Formation of Peyer's patches

Cataloguing the postnatal small intestinal transcriptome during the first postnatal month

In the first postnatal month, the developing mouse intestine shifts from an immature to a mature intestine that will sustain the organism throughout the lifespan. Here, we surveyed the mouse intestine in C57Bl/6 mice by RNA-Seq to evaluate the changes in gene expression over time from the day of birth through 1 month of age in both the duodenum and ileum. We analyzed gene expression for changes in gene families that correlated with the periods of NEC susceptibility or resistance. We highlight that increased expression of DNA processing genes and vacuolar structure genes, tissue development and morphogenesis genes, and cell migration genes all correlated with NEC susceptibility, while increases in immunity gene sets, intracellular transport genes, ATP production, and intracellular metabolism genes correlated with NEC resistance. Using trends identified in the RNA-Seq analyses, we further evaluated expression of cellular markers and epithelial regulators, immune cell markers, and adenosine metabolism components. We confirmed key changes with qRT-PCR and immunofluorescence. In addition, we compared some findings to humans using human intestinal biopsies and organoids. This dataset can serve as a reference for other groups considering the role of single molecules or molecular families in early intestinal and postnatal development.

Effects of PACAP Deficiency on Immune Dysfunction and Peyer's Patch Integrity in Adult Mice

PACAP (pituitary adenylate cyclase activating polypeptide) is a widespread neuropeptide with cytoprotective and anti-inflammatory effects. It plays a role in innate and adaptive immunity, but data are limited about gut-associated lymphoid tissue. We aimed to reveal differences in Peyer's patches between wild-type (WT) and PACAP-deficient (KO) mice. Peyer's patch morphology from young (3-months-old) and aging (12-15-months-old) mice was examined, along with flow cytometry to assess immune cell populations, expression of checkpoint molecules (PD-1, PD-L1, TIM-3, Gal-9) and functional markers (CD69, granzyme B, perforin) in CD3+, CD4+, and CD8+ T cells. We found slight differences between aging, but not in young, WT, and KO mice. In WT mice, aging reduced CD8+ T cell numbers frequency and altered checkpoint molecule expression (higher TIM-3, granzyme B; lower Gal-9, CD69). CD4+ T cell frequency was higher with similar checkpoint alterations, indicating a regulatory shift. In PACAP KO mice, aging did not change cell population frequencies but led to higher TIM-3, granzyme B and lower PD-1, PD-L1, Gal-9, and CD69 expression in CD4+ and CD8+ T cells, with reduced overall T cell activity. Thus, PACAP deficiency impacts immune dysfunction by altering checkpoint molecules and T cell functionality, particularly in CD8+ T cells, suggesting complex immune responses by PACAP, highlighting its role in intestinal homeostasis and potential implications for inflammatory bowel diseases.

Formation of the junctions between lymph follicles in the Peyer's patches even before postweaning activation

Peyer's patches (PPs), which contain an abundance of B and T cells, play a key role in inducing pivotal immune responses in the intestinal tract. PPs are defined as aggregated lymph follicles, which consist of multiple lymph follicles (LFs) that may interact with each other in a synergistic manner. LFs are thought to be spherical in shape; however, the characteristics of their structure are not fully understood. To elucidate changes in the structure of PPs as individuals grow, we generated serial 2D sections from entire PPs harvested from mice at 2, 4, and 10 weeks of age and performed a 3D analysis using a software, Amira. Although the number of LFs in PPs was not changed throughout the experiment, the volume and surface area of LFs increased significantly, indicating that LFs in PPs develop continuously by recruiting immune cells, even after weaning. In response to the dramatic changes in the intestinal environment after weaning, the development of germinal centers (GCs) in LFs was observed at 4 and 10 weeks (but not 2 weeks) of age. In addition, GCs gradually began to form away from the center of LFs and close to the muscle layer where export lymphatic vessels develop. Importantly, each LF was joined to the adjacent LF; this feature was observed even in preweaning nonactivated PPs. These results suggest that PPs may have a unique organization and structure that enhance immune functions, allowing cells in LFs to have free access to adjacent LFs and egress smoothly from PPs to the periphery upon stimulation after weaning.

Molecular Drivers of Lymphocyte Organization in Vertebrate Mucosal Surfaces: Revisiting the TNF Superfamily Hypothesis

The adaptive immune system of all jawed vertebrates relies on the presence of B and T cell lymphocytes that aggregate in specific body sites to form primary and secondary lymphoid structures. Secondary lymphoid organs include organized MALT (O-MALT) such as the tonsils and Peyer patches. O-MALT became progressively organized during vertebrate evolution, and the TNF superfamily of genes has been identified as essential for the formation and maintenance of O-MALT and other secondary and tertiary lymphoid structures in mammals. Yet, the molecular drivers of O-MALT structures found in ectotherms and birds remain essentially unknown. In this study, we provide evidence that TNFSFs, such as lymphotoxins, are likely not a universal mechanism to maintain O-MALT structures in adulthood of teleost fish, sarcopterygian fish, or birds. Although a role for TNFSF2 (TNF-α) cannot be ruled out, transcriptomics suggest that maintenance of O-MALT in nonmammalian vertebrates relies on expression of diverse genes with shared biological functions in neuronal signaling. Importantly, we identify that expression of many genes with olfactory function is a unique feature of mammalian Peyer patches but not the O-MALT of birds or ectotherms. These results provide a new view of O-MALT evolution in vertebrates and indicate that different genes with shared biological functions may have driven the formation of these lymphoid structures by a process of convergent evolution.

Enteroviruses: A Gut-Wrenching Game of Entry, Detection, and Evasion

Enteroviruses are a major source of human disease, particularly in neonates and young children where infections can range from acute, self-limited febrile illness to meningitis, endocarditis, hepatitis, and acute flaccid myelitis. The enterovirus genus includes poliovirus, coxsackieviruses, echoviruses, enterovirus 71, and enterovirus D68. Enteroviruses primarily infect by the fecal-oral route and target the gastrointestinal epithelium early during their life cycles. In addition, spread via the respiratory tract is possible and some enteroviruses such as enterovirus D68 are preferentially spread via this route. Once internalized, enteroviruses are detected by intracellular proteins that recognize common viral features and trigger antiviral innate immune signaling. However, co-evolution of enteroviruses with humans has allowed them to develop strategies to evade detection or disrupt signaling. In this review, we will discuss how enteroviruses infect the gastrointestinal tract, the mechanisms by which cells detect enterovirus infections, and the strategies enteroviruses use to escape this detection.

Meconium microbiota types dominated by lactic acid or enteric bacteria are differentially associated with maternal eczema and respiratory problems in infants

BACKGROUND

Culture-dependent methods have shown that meconium, the newborn's first intestinal discharge, is not sterile, but the diversity of bacteria present in this material needs to be further characterized by means of more sensitive molecular techniques.

OBJECTIVE

Our aims were to characterize molecularly the meconium microbiota in term infants, to assess whether it contributes to the future microbiota of the infants' gastrointestinal tract, and to evaluate how it relates to lifestyle variables and atopy-related conditions.

METHODS

We applied high-throughput pyrosequencing of the 16S rRNA gene to study the meconium microbiota in twenty term newborns from a Spanish birth cohort. For comparison, we characterized the microbiota in fecal samples from seven pregnant women days before delivery and in two series of infant samples spanning the first seven months of life. We also compared our data with vaginal and skin microbiota characterized in independent studies. Different types of meconium microbiota were defined based on taxonomic composition and abundance and their associations with different factors were statistically evaluated.

RESULTS

The meconium microbiota differs from those in adult feces, vagina and skin, but resembles that of fecal samples from young infants. Meconium samples clustered into two types with different bacterial diversity, richness and composition. One of the types was less diverse, dominated by enteric bacteria and associated with a history of atopic eczema in the mother (P = 0.038), whereas the second type was dominated by lactic acid bacteria and associated with respiratory problems in the infant (P = 0.040).

CONCLUSIONS & CLINICAL RELEVANCE

Our findings suggest that the meconium microbiota has an intrauterine origin and participates in gut colonization. Although based on a small population sample, our association analyses also suggest that the type of bacteria detected in meconium is influenced by maternal factors and may have consequences for childhood health.

Expression of Neutral Glycosphingolipids in the Brain and Spleen of Mice Lacking TNF Receptor 1

We investigated the expression of neutral glycosphingolipids (GSLs) in the brain and spleen of mice lacking the gene for the tumor necrosis factor-alpha receptor p55 (TNFR1). Neutral GSLs of the ganglio-, globo-, and neolacto-series were determined in the tissues of homozygous (TNFR1-/-) and control heterozygous (TNFR1+/-) animals by high performance thin layer chromatography (HPTLC) overlay immunostaining with specific antibodies. The spleen of homozygous TNFR1 knockout mice lacked glucosylceramide substituted with palmitic acid, GlcCer(C16), and showed severe reduction in the expression of GlcCer(C24). In addition, gangliotetraosylceramide substituted with palmitic acid, Gg4Cer(C16), and globotetraosylceramide, Gb4Cer, were down-regulated in the TNFR1-/- spleen in comparison with the heterozygous control. The brain of both groups of animals (TNFR1-/- and TNFR1+/-) did not express detectable levels of Gg4Cer, Gb5Cer and Gb4Cer, but the brain of TNFR1 knockout mice expressed abundant globotriaosylceramide, Gb3Cer, compared to no expression in control heterozygous mice. nLcCer(C24) had slightly higher (1.4 fold) expression in the brain of TNFR1-/- mice compared with the control animals. This study provides in vivo evidence that TNF signaling via the TNFR1 is involved in the acquisition of a divergent GSL assembly in the brain, an immunologically privileged organ, and the spleen, typical secondary lymphoid organ.

Induction of intestinal lymphoid tissue formation by intrinsic and extrinsic signals

Since the discovery of inducer cells as a separate lineage for organogenesis of Peyer's patches in the small intestine of fetal mice, a lot of progress has been made in understanding the molecular pathways involved in the generation of lymphoid tissue and the maintenance of the lymphoid architecture. The findings that inducer cells also exist in adult mice and in humans, have a lineage relationship to natural killer cells, and can be stimulated during infections highlight their possible role in establishing innate and adaptive immune responses. Novel concepts in the development of intestinal lymphoid tissues have been made in the past few years suggesting that lymphoid organs are more plastic as previously thought and depend on antigenic stimulation. In addition, the generation of novel lymphoid organs in the gut under inflammatory conditions indicates a function in chronic diseases. The present review summarizes current knowledge on the basic framework of signals required for developing lymphoid tissue under normal and inflammatory conditions.

Oral Delivery of Pathogens from the Intestine to the Nervous System

Most therapeutic agents are delivered orally. Consequently, the major classes of therapeutically useful chemicals are partially lipophilic, small molecular weight compounds. They have reasonable permeability coefficient values across cell membranes, including those of intestinal epithelia and vascular endothelia. In contrast, large molecular weight biotechnology compounds have limited usefulness by non-injected routes as a consequence of their low membrane permeability and variable solubility. However, a wide range of infectious agents have developed strategies or have hijacked physiological routings in order to enter the host by the oral route. Efforts to address such issues have refreshed interest in mechanisms by which different types of payloads (including particulates and microorganisms) translocate across gut epithelia and then distribute to target tissues. Special attention is given to the potential role of the enteric nervous system and its plasticity.

Distinct changes in adult lymphopoiesis in Rag2-/- mice fully reconstituted by alpha4-deficient adult bone marrow cells

OBJECTIVE

alpha4 Integrins are major players in lymphoid cell trafficking and immune responses. However, their importance in lymphoid reconstitution and function, studied by antibody blockade or in genetic models of chimeric animals with alpha4(KO) embryonic stem (ES) cells, competitive repopulation experiments with fetal liver(KO) cells, or in beta1/beta7 doubly-deficient mice has yielded disparate conclusions.

MATERIALS AND METHODS

To study the role of alpha4 integrin (alpha4beta1, alpha4beta7) during adult life, we transplanted lethally irradiated Rag2(-/-) mice with alpha4(Delta/Delta) or alpha4(f/f) adult bone marrow (BM) cells and evaluated recipients at several points after transplantation.

RESULTS

Lymphomyeloid repopulation (8 months later) was entirely donor-derived in all recipients, and novel insights regarding lymphoid reconstitution and function were revealed. Thymic repopulation was impaired in all alpha4(Delta/Delta) recipients, likely because of homing defects of BM-derived progenitors, although a role of alpha4 integrin in intrathymic expansion/maturation of T cells cannot be excluded; reconstitution of gut lymphoid tissue was also greatly diminished because of homing defects of alpha4(Delta/Delta) cells; impaired immunoglobulin (Ig) M and IgE, but normal IgG responses were seen, suggesting compromised initial B-/T-cell interactions, whereas interferon-gamma production from ovalbumin-stimulated cells was increased, possibly reflecting a bias against Th2 stimulation.

CONCLUSION

These data complement previous observations by defending the role of alpha4 integrin in thymic and gut lymphoid tissue homing, and by strengthening evidence of attenuated B-cell responses in alpha4-deficient mice.

Targeting mucosal dendritic cells with microbial antigens from probiotic lactic acid bacteria

The use of vaccines against infectious microbes has been critical to the advancement of medicine. Vaccine strategies combined with, or without, adjuvants have been established to eradicate various bacterial and viral pathogens. A new generation of vaccines is being developed using specific strains of Gram-positive, lactic acid bacteria and, notably, some probiotic lactobacilli. These bacteria have been safely consumed by humans for centuries in fermented foods. Thus, they can be orally administered, are well tolerated by recipients and could be easily and economically provided to large populations. In this overview, we focus on mucosal immunity and how its cellular component(s), particularly dendritic cells, can be specifically targeted to deliver immunogenic subunits, such as the protective antigen from Bacillus anthracis (the causative agent of anthrax). An antigen-specific immune response can be elicited using specific strains of Lactobacillus acidophilus expressing the protective antigen. A mucosal, dendritic cell-targeted approach increases the bioavailability of an immunogen of interest when delivered orally by L. acidophilus. This provides an efficiently elegant natural strategy and serves a dual function as an immune-stimulating adjuvant in vivo.

Development of mucosal immune function in the intrauterine and early postnatal environment

PURPOSE OF REVIEW

There is recent evidence that immunological priming can start prenatally or in the very early life phase. This review summarizes recent progress in the field of early gut immunology with special attention to factors contributing to the intrauterine and early postnatal development of mucosal immune responses in the gut.

RECENT FINDINGS

Development and maturation of the fetal gut immune system occurs under close control of the maternal environment. Examples include maternal antibodies, cytokines, sCD14 molecules and bacterial antigens. Mouse experiments reveal that activated T cells can be detected already at birth in the fetal gut, which are supposed to be activated by signals from the maternal microbial gut flora. Human milk sCD14 is involved in the immunological priming of the developing gut immune system to Gram-negative bacteria and modulates the microbial recognition system of the gut. The development of food allergies is associated with consumption of food components like polyunsaturated fatty acids acting prenatally or in the early postnatal life span as immunomodulators.

SUMMARY

The new findings highlight the importance of very early life factors for the development of the mucosal immune functions of the gut. Therefore, the gut might be a new target to establish preventive strategies with regard to different immunologic disorders.

53BP1 deficiency in intestinal enterocytes does not alter the immediate response to ionizing radiation, but leads to increased nuclear area consistent with polyploidy

The p53-binding protein 53BP1 has been implicated in the DNA damage response and genomic instability. Previous reports have highlighted these roles in vivo in haematopoietic lineages. To investigate the importance of 53BP1 to the DNA damage response in epithelial cells in vivo, we have investigated the role of 53BP1 in mediating apoptosis and proliferation within the murine small intestine following gamma-irradiation. 53BP1 deficiency does not affect the immediate response to gamma-irradiation with normal levels of apoptosis, proliferation and p53 and p21 accumulation. However, 48 h post-gamma-irradiation there was a significant accumulation of cells with much larger nuclei marked by p53 and p21 accumulation. These data reflect increases in polyploidy observed 53BP1-/- deficient fibroblasts following gamma-irradiation. At 72 h post-irradiation both the 4N and 8N populations were significantly increased in 53BP1-/- MEFS. Taken together, these results show that following in vivo exposure to gamma-irradiation, 53BP1 is dispensable for signalling apoptosis and cell-cycle arrest in the intestinal epithelium. However, it is important for prevention of genomic instability within this epithelial cell population.

Pyloric tonsil as a novel gut-associated lymphoepithelial organ of the chicken

The pyloric tonsil is a novel peripheral lymphoepithelial organ of the gastrointestinal tract in the chicken. It forms a complete lymphoid ring at the beginning of the duodenum, where crypts of Lieberkühn are transformed to tonsillar crypts with lymphoepithelial lining. The oesophageal (described previously) and pyloric tonsils are characteristic of the chicken, while they are absent in mammals. The lymphoid system develops from the middle germ layer, the mesoderm, and forms connections with the ecto- and endoderm, namely the skin and gut, respectively. These connections are based on the lymphoepithelial lining of the crypts, and provide gates for environmental antigens. Recent findings, taken together with the literature, suggest that in birds the lymphoid system forms connections with the endoderm-derived organs that are anatomically and histologically more extensive than the ectoderm-derived ones, which may be explained by the absence of regional lymph nodes, and the less developed lymphoid circulation of the skin.

Molecular Networks Orchestrating GALT Development

During evolution, the development of secondary lymphoid organs has evolved as a strategy to promote adaptive immune responses at sites of antigen sequestration. Mesenteric lymph nodes (LNs) and Peyer's patches (PPs) are localized in proximity to mucosal surfaces, and their development is coordinated by a series of temporally and spatially regulated molecular events involving the collaboration between hematopoietic, mesenchymal, and, for PPs, epithelial cells. Transcriptional control of cellular differentiation, production of cytokines as well as adhesion molecules are mandatory for organogenesis, recruitment of mature leukocytes, and lymphoid tissue organization. Similar to fetal and neonatal organogenesis, lymphoid tissue neoformation can occur in adult individuals at sites of chronic stimulation via cytokines and TNF-family member molecules. These molecules represent new therapeutic targets to manipulate the microenvironment during autoimmune diseases.

Peyer's patches are required for the induction of rapid Th1 responses in the gut and mesenteric lymph nodes during an enteric infection

The Peyer's patches (PP) and mesenteric lymph nodes (MLN) are structural components of the gut-associated lymphoid tissues and contribute to the induction of immune responses toward infection in the gastrointestinal tract. These secondary lymphoid organs provide structural organization for efficient cellular interactions and the initiation of primary adaptive immune responses against infection. Immunity against primary infection with the enteric apicomplexan parasite, Eimeria vermiformis, depends on the rapid induction of local Th1 responses. Lymphotoxin (LT)-deficient mice which have various defects in secondary lymphoid organs were infected with E. vermiformis. The relative susceptibility of LTalpha(-/-), LTbeta(-/-), LTalpha(+/-)beta(+/-) mice and bone marrow chimeras, indicated that rapid protective Th1 responses required both PP and MLN. Moreover, the timing of Th1 induction in both MLN and gut was dependent on the presence of PP suggesting a level of cooperation between immune responses induced in these distinct lymphoid structures. The delay in Th1 induction was attributable to the delayed arrival of a broad range of dendritic cell subsets in the MLN and a substantial reduction of CD8alpha(-)CD11b(high) B220(-) dendritic cells in PP-deficient mice.

Blocking the alpha 4 integrin-paxillin interaction selectively impairs mononuclear leukocyte recruitment to an inflammatory site

Antagonists to alpha4 integrin show promise for several autoimmune and inflammatory diseases but may exhibit mechanism-based toxicities. We tested the capacity of blockade of alpha4 integrin signaling to perturb functions involved in inflammation, while limiting potential adverse effects. We generated and characterized mice bearing a Y991A mutation in alpha4 integrin [alpha4(Y991A) mice], which blocks paxillin binding and inhibits alpha4 integrin signals that support leukocyte migration. In contrast to the embryonic-lethal phenotype of alpha4 integrin-null mice, mice bearing the alpha4(Y991A) mutation were viable and fertile; however, they exhibited defective recruitment of mononuclear leukocytes into thioglycollate-induced peritonitis. Alpha4 integrins are essential for definitive hematopoiesis; however, the alpha4(Y991A) mice had intact lymphohematopoiesis and, with the exception of reduced Peyer's patches, normal architecture and cellularity of secondary lymphoid tissues. We conclude that interference with alpha4 integrin signaling can selectively impair mononuclear leukocyte recruitment to sites of inflammation while sparing vital functions of alpha4 integrins in development and hematopoiesis.

Developmentally regulated intestinal expression of IFN-gamma and its target genes and the age-specific response to enteric Salmonella infection

Young infants are highly susceptible to systemic dissemination of enteric pathogens such as Salmonella typhimurium when compared with older individuals. The mechanisms underlying this differential susceptibility have not been defined clearly. To better understand this phenomenon, we examined the responses of adult mice and preweaned pups to oral infection by S. typhimurium. We found clear age-specific differences, namely, an attenuated intestinal inflammatory response and a higher systemic bacterial burden in the pups compared with the adults. To elucidate the molecular basis for these differences, we obtained a microarray-based profile of gene expression in the small intestines of uninfected adult and preweaned animals. The results indicated a striking age-dependent increase in the intestinal expression of a number of IFN-gamma-regulated genes involved in antimicrobial defense. This finding was confirmed by real-time quantitative PCR, which also demonstrated an age-dependent increase in intestinal expression of IFN-gamma. The developmental up-regulation of the IFN-gamma-regulated genes was dependent on both IFN-gamma and a normal commensal microflora, as indicated by experiments in IFN-gamma-knockout mice and germfree mice, respectively. However, the increase in expression of IFN-gamma itself was independent of the commensal flora. The functional importance of IFN-gamma in the immunological maturation of the intestine was confirmed by the observation that the response of adult IFN-gamma-knockout animals to S. typhimurium infection resembled that of the wild-type pups. Our findings thus reveal a novel role for IFN-gamma in the developmental regulation of antimicrobial responses in the intestine.

Fate and function of lymphoid tissue inducer cells

The discovery that Peyer's patch and lymph node development is regulated by the collaboration between fetal hematopoietic cells and mesenchymal cells has thrown new light on our understanding of the mechanisms underlying the formation of lymphoid organs. Lymphoid tissue inducer cells trigger a coordinated series of events leading to cell clustering and changes in gene expression and differentiation. Nevertheless, many questions regarding the origin, recruitment and fate of the inducer cells and cellular crosstalk with neighboring cells remain unanswered.

Isolated lymphoid follicles can function as sites for induction of mucosal immune responses

Isolated lymphoid follicles (ILFs) are organized lymphoid structures in the small intestine. ILFs were recently identified in the murine small intestine; however, the function of ILFs is unknown. To better understand ILFs and the role they play in the intestinal immune response, we have examined the composition of ILFs, the factors that are involved in the genesis of ILFs, and the ability of ILFs to support antigen-specific immunoglobulin production. We found that ILFs contain predominantly B-2 B lymphocytes, and CD4(+) TCRbeta(+) T lymphocytes. Similar to the formation of Peyer's patches (PPs), lymphotoxin beta receptor (LTbetaR)-dependent events are required for ILF formation; however, the timing of these events and the cellular source of LT differ. ILF formation can occur de novo in response to luminal stimuli and requires LT-sufficient B lymphocytes and TNF receptor I function for full maturation. The epithelium over ILFs resembles the PP follicle-associated epithelium, as M cells are present and pathogens such as Yersinia can be bound and taken up into the underlying follicle. Total fecal IgA production is not augmented in animals possessing ILFs; however, the production of antigen-specific IgA is increased in animals possessing ILFs orally challenged with Salmonella typhimurium. Similar to PPs, ILFs can support antigen-specific IgA production following oral immunization. These findings support the concept that ILFs are formed in response to mucosal challenges, and may play a physiological role in the production of antigen-specific intestinal IgA.

How the Gut Links Innate and Adaptive Immunity

Mucosal surfaces represent the main sites in which environmental microorganisms and antigens interact with the host. Sentinel cells, including epithelial cells, lumenal macrophages, and intraepithelial dendritic cells, continuously sense the environment and coordinate defenses for the protection of mucosal tissues. The mucosal epithelial cells are crucial actors in coordinating defenses. They sense the outside world and respond to environmental signals by releasing chemokines and cytokines that recruit inflammatory and immune cells to control potential infectious agents and to attract cells able to trigger immune responses. Among immune cells, dendritic cells (DC) play a key role in controlling adaptive immune responses, due to their capacity to internalize foreign materials and to present antigens to naive T and B lymphocytes, locally or in draining organized lymphoid tissues. Immune cells recruited in epithelial tissues can, in turn, act upon the epithelial cells and change their phenotype in a process referred to as epithelial metaplasia.

Lymphotoxin beta receptor signaling induces the chemokine CCL20 in intestinal epithelium

BACKGROUND & AIMS

The follicle-associated epithelium (FAE) that overlies Peyer's patches (PPs) exhibits distinct features compared with the adjacent villus epithelium. Besides the presence of antigen-sampling membranous M cells and the down-regulation of digestive functions, it constitutively expresses the chemokine CCL20. The mechanisms that induce FAE differentiation and CCL20 expression are poorly understood. The aim of this work was to test whether lymphotoxin beta receptor signaling (LTbetaR), which plays a central role in PPs' organogenesis, mediates CCL20 gene expression in intestinal epithelial cells.

METHODS

CCL20, lymphotoxin beta (LTbeta) and LTbetaR expression were monitored during embryonic development by in situ hybridization of mouse intestine. The human intestinal epithelial cell line T84 was used to study CCL20 expression following LTalpha(1)/beta(2) stimulation. In vivo CCL20 expression following agonistic anti-LTbetaR antibody treatment was studied by laser microdissection and quantitative RT-PCR.

RESULTS

CCL20 was expressed in the FAE before birth at the time when the first hematopoietic CD4(+)CD3(-) appeared in the PP anlage. LTbetaR was expressed in the epithelium during PP organogenesis, making it a putative target for LTalpha(1)beta(2)signals. In vitro, CCL20 was induced in T84 cells upon LTbetaR signaling, either using an agonistic ligand or anti-LTbeta receptor agonistic antibody. LTalpha(1)beta(2)-induced CCL20 expression was found to be NF-kappaB dependent. LTbetaR signaling up-regulated CCL20 expression in the small intestinal epithelium in vivo.

CONCLUSIONS

Our results show that LTbetaR signaling induces CCL20 expression in intestinal epithelial cells, suggesting that this pathway triggers constitutive production of CCL20 in the FAE.

Expression of glycosphingolipids in lymph nodes of mice lacking TNF receptor 1: biochemical and flow cytometry analysis

The expression of gangliosides and neutral glycosphingolipids (GSLs) in the lymph nodes of mice lacking the gene for the tumour necrosis factor-alpha receptor p55 (TNFR1) has been investigated. GSL expression in the tissues of mice homozygous (TNFR1-/-) or heterozygous (TNFR1+/-) for the gene deletion was analysed by flow cytometry and high-performance thin-layer chromatography (HPTLC) followed by immunostaining with specific antibodies. HPTLC immunostaining revealed that lymph nodes from TNFR1-/- mice had reduced expression of ganglioside GM1b and GalNAc-GM1b, neolacto-series gangliosides, as well as the globo- (Gb3, Gb4 and Gb5) and ganglio-series (Gg3 and Gg4) neutral GSLs. Flow cytometry of freshly isolated lymph node cells showed no significant differences in GSL expression, except for the GalNAc-GM1b ganglioside, which was less abundant on T lymphocytes from TNFR1-/- lymph nodes. In TNFR1-/- mice, GalNAc-GM1b+/CD4+ T cells were twofold less abundant (3.8% vs 7.6% in the control mice), whereas GalNAc-GM1b+/CD8+ T cells were fourfold less abundant (5.0% vs 20.2% in the control mice). This study provides in vivo evidence that TNF signalling via the TNFR1 is important for the activation of GM1b-type ganglioside biosynthetic pathway in CD8 T lymphocytes, suggesting its possible role in the effector T lymphocyte function.

Organogenesis of peripheral lymphoid organs

The discovery that lymphotoxin alpha (LTalpha) knockout mice lack peripheral lymphoid tissues reformed the study of organogenesis of peripheral lymphoid tissues from a research field that was solely descriptive and dependent on histological methods to one requiring all modern technologies. The concepts of inducer cells for organogenesis of peripheral lymphoid tissues as a separate hematopoietic lineage and of mesenchymal organizer cells have been established through this progress. These discoveries led to the comprehension of the basic framework of the events during organogenesis of peripheral lymphoid tissues. However, many important questions remain unanswered. This review discusses those questions which have arisen from our studies on the organogenesis of Peyer's patches.

Lymphotoxin/light, lymphoid microenvironments and autoimmune disease

Much of the efficiency of the immune system is attributed to the high degree of spatial and temporal organization in the secondary lymphoid organs. Signalling through the lymphotoxin (LT) pathway is a crucial element in the maintenance of this organized microenvironment. The effect of altering lymphoid microenvironments on immune responses remains relatively unexplored. Inhibitors of the LT and LIGHT pathways have been shown to reduce disease in a wide range of autoimmune models. This approach has provided a tool to probe the effect of manipulation of the microenvironment on both normal and pathological immune responses.

Molecular insights into congenital disorders of the digestive system

Recent work is providing new insights into molecular mechanisms of digestive system development and their alteration in clinically significant disorders. An understanding of these mechanisms has largely been gained through the use of animal models, because many of the basic processes required in embryogenesis are functionally conserved among species. Such conserved factors include cell-cell signaling pathways and the regulation of gene expression. Disruption of these pathways have been implicated in several congenital disorders of the digestive system, including Hirschsprung disease, malrotation, altered sphincter development, Meckel diverticulum, biliary atresia, Alagille syndrome, pancreatic heterotopias, and pancreatic agenesis. In this review, we highlight recent studies in digestive system development, which elucidate mechanisms underlying congenital disorders of the human digestive system.

CD4+CD3- cells induce Peyer's patch development: role of alpha4beta1 integrin activation by CXCR5

CD4+CD3- cells are the predominant hematopoietic cells found in mouse fetal intestine. We prove their role as Peyer's patch (PP)-inducing cells by transfer into neonatal PP-deficient mice. To test the requirement of chemokines and adhesion molecules in induction of PP, we studied mice deficient in CXCR5 and/or alpha4beta1 integrin-mediated adhesion. CXCR5-/- mice have CD4+CD3- cells, which are inefficient in inducing PP formation. We show here that CXCR5/CXCL13 signaling activates alpha4beta1 integrin on CD4+CD3- cells. Blocking of beta1 integrin or VCAM-1, the ligand of alpha4beta1 integrin, inhibits PP formation. This study demonstrates the link between chemokine receptors and adhesion molecules that regulates stromal/hematopoietic cell interaction leading to PP formation.