 microdissected splenic white pulps from an untreated patient and in 1 of 24 tonsil germinal centers from a second patient with incomplete viral suppression following bitherapy. These patients had plasma HIV RNA loads of 5900 and 820 copies per milliliter. The frequencies of HIV-1 DNA+ cells in their lymphoid organs were more than 1 in 50 and 1 in 175, respectively. Spliced viral messenger RNA (a marker for ongoing viral replication) was present in most immunocompetent structures tested. Conversely, CTL activity was not found in spleens from 2 patients under highly active antiretroviral therapy, with undetectable plasma viral load. These patients had much lower spleen DNA+ cell frequencies (1 in 2700 and 1 in 3800) and no white pulps containing spliced RNA. CTL effector activity as well as spliced viral messenger RNA were both concentrated in the white pulps and germinal centers. This colocalization indicates that viral replication in immunocompetent structures of secondary lymphoid organs triggers anti-HIV effector CTLs to these particular locations, providing clues to target therapeutic intervention.

"Lymphoid" chemokine messenger RNA expression by epithelial cells in the chronic inflammatory lesion of the salivary glands of Sjögren's syndrome patients: possible participation in lymphoid structure formation.

Many studies have shown that the microanatomic organization of infiltrating leukocytes in the salivary gland lesions of patients with Sjögren's syndrome (SS) resembles the structure of lymphoid organs. A newly defined set of chemokines referred to as "lymphoid," which orchestrate leukocyte microenvironmental homing and contribute to the formation of lymphoid structures, provides directional clues. The aim of this study was to investigate the possible existence of "lymphoid" chemokines in the chronic inflammatory lesions of SS patients and thus validate their potential involvement in the disease process. Twelve patients with primary SS, 3 patients with secondary SS, 4 patients with other autoimmune disorders, and 4 control individuals were the subjects of this study. Reverse transcriptase-polymerase chain reaction analysis was performed in order to examine the messenger RNA (mRNA) expression of "lymphoid" chemokines. Furthermore, in situ hybridization studies revealed chemokine mRNA localization. Immunohistochemistry was also applied in order to identify the cell types that expressed the chemokine mRNA. STCP-1/monocyte-derived chemokine and TARC mRNA were expressed in the majority of patients with primary and secondary SS, in 2 of 4 patients with other autoimmune disorders, and in 2 of 4 controls. BCA-1, ELC, and PARC mRNA were only detected in patients with primary and secondary SS. SLC mRNA was also detected in 1 non-SS patient. The main cellular sources of chemokine mRNA were ductal epithelial cells and infiltrating mononuclear leukocytes. The expression pattern of "lymphoid" chemokine mRNA points further to the role of epithelial cells in the pathogenesis of SS and offers new insight into the potential mechanisms that could be involved in leukocyte attraction and in the in situ formation of secondary lymphoid tissue structures.

Response of embryonic chicken lymphocytes to in ovo exposure to lymphotropic viruses

Abstract Objective To examine effects of virus exposure on embryonic lymphoid organ structure, apoptosis, and lymphoid cell subpopulations. Animals Eggs of specific pathogen free (SPF) White Leghorn chickens at embryonation day (ED) 17. Procedures Eggs were inoculated with 2,000 plaque-forming units (PFU) of serotype 1 herpesvirus (Marek’s disease virus [MDV 1]), 2,000 PFU of herpesvirus of turkeys (MDV 3), or 1,000 embryo infectious doses (EID50) of infectious bursal disease virus (IBDV). On post-inoculation days (PID) 3 and 5, lymphoid organ to body weight ratios were determined, and bursa of Fabricius, thymus, and spleen were evaluated for lesions and apoptosis. Proportions of lymphoid cell subpopulations of PID-3 chicken embryos and 7- to 10-day-old chicks were quantitated by flow cytometry. Results Lymphoid organ weights were similar in virus-free, MDV 1, and IBDV groups. Embryos inoculated with 2,000 PFU MDV 3/egg had lower bursal weights than virus-free controls. In a repeated trial, MDV 3 (1,000 PFU to 4,000 PFU) did not reduce bursal weights among groups. Histologic changes were seen in bursae after MDV 1 and IBDV inoculation. Apoptosis was greater in bursae of MDV 1-infected embryos than controls. Lymphoid cell subpopulations were similar among all groups with the exception of CD8+ and IgM+ cells in spleens of IBDV-infected 10-day-old chicks. Conclusions and Clinical Relevance Infection with pathogenic strains of MDV 1 and IBDV did not alter lymphocyte subpopulations in embryos or cause complete destruction of lymphoid organs. Changes in lymphoid cell subpopulations exposed as embryos to IBDV were seen only after hatching. (Am J Vet Res 1999;60:937–941)

Histochemical characteristics of the structures of rat lymphoid organs in stress

Luminescence analysis and histochemical methods have shown that stress affects various structures of rat immunocompetent organs and decreases the contents of catecholamines, serotonin and histamine in central and peripheral immune organs. The content of biogenic amines in thymic structures increased 10, 20, and 30 days after the administration of the immunostimulator polystim against the background of stress. The results obtained indicate that polystim displays stress-protective activity and can be used in clinical practice.

Dendritic cells induce autoimmune diabetes and maintain disease via de novo formation of local lymphoid tissue.

Activation of autoreactive T cells can lead to autoimmune diseases such as insulin-dependent diabetes mellitus (IDDM). The initiation and maintenance of IDDM by dendritic cells (DC), the most potent professional antigen-presenting cells, were investigated in transgenic mice expressing the lymphocytic choriomeningitis virus glycoprotein (LCMV-GP) under the control of the rat insulin promoter (RIP-GP mice). We show that after adoptive transfer of DC constitutively expressing the immunodominant cytotoxic T lymphocyte (CTL) epitope of the LCMV-GP, RIP-GP mice developed autoimmune diabetes. Kinetic and functional studies of DC-activated CTL revealed that development of IDDM was dependent on dose and timing of antigenic stimulation. Strikingly, repeated CTL activation by DC led to severe destructive mononuclear infiltration of the pancreatic islets but also to de novo formation of islet-associated organized lymphoid structures in the pancreatic parenchyma. In addition, repetitive DC immunization induced IDDM with lymphoid neogenesis also in perforin-deficient RIP-GP mice, illustrating that CD8(+) T cell-dependent inflammatory mechanisms independent of perforin could induce IDDM. Thus, DC presenting self-antigens not only are potent inducers of autoreactive T cells, but also help to maintain a peripheral immune response locally; therefore, the induction of autoimmunity against previously ignored autoantigens represents a potential hazard, particularly in DC-based antitumor therapies.

Circumscribed lesion of the medial forebrain bundle area causes structural impairment of lymphoid organs and severe depression of immune function in rats.

Interactions between the immune system and the brain are a key element in the pathophysiology of diseases such as multiple sclerosis, neuroAIDS, and Alzheimer's, which affect large numbers of individuals and are associated with a high social cost. However, the neuroanatomical basis of brain-immune interactions has not been elucidated. We report that in Wistar rats of either sex bilateral electrolytic lesion of the medial forebrain bundle reduces body weight by 28% 7 days after lesioning, and causes widespread infections, aphagia, adypsia, structural damage to the lymphoid organs and heavy depression of T lymphocytes cytotoxicity. The following alterations occur in the immune system after those lesions: the weight of the thymus, spleen and lymphonodes is reduced by 77.9%, 49.1% and 48.4%, respectively. The thymus is atrophied and contains fewer lymphoid cells in the cortex than in the medulla. In the spleen the white pulp is reduced and lymphoid cells from periarteriolar zones and at the chords are almost absent. In lymph nodes cortical small lymphocytes are depleted and primary and secondary nodules and germinal centers all but disappear. Cytotoxicity of lymphocytes is reduced by 86.2% in the thymus, 77.6% in the spleen and 70.2% in lymph nodes. The critical area of lesion is at the medialmost portion of the medial forebrain bundle, at the preoptic area and rostral part of the anterior hypothalamus. We suggest that this area contains neural circuits that are crucial for keeping the structure of lymphoid organs and the functional integrity of the immune system.

Abrogation of the alternative complement pathway by targeted deletion of murine factor B.

To investigate the role of complement protein factor B (Bf) and alternative pathway activity in vivo, and to test the hypothesized potential genetic lethal effect of Bf deficiency, the murine Bf gene was interrupted by exchange of exon 3 through exon 7 (including the factor D cleaving site) with the neor gene. Mice heterozygous for the targeted Bf allele were interbred, yielding Bf-deficient offspring after the F1 generation at a frequency suggesting that Bf deficiency alone has no major effect on fertility or fetal development. However, in the context of one or more genes derived from the 129 mouse strain, offspring homozygous for Bf deficiency were generated at less than expected numbers (P = 0.012). Bf-deficient mice showed no gross phenotypic difference from wild-type littermates. Sera from Bf-deficient mice lacked detectable alternative complement pathway activity; purified mouse Bf overcame the deficit. Classical pathway-dependent total hemolytic activity was lower in Bf-deficient than wild-type mice, possibly reflecting loss of the alternative pathway amplification loop. Lymphoid organ structure and IgG1 antibody response to a T-dependent antigen appeared normal in Bf-deficient mice. Sensitivity to lethal endotoxic shock was not significantly altered in Bf-deficient mice. Thus, deficiency of Bf and alternative complement activation pathway led to a less dramatic phenotype than expected. Nevertheless, these mice provide an excellent model for the assessment of the role of Bf and the alternative pathway in host defense and other functions in vivo.

Ultrastructural and cytoarchitectural features of lymphoreticular organs in the colon and rectum of adult BALB/c mice

The structure and function of colonic mucosal lymphoid organs remain largely unexplored, especially in the rectum hidden within the pelvic vault. Two-month-old female BALB/c mice were anesthetized, and the entire colon was removed from cecum to anus. Distal colonic patches were then prepared for electron microscopy or were quick-frozen and sectioned for immunoperoxidase localization of B cells and T cell subsets. Aggregated lymphoid follicles were distributed irregularly along the entire colon with an average of 1.4 patches per centimeter of colon length. There were large collections of follicles opposite the ileocecal valve (cecal patches), variable numbers of patches throughout the colon, and at least one patch within 10 mm of the anus (rectal patch). Follicles were adjacent to branching crypts lined by epithelium infiltrated by lymphoid cells and containing few goblet cells. In electron micrographs, M cells were identified by their short, irregular microvilli; intraepithelial lymphoid cells; reduced lysosomal dense bodies; and an expanded tubulovesicular network. Small germinal centers were seen. Cytoarchitectural components of colonic lymphoid follicles and Peyer's patch follicles were remarkably similar, despite differences in surrounding mucosa and luminal microbial exposure. The presence of organized lymphoid tissue with M cells and germinal centers suggests that transepithelial particle transport and antigen recognition can take place in the rectum. Whether such tissue has the capacity for uptake of luminal microorganisms is of particular interest, not only because colonic follicles may be sites for local initiation of immune responses but also because they may be important entry points for systemic infection.