Myeloid-lymphoid ontogeny in the rhesus monkey (Macaca mulatta)

Establishment of a functional immune system has important implications for health and disease, yet questions remain regarding the mechanism, location, and timing of development of myeloid and lymphoid cell compartments. The goal of this study was to characterize the ontogeny of the myeloid-lymphoid system in rhesus monkeys to enhance current knowledge of the developmental sequence of B-cell (CD20, CD79), T-cell (CD3, CD4, CD8, FoxP3), dendritic cell (CD205), and macrophage (CD68) lineages in the fetus and infant. Immunohistochemical assessments addressed the temporal and spatial expression of select phenotypic markers in the developing liver, thymus, spleen, lymph nodes, gut-associated lymphoid tissue (GALT), and bone marrow with antibodies known to cross-react with rhesus cells. CD3 was the earliest lymphoid marker identified in the first trimester thymus and, to a lesser extent, in the spleen. T-cell markers were also expressed midgestation on cells of the liver, spleen, thymus, and in Peyer's patches of the small and large intestine, and where CCR5 expression was noted. A myeloid marker, CD68, was found on hepatic cells near blood islands in the late first trimester. B-cell markers were observed mid-second trimester in the liver, spleen, thymus, lymph nodes, bone marrow spaces, and occasionally in GALT. By the late third trimester and postnatally, secondary follicles with germinal centers were present in the thymus, spleen, and lymph nodes. These results suggest that immune ontogeny in monkeys is similar in temporal and anatomical sequence when compared to humans, providing important insights for translational studies.

Aberrant pulmonary lymphatic development in the nitrofen mouse model of congenital diaphragmatic hernia

PURPOSE

Many infants develop a postsurgical chylothorax after diaphragmatic hernia repair. The pathogenesis remains elusive but may be owing to dysfunctional lymphatic development. This study characterizes pulmonary lymphatic development in the nitrofen mouse model of CDH.

METHODS

CD1 pregnant mice were fed nitrofen/bisdiamine (N/B) or olive oil at E8.5. At E14.5 and E15.5, lung buds were categorized by phenotype: normal, N/B without CDH (N/B - CDH), or N/B with CDH (N/B+CDH). Anti-CD31 was used to localize all endothelial cells, while anti-LYVE-1 was used to identify lymphatic endothelial cells in lung buds using immunofluorescence. Differential protein expression of lymphatic-specific markers was analyzed.

RESULTS

Lymphatic endothelial cells localized to the mesenchyme surrounding the airway epithelium at E15.5. CD31 and LYVE-1 colocalization identified lymphatic endothelial cells. LYVE-1 expression was upregulated in N/B+CDH lung buds in comparison to N/B - CDH and normal lung buds by immunofluorescence. Western blotting shows that VEGF-D, LYVE-1, Prox-1, and VEGFR-3 expression was upregulated in N/B+CDH lung buds in comparison to N/B - CDH or control lung buds at E14.5.

CONCLUSIONS

Lung lymphatics are hyperplastic in N/B+CDH. Upregulation of lymphatic-specific genes suggests that lymphatic hyperplasia plays an important role in dysfunctional lung lymphatic development in the nitrofen mouse model of CDH.

The ontogeny of New Zealand groper (Polyprion oxygeneios) lymphoid organs and IgM

This study investigates the ontogeny of New Zealand groper (Polyprion oxygeneios) immune system, a new species for aquaculture in the Southern Pacific Ocean. In the eggs, both lysozyme and IgM were detected. Egg IgM was found at 1.07-1.56 μg/g wet weight and consisted of monomers compared to the polymerized IgM found in adult serum. In larvae, the head-kidney (HK) was first observed at 6 dph, followed by the spleen at 16 dph, and thymus at 20 dph, and within these organs IgM(+) cells were first detected in the HK (12 dph), then the spleen (32 dph) and finally in the thymus and the gastrointestinal tract (45 dph). Low levels of Igμ heavy chain transcripts were detected at 2 and 3 dph and they increased at 9 dph. Igμ expression further increased from day 45 onwards. In juveniles (115 dph), the HK and blood showed similar percentages of IgM(+) cells as the adult groper. These results highlight the important maturation steps that occur during the development of the immune system in the marine teleost P. oxygeneios.

Conservation of CD1 protein expression patterns in the chicken

The CD1 molecules are cell-surface proteins that bind and present foreign lipids and glycolipids to T cells in a manner similar to the MHC system. While the mammalian CD1 antigen presentation pathway is well characterized, little is known about CD1 in non-mammalian vertebrates. Previous studies have identified two CD1 homologues in the chicken. We developed a monoclonal antibody designated NL1-1.A1 specific for the chCD1-1 isoform and have used this to characterize CD1 expression in tissues and cells of normal adult and embryonic chickens. The chCD1-1 isoform is expressed on a high proportion of cells in the spleen and bursa. Cells in the spleen that stain for CD1 are also positive for IgM and consistent with identification of these as B cells. In the skin, chCD1-1 is expressed on cells with dendritic morphology along the dermal-epidermal boundary and in epidermal sheets consistent with chicken Langerhans cells. Staining of cells in the medullary region of the chicken thymus was also observed. The CD1 proteins in mammals traffic to intracellular compartments to acquire lipid antigens for subsequent presentation to T cells on the surface. Consistent with data from mammal CD1 proteins, chCD1-1 partially co-localized with a lysosomal marker in the myeloid cell line BM2. Taken together, these data support broad distribution of chCD1-1 in both lymphoid and non-lymphoid tissues of the chicken that is remarkably similar to the distribution of CD1 isoforms in mammals.

Jugular lymphatic sacs in first-trimester fetuses with normal nuchal translucency

OBJECTIVE

To assess the ultrasonographic appearance of the jugular lymphatic sacs (JLS) in first-trimester fetuses with a normal nuchal translucency (NT).

METHODS

Seventy-five fetuses with a normal NT thickness (< 95(th) percentile) were examined weekly between 11 and 17 weeks of gestation. After measurement of the NT thickness, the neck region was examined using both transvaginal and transabdominal ultrasonography for the presence of JLS. If present, their dimensions were measured in three directions and the volume was calculated using the formula for a spheroid. Data were analyzed using multilevel analysis.

RESULTS

Seventy-five fetuses were evaluated and a total of 243 ultrasound examinations of the neck region were performed. In 25 (33%) of the 75 fetuses, the JLS could be observed once or more than once. In 19 fetuses JLS were visualized once, in five fetuses twice and in one fetus three times. In total, the JLS were visualized 32 times (n = 15 bilaterally, n = 15 only the left JLS and n = 2 only the right JLS). Relatively greater NT thickness was associated with a higher probability of the presence of JLS, although this was not statistically significant (NT < 1 mm, probability 0.07; NT 1-2 mm, probability 0.15, P = 0.10; NT > 2 mm, probability 0.20, P = 0.08). Gestational age was predictive for the presence of JLS, with the highest probability between 13 and 15 weeks of gestation (P < 0.01). No relationship was found between gestational age and the volumes of the left and right JLS.

CONCLUSION

The JLS can be visualized on ultrasound examination in a significant proportion of fetuses with normal NT, most often between 13 and 15 weeks of gestation, and this does not seem to be associated with any abnormality in these fetuses.

Human fetal lymphoid tissue-inducer cells are interleukin 17-producing precursors to RORC+ CD127+ natural killer-like cells

The human body contains over 500 individual lymph nodes, yet the biology of their formation is poorly understood. Here we identify human lymphoid tissue-inducer cells (LTi cells) as lineage-negative RORC+ CD127+ cells with the functional ability to interact with mesenchymal cells through lymphotoxin and tumor necrosis factor. Human LTi cells were committed natural killer (NK) cell precursors that produced interleukin 17 (IL-17) and IL-22. In vitro, LTi cells gave rise to RORC+ CD127+ NK cells that retained the ability to produce IL-17 and IL-22. Postnatally, similar populations of LTi cell-like cells and RORC+ CD127+ NK cells were present in tonsils, and both secreted IL-17 and IL-22 but no interferon-gamma. Our data indicate that lymph node organogenesis is controlled by an NK cell precursor population with adaptive immune features and demonstrate a previously unappreciated link between the innate and adaptive immune systems.

Organizer-like reticular stromal cell layer common to adult secondary lymphoid organs

Mesenchymal stromal cells are crucial components of secondary lymphoid organs (SLOs). Organogenesis of SLOs involves specialized stromal cells, designated lymphoid tissue organizer (LTo) in the embryonic anlagen; in the adult, several distinct stromal lineages construct elaborate tissue architecture and regulate lymphocyte compartmentalization. The relationship between the LTo and adult stromal cells, however, remains unclear, as does the precise number of stromal cell types that constitute mature SLOs are unclear. From mouse lymph nodes, we established a VCAM-1(+)ICAM-1(+)MAdCAM-1(+) reticular cell line that can produce CXCL13 upon LTbetaR stimulation and support primary B cell adhesion and migration in vitro. A similar stromal population sharing many characteristics with the LTo, designated marginal reticular cells (MRCs), was found in the outer follicular region immediately underneath the subcapsular sinus of lymph nodes. Moreover, MRCs were commonly observed at particular sites in various SLOs even in Rag2(-/-) mice, but were not found in ectopic lymphoid tissues, suggesting that MRCs are a developmentally determined element. These findings lead to a comprehensive view of the stromal composition and architecture of SLOs.

Roles of embryonic and adult lymphoid tissue inducer cells in primary and secondary lymphoid tissues

The nomenclature "embryonic lymphoid tissue inducer (LTi) cell" reflects the fundamental role of the cell in secondary lymphoid tissue organization. In addition, it is equally important in primary lymphoid tissue development as it regulates central tolerance to self-antigens in the thymus. An adult LTi cell constitutively expresses two sets of tumor necrosis factor (TNF) family members, whereas its embryonic counterpart expresses only one. The first set is lymphotoxin (LT)alpha, LTbeta, and TNalpha, which are essential for the secondary lymphoid organogenesis during embryogenesis and for maintaining an organized secondary lymphoid structure during adulthood. The second set is OX40- and CD30-ligands, which are critical for memory T cell generation. Adult LTi cells regulate adaptive immune responses by providing LTbetaR signals to stromal cells to maintain secondary lymphoid tissue structure, and determine adaptive immune responses by providing OX40 and CD30 survival signals to activated T cells in memory T cell generation. Along with the consideration of the roles of embryonic LTi cells in primary and secondary lymphoid tissues, this review highlights the roles of adult LTi cells in secondary lymphoid tissue function.

From induced to programmed lymphoid tissues: the long road to preempt pathogens

In mammalian fetuses, ontogeny dictates the development of secondary lymphoid tissues, the spleen, the lymph nodes and the Peyer's patches. In adults, commensals, infectious microbes and inflammation induce the formation of small reversible lymphoid tissues resembling lymph nodes or Peyer's patches. Crucial to lymphoid-tissue genesis is lymphotoxin-beta receptor-mediated activation of inflammatory effectors and structural chemokines. This pathway might have existed since the advent of the vertebrate lymphocyte system to organize local adaptive immunity in response to microbes; however, it only operates in the absence of microbes in mammals, resulting in the development of secondary lymphoid tissues and in preempting pathogens.

The transcriptional coactivator Maml1 is required for Notch2-mediated marginal zone B-cell development

Signaling mediated by various Notch receptors and their ligands regulates diverse biological processes, including lymphoid cell fate decisions. Notch1 is required during T-cell development, while Notch2 and the Notch ligand Delta-like1 control marginal zone B (MZB) cell development. We previously determined that Mastermind-like (MAML) transcriptional coactivators are required for Notchinduced transcription by forming ternary nuclear complexes with Notch and the transcription factor CSL. The 3 MAML family members (MAML1-MAML3) are collectively essential for Notch activity in vivo, but whether individual MAMLs contribute to the specificity of Notch functions is unknown. Here, we addressed this question by studying lymphopoiesis in the absence of the Maml1 gene. Since Maml1(-/-) mice suffered perinatal lethality, hematopoietic chimeras were generated with Maml1(-/-), Maml1(+/-), or wild-type fetal liver progenitors. Maml1 deficiency minimally affected T-cell development, but was required for the development of MZB cells, similar to the phenotype of Notch2 deficiency. Moreover, the number of MZB cells correlated with Maml1 gene dosage. Since all 3 Maml genes were expressed in MZB cells and their precursors, these results suggest that Maml1 is specifically required for Notch2 signaling in MZB cells.

CD248/Endosialin is dynamically expressed on a subset of stromal cells during lymphoid tissue development, splenic remodeling and repair

Studies of stromal cell populations in lymphoid tissue (LT) have been hampered by a lack of selective markers. Here, we show that CD248 (Endosialin/TEM1) is a stromal marker that is differentially expressed on fibroblasts and pericytes in the thymus, lymph node and spleen. Expression is high during LT development but largely disappears in the adult. CD248 is re-expressed in a Salmonella-induced model of splenic enlargement; peak expression corresponding to the peak of splenic enlargement. These results suggest that CD248 expression helps define a subset of LT stromal cells which play a role in remodelling during tissue development, infection and repair.

Cutting edge: Uniqueness of lymphoid chemokine requirement for the initiation and maturation of nasopharynx-associated lymphoid tissue organogenesis

CD3(-)CD4(+)CD45(+) inducer cells are required for the initiation of mucosa-associated organogenesis of both nasopharynx-associated lymphoid tissues (NALT) and Peyer's patches (PP) in the aerodigestive tract. CXCL13(-/-) mice and mice carrying the paucity of lymph node T cell (plt) mutation and lacking expression of CCL19 and CCL21 accumulate CD3(-)CD4(+)CD45(+) cells at the site of NALT but not of PP genesis. Although NALT was observed to develop in adult CXCL13(-/-) and plt/plt mice, the formation of germinal centers in CXCL13(-/-) mice was affected, and their population of B cells was much lower than in the NALT of CXCL13(+/-) mice. Similarly, fewer T cells were observed in the NALT of plt/plt mice than in control mice. These findings indicate that the initiation of NALT organogenesis is independent of CXCL13, CCL19, and CCL21. However, the expression of these lymphoid chemokines is essential for the maturation of NALT microarchitecture.

Regulation of T cell responses in the developing human fetus

Although human T cells enter the peripheral lymphoid tissues early during fetal development, the adaptive immune system in the fetus has largely been regarded as functionally immature and unresponsive to stimulation. In this study, we show that depletion of fetal CD4+CD25(high) T regulatory (T(Reg)) cells, which are present at high frequency in fetal lymphoid tissues, results in vigorous T cell proliferation and cytokine production in vitro, even in the absence of exogenous stimulation. Analysis of CD4+ and CD8(+) T cell populations revealed a large subset of cells that expressed the early activation Ag, CD69. We show that this population represents a subset of highly reactive fetal T cells actively suppressed by fetal CD4+CD25(high) T(Reg) cells during development. These findings indicate that fetal T cells are, in the absence of CD4+CD25(high) T(Reg) cells, highly responsive to stimulation and provide evidence for an important role for CD4+CD25(high) T(Reg) cells in controlling T cell responses in utero.

[Immunomorphological lymphocytic-tissue associations in the anterior gastrointestinal tract in human fetus]

Prevalence of T-cell system of the immunity is found in the pharyngeal, lingual and palatine tonsils and lymph nodes. B-lymphocytes are much less numerous. Adenocytes consolidation in the structure of "pharyngeal hypophysis" is considered as additional part of the anterior hypophysis. The structure of the mucous membrane in the region of pharyngeal hypophysis is described. This membrane is deprived of protective epithelium and mucous glands.

The pre-immune variable kappa repertoire of swine is selectively generated from certain subfamilies of Vkappa2 and one Jkappa gene

Combinatorial diversity is highly restricted during formation of the pre-immune heavy chain repertoire of swine, raising the question of whether the same is true for the pre-immune light chain repertoire. Before addressing this question, we first used competitive PCR to show that kappa and lambda light chains in swine are equally expressed in mature B cells similar to the situation in humans but alike that in other studied Ungulates. This justified efforts to examine the repertoire of both light chain types. These studies also revealed that lambda is preferentially expressed at sites of B cells lymphogenesis, perhaps because of the use of a surrogate light chain containing lambda5. Data are presented here on >100 VkappaJkappa-containing transcripts and approximately 180 genomic Vkappa genes to show that >90% of the pre-immune repertoire is generated from three subfamilies of IGKV2 genes and one of five Jkappa segments. The kappa locus contains >or=50 IGKV2 genes belonging to at least five subfamilies and an undetermined but perhaps equal number of IGKV1 genes. The porcine IGKV1 and IGKV2 genes share 87% sequence similarity with their human counterparts and Jkappa1 through Jkappa5 share sequence and organizational homology with those in sheep, horse, human and mouse. Swine have a single Ckappa gene. These findings contrast with those from rodents and primates but are reminiscent of those on the pre-immune heavy chain repertoire of swine in that it is generated using a relatively restricted number of gene segments. These restricted pre-immune repertoires may reflect the minimal exposure of the fetus to maternal factors and environmental antigens. The significance for swine immunology of characterizing the pre-immune repertoire is discussed.

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.

Systematic microanatomical analysis of CXCL13 and CCL21 in situ production and progressive lymphoid organization in rheumatoid synovitis

CXCL13 and CCL21 have been functionally implicated in lymphoid tissue organization both in the upstream phases of lymphoid tissue embryogenesis and in ectopic lymphoid neogenesis in transgenic mice. Here, we analyzed the relationship between CXCL13 and CCL21 production and lymphoid tissue organization in rheumatoid synovitis as a model of a naturally occurring ectopic lymphoneogenesis. Through systematic analysis of mRNA and protein expression, we defined the microanatomical relationship between CXCL13 and CCL21 in progressive aggregational and structural phases of synovial inflammatory infiltrate. We provide the first direct in situ evidence that production of CXCL13 and CCL21 (rather than simply protein binding) is associated with inflammatory lymphoid tissue formation and development with the demonstration, in organized aggregates, of a secondary lymphoid organ-like compartmentalization and vascular association. Notably, the presence of CXCL13 and CCL21 (protein and mRNA) was also demonstrated in non-organized clusters and minor aggregational stages, providing evidence that their induction can take place independently and possibly upstream of T-B compartmentalization, CD21(+) follicular dendritic cell network differentiation and germinal center formation. Our data support the concept that, under inflammatory conditions, CXCL13 and CCL21 participate in lymphoid tissue microanatomical organization, attempting to recapitulate, in an aberrant lymphoid neogenetic process, their homeostatic and morphogenetic physiologic functions.

Frequency and potential cause of bronchus-associated lymphoid tissue in fetal lungs

Bronchus-associated lymphoid tissue consists of lymphoid follicles with or without a germinal center within the bronchial wall. Bronchus-associated lymphoid tissue is part of the integrated mucosal immune system and present in about 50% of healthy infants. We examined a series of 141 fetal and neonatal lungs and detected bronchus-associated lymphoid tissue in 100% of cases with amniotic infection while postpartum perinatal pneumonia did not elicit bronchus-associated lymphoid tissue formation. Only rarely and in low density, bronchus-associated lymphoid tissue was present in non-infected fetuses. The in utero formation of bronchus-associated lymphoid tissue seems to be a reactive phenomenon and - as has been shown in another study - does not portend an adverse prognosis.

Inducible lymphoid tissues in the adult gut: recapitulation of a fetal developmental pathway?

The intestinal immune system faces an extraordinary challenge from the large numbers of commensal bacteria and potential pathogens that are restrained by only a single layer of epithelial cells. Here, I discuss evidence that the intestinal immune system develops an extensive network of inducible, reversible lymphoid tissues that contributes to the vital equilibrium between the gut and the bacterial flora. I propose that this network is induced by cryptopatches, which are small clusters of dendritic cells and lymphoid cells that are identical to fetal inducers of lymph-node and Peyer's-patch development.

Abnormal lymphatic development in trisomy 16 mouse embryos precedes nuchal edema

Ultrasound measurement of increased nuchal translucency is a method of risk assessment for heart malformations and trisomy 21 in human pregnancy. The developmental background of this nuchal edema is still not sufficiently understood. We have studied the process in trisomy 16 mice that show nuchal edema and heart malformations. We used trisomy 16 and wild-type (WT) embryos from embryonic day (E) 12.5 to E18.5. In WT embryos at E13, bilateral jugular lymphatic sacs are visible that share a lymphatic-venous membrane with the jugular vein. We could not in any case discern a valve between these vessels. At E14 in the TS16 embryos, the lymphatic sacs become enlarged showing abnormally thickened endothelium, specifically at the site of the membrane. In these embryos, severe edema develops in the nuchal region. There is a very close colocalisation of the nerves with the vascular structures. The start of reorganization of the jugular lymphatic sac to a lymph node is observed in both wild-type and TS16 but is diminished in the latter. In conclusion, abnormal size and structure of the jugular lymphatic sacs coincides with the development of nuchal edema. A disturbance of lymphangiogenesis might be the basis for increased nuchal translucency that is often observed in diseased human fetuses.

Lymphoid Organogenesis in the Intestine

Lymphoid organogenesis is dependent upon a series of intricate cellular interactions involving adhesion molecules, chemokines, and cytokines that generate fully compartmentalized lymphoid structures. Development of organized lymphoid structures in the intestine begins prenatally and continues through adulthood, with constant adaptations to changes in the luminal flora. While much is known about the mechanisms that govern the development of macroscopic intestinal lymphoid structures (mesenteric lymph node and Peyer's patches), the organogenesis of the microscopic lymphoid tissues (including cryptopatches and isolated lymphoid follicles) is an emerging field. This review examines the current state of knowledge about organogenesis of the known types of organized lymphoid tissue in the intestine and identifies unique and common features in the development of each of the structures discussed.

Cellular composition of pancreas-associated lymphoid tissue during human fetal pancreatic development

AIM

To study human fetal pancreatic tissue between 15 weeks of gestation and term, analysing the development of pancreatic lymphoid tissue and focusing on the presence and maturational status of dendritic cells (DCs). During normal human fetal pancreatic development lymphoid tissue arises in and around the pancreas. DCs are antigen-presenting cells which are capable of initiating immunity, but are also essential in inducing and maintaining T-cell tolerance.

METHODS AND RESULTS

First, the presence and general composition of intra- and peripancreatic lymphoid tissue was investigated by histology and immunohistochemistry with antibodies to CD3, CD4, CD8, CD14, CD20, CD68, and CD79. Intrapancreatic lymphoid tissue (IPLT) appeared to be present only from 29 weeks of gestation onwards, and had a similar composition to peripancreatic lymphoid tissue (PPLT), which was found in all 23 specimens examined. Both forms of lymphoid tissue had an architecture similar to lymph nodes, with separate B- and T-lymphocyte areas and scattered macrophages. DCs were investigated in detail by immunohistochemistry for CD1a, CD83, CD86, CD123, Langerin, and DC-LAMP. Both Langerin, a marker for immature DCs, as well as DC-LAMP, a marker for mature DCs, were expressed by cells in both the IPLT and PPLT at all ages examined.

CONCLUSION

The presence of DCs at all developmental stages, expressing various maturation-related markers, in addition to the general composition of the human fetal PPLT and IPLT suggests that this is fully functional and has a function comparable to peripheral lymph nodes.

Thymic origin of intestinal alphabeta T cells revealed by fate mapping of RORgammat+ cells

Intestinal intraepithelial T lymphocytes (IELs) are likely to play a key role in host mucosal immunity and, unlike other T cells, have been proposed to differentiate from local precursors rather than from thymocytes. We show here that IELs expressing the alphabeta T cell receptor are derived from precursors that express RORgammat, an orphan nuclear hormone receptor detected only in immature CD4+CD8+ thymocytes, fetal lymphoid tissue-inducer (LTi) cells, and LTi-like cells in cryptopatches within the adult intestinal lamina propria. Using cell fate mapping, we found that all intestinal alphabeta T cells are progeny of CD4+CD8+ thymocytes, indicating that the adult intestine is not a significant site for alphabeta T cell development. Our results suggest that intestinal RORgammat+ cells are local organizers of mucosal lymphoid tissue.

An essential function for the nuclear receptor RORgamma(t) in the generation of fetal lymphoid tissue inducer cells

Lymphoid tissue inducer (LTi) cells are associated with early development of lymph nodes and Peyer's patches. We show here that during fetal life the nuclear hormone receptor RORgamma(t) is expressed exclusively in and is required for the generation of LTi cells. RORgamma(t+) LTi cells provide essential factors, among which lymphotoxin-alpha1beta2 is necessary but not sufficient for activation of the mesenchyma in lymph node and Peyer's patch anlagen. This early LTi cell-mediated activation of lymph node and Peyer's patch mesenchyma forms the necessary platform for the subsequent development of mature lymphoid tissues.

Possible involvement of glial cell line-derived neurotrophic factor and its receptor, GFRalpha1, in survival and maturation of thymocytes

The glial cell line-derived neurotrophic factor (GDNF) and its receptors (GFR) play important roles in the promotion of survival and differentiation of central and peripheral neuronal populations. We show that GFRalpha1, a component of GDNF receptor, was expressed in thymocytes at an early stage of thymocyte-development and was involved in the survival of thymocyte precursors. GFRalpha1and GDNF were expressed in thymus, but not in spleen or lymph nodes in adult mice. During embryonic thymocyte development, GFRalpha1 was predominantly expressed on thymocytes from days 14.5 to 16.5 of gestation, and thereafter its expression gradually declined. In adult thymus, GFRalpha1 was expressed only on CD4(-)CD8(-) double-negative (DN) thymocytes, but not on CD4(+)CD8(+) double-positive or single-positive thymocytes. It was strongly expressed on RAG2(-/-) thymocytes arrested at the DN stage, and ist expression was reduced during their differentiation after in vivo anti-CD3 antibody stimulation. Additionally, fetal thymocyte precursors grew in serum-free medium of the fetal thymus organ culture system in the presence of recombinant GDNF (rGDNF), while the cells without rGDNF died. These results suggested that GDNF/GFRalpha1 are involved in the survival of both the nervous system and DN immature thymocytes.

Ectopic LT alpha beta directs lymphoid organ neogenesis with concomitant expression of peripheral node addressin and a HEV-restricted sulfotransferase

Lymph node (LN) function depends on T and B cell compartmentalization, antigen presenting cells, and high endothelial venules (HEVs) expressing mucosal addressin cell adhesion molecule (MAdCAM-1) and peripheral node addressin (PNAd), ligands for naive cell entrance into LNs. Luminal PNAd expression requires a HEV-restricted sulfotransferase (HEC-6ST). To investigate LT alpha beta's activities in lymphoid organogenesis, mice simultaneously expressing LT alpha and LT beta under rat insulin promoter II (RIP) control were compared with RIPLT alpha mice in a model of lymphoid neogenesis and with LT beta-/- mice. RIPLT alpha beta pancreata exhibited massive intra-islet mononuclear infiltrates that differed from the more sparse peri-islet cell accumulations in RIPLT alpha pancreata: separation into T and B cell areas was more distinct with prominent FDC networks, expression of lymphoid chemokines (CCL21, CCL19, and CXCL13) was more intense, and L-selectin+ cells were more frequent. In contrast to the predominant abluminal PNAd pattern of HEV in LT beta-/- MLN and RIPLT alpha pancreatic infiltrates, PNAd was expressed at the luminal and abluminal aspects of HEV in wild-type LN and in RIPLT alpha beta pancreata, coincident with HEC-6ST. These data highlight distinct roles of LT alpha and LT alpha beta in lymphoid organogenesis supporting the notion that HEC-6ST-dependent luminal PNAd is under regulation by LT alpha beta.

Lymphocyte traffic in lymphoid organ neogenesis: differential roles of Ltalpha and LTalphabeta

In these studies the differential roles of LTalpha and LTalphabeta complex have been discussed with regard to development of lymphoid organs in ontogeny and in inflammation, LTalpha is necessary for PLNand MLN, most likely as both LTalpha and LTalphabeta complex, whereas only LTalphabeta is required for MLN. Both are involved in the cellularity of the NALT. When expressed as a transgene, LTa alone can induce cellular accumulation and MAdCAM, but not PNAd, an epitope associated with PLN HEV. These data suggest that LTalphabeta complex plays a crucial role in PNAd. One hypothesis is that LTalphabeta induces PNAd through modification via an HEV sulfotransferase. RIPLTalpha.RIPLTbeta mice will provide an important tool to investigate this question.

Lymphotoxin beta receptor induces sequential activation of distinct NF-kappa B factors via separate signaling pathways

Lymphotoxin beta receptor (LTbetaR)-induced activation of NF-kappaB in mouse embryo fibroblasts was mediated by the classical pathway and by an alternative or second pathway. The classical pathway involved the IkappaB kinase (IKK)beta- and IKKgamma-dependent degradation of IkappaBalpha and resulted in the rapid but transient activation of primarily RelA-containing NF-kappaB dimers. The alternative or second pathway proceeded via NF-kappaB-inducing kinase (NIK)-, IKKalpha-, and protein synthesis-dependent processing of the inhibitory NF-kappaB2 p100 precursor protein to the p52 form and resulted in a delayed but sustained activation of primarily RelB-containing NF-kappaB dimers. This second pathway was independent of the classical IKK complex, which is governed by its central IKKgamma regulatory subunit. The sequential engagement of two distinct pathways, coupled with the negative feedback inhibition of RelA complexes by NF-kappaB-induced resynthesis of IkappaBalpha, resulted in a pronounced temporal change in the nature of the NF-kappaB activity during the course of stimulation. Initially dominant RelA complexes were replaced with time by RelB complexes. Therefore, the alternative activation path mediated by processing of p100 was necessary for sustained NF-kappaB activity in mouse embryo fibroblasts in response to LTbetaR stimulation. Based on the phenotype of mice deficient in various components of the LTbetaR-induced activation of p100 processing, we conclude that this pathway is critically involved in the function of stromal cells during the generation of secondary lymphoid organ microarchitectures.

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.

Morphological study of development and functional activity of palatine tonsils in embryonic age

Palatine tonsils play an important role in the development of the immune system, being the first organ in the lymph system which analyses and reacts to antigenic stimulation. In this study, the peritonsillar area of Waldeyer's ring was investigated in 88 normal human embryos which were examined histologically and immunohistochemically. The progressive development of palatine tonsils during embryonic life is discussed. The first appearance of tonsils is in about the 14th-15th week followed by a parallel development of B- and T-cell regions which accounts for the high incidence of non mucosa-associated lymphoid tissue lymphomas among all tonsillar lymphomas and the higher incidence of T-cell-lymphomas, in comparison to the mucosa-associated lymphoid tissue of the digestive system. The way in which the human body develops the palatine tonsils quickly and prepares them to react to the first antigenic stimulation, are discussed.

Mammalian twisted gastrulation is essential for skeleto-lymphogenesis

Dorsoventral patterning depends on the local concentrations of the morphogens. Twisted gastrulation (TSG) regulates the extracellular availability of a mesoderm inducer, bone morphogenetic protein 4 (BMP-4). However, TSG function in vivo is still unclear. We isolated a TSG cDNA as a secreted molecule from the mouse aorta-gonad-mesonephros region. Here we show that TSG-deficient mice were born healthy, but more than half of the neonatal pups showed severe growth retardation shortly after birth and displayed dwarfism with delayed endochondral ossification and lymphopenia, followed by death within a month. TSG-deficient thymus was atrophic, and phosphorylation of SMAD1 was augmented in the thymocytes, suggesting enhanced BMP-4 signaling in the thymus. Since BMP-4 promotes skeletogenesis and inhibits thymus development, our findings suggest that TSG acts as both a BMP-4 agonist in skeletogenesis and a BMP-4 antagonist in T-cell development. Although lymphopenia in TSG-deficient mice would partly be ascribed to systemic effects of runtiness and wasting, our findings may also provide a clue for understanding the pathogenesis of human dwarfism with combined immunodeficiency.

Mesenchymal expression of Foxl1, a winged helix transcriptional factor, regulates generation and maintenance of gut-associated lymphoid organs

The Foxl1 gene, which encodes a winged helix transcriptional regulator, is expressed in the mesenchymal layer of developing and mature gastrointestinal tract. Foxl1-deficient mice exhibit various defects not only in the epithelial layer of the gastrointestinal tract but also in gut-associated lymphoid tissues. In the small intestine of Foxl1-deficient mice, the formation of Peyer's patches is affected, particularly in the caudal region. This alteration is shown to be due to the delayed formation of Peyer's patches organizing centers as revealed by the expressions of VCAM1 and IL-7 receptor alpha-chain at 17.5 days postcoitus. Peyer's patch defects are concordant with the significantly decreased expression of Lymphotoxin beta-receptor in the caudal region of fetal intestine. Foxl1 is suggested to regulate the responsiveness of fetal intestinal mesenchymal cells to inductive signals mediated by Lymphotoxins during Peyer's patch organogenesis. In addition, constitutive outgrowth of colonic patches due to defects in radioresistant stromal components of colonic patches are seen in Foxl1-deficient mice. Because of the functional similarities of hypertrophic colonic patches to those seen in hapten-induced experimental colitis, this hypertrophy is suggested to involve Lymphotoxin beta-receptor signaling. Together, the data suggest that Foxl1 might be involved in cellular responses of gut-associated lymphoid tissues dependent upon the Lymphotoxins/Lymphotoxin beta-receptor axis.

The lymphoid and immunohaematopoietic tissues of the embryonic brushtail possum ( Trichosurus vulpecula)

The lymphoid and immunohaematopoietic tissues of the embryonic and full-term brushtail possums was investigated histologically and immunohistochemically using antibodies to the T- and B-cell markers, CD3, CD5, CD79a and CD79b. No clearly defined thymus, bone marrow, spleen, lymph nodes, gut-associated lymphoid tissues or bronchus-associated lymphoid tissues were observed histologically. The liver was haematopoietic and contained erythrocytic and granulocytic precursors. No mature lymphocytes were observed histologically or detected using antibodies to T- and B-cell markers in any of the tissues. These results are consistent with other studies of the early postnatal tissues of other marsupials and support the proposition that neonatal marsupials are substantially reliant on maternal immunological protection at the time of birth and for a significant period of pouch life.

Histological and immunohistochemical study of the lymphoid tissue in the normal stomach of the gnotobiotic pig

Animal models have been developed in which the role of Helicobacter pylori in the pathogenesis of different gastroduodenal diseases can be investigated. The gnotobiotic pig was one of the first animal models used. In this model, Helicobacter pylori infection causes gastritis, which shows some similarities to that in humans, such as the development of mucosa-associated lymphoid tissue (MALT). Hence, this animal model can be used to study the development of MALT in the normal stomach. The aim of our study is to see if lymphoid tissue is present or absent in the normal stomach of gnotobiotic pigs before birth and if so, to investigate its development and composition as a function of gestational age and location in the stomach. Therefore, we studied 82 foetal piglets using routine histology and immunohistochemistry. Our findings show that lymphoid tissue is present at birth. It is composed of lymphoid nodules, a diffuse mononuclear infiltrate and intra-epithelial lymphocytes. The development is a sequential process. The lymphoid tissue in the stomach at birth is composed of the immunohistochemically different immunocompetent cells normally present. In conclusion, MALT is present in normal foetal gnotobiotic pig gastric mucosa, and in this model the stomach is no exception to the rest of the gastrointestinal tract.

Nucleolar organizer regions: their significance in the maturation of the gut-associated lymphoid tissue

Nucleolar organizer regions (NORs) are important for regulating protein synthesis. Our study points towards the possibility of determining gut-associated lymphoid (GAL) cell proliferation and maturation in fetuses from ten to 35 weeks of gestation by means of the Argyrophilic (Ag) staining for NORs. This technique was performed on paraffin-embedded small intestine and mesentery tissue sections from 30 fetuses at the 10th, 14th, 15th, 19th, 20th, 23rd, 31st, and 35th week of gestation. Our results showed that there was no statistically significant difference concerning the mean AgNOR values, between GAL cells and mesentery lymphoid cells (2.81 +/- 0.63 to 2.63 +/- 0.71; p > 0.1), from ten to 15 weeks' gestation. In this specific period, the lymphoid cells first appear and Peyer's patches are formed in the small intestinal mucosa. In contrast, in fetuses from 19 to 35 fetal weeks NOR counts were statistically significantly greater in GAL cells than in fetuses from ten to 15 gestational weeks (as compared to NOR counts in GAL cells in fetuses at an earlier fetal age) (3.28 +/- 0.73 to 2.81 +/- 0.63). Mean AgNOR values in mesentery lymphoid cells remained unchanged (2.62 +/- 0.57) (p < 0.001). In conclusion, increasing protein synthesis from the 19th till the 35th week of gestation is indicative of immune system maturation, given that at the same time GAL cells become fully mature. Mesentery lymphoid cells pass (migrate) to the small intestinal mucosa from the bloodstream, and they form the whole out-associted lymphoid tissue (GALT) organ (Peyer's patches). The lymphatics associated with mucosa associated lymphoid tissue (MALT) are all efferent; it seems that during fetal life due to genetically determined factors, draining vessels operating as afferent lymphatics at that time, change to efferent (where the immunological response is greatly amplified) as embryonal life progresses.

Ontogeny and genetics of the hemato/lymphopoietic system

During embryogenesis there is a sequential, temporal appearance of increasingly more-complex hematopoietic cells beginning with unipotential progenitors, proceeding to multipotential (myeloid, erythroid and lymphoid) progenitors and culminating with adult-repopulating hematopoietic stem cells. Current research has established an important role for the aorta-gonads-mesonephros region of the mouse embryo in the generation of multipotential progenitors and hematopoietic stem cells. Comparisons of normal and hematopoietic-cell-mutant mouse embryos have revealed several genes pivotal in hematopoietic stem cell generation/function. Other genes have been implicated in the critical generation of lymphoid lineage potential. Thus, an understanding of the cellular and molecular interactions within the midgestation aorta-gonads-mesonephros region offers insight into the mechanisms of hematopoietic lineage specification during ontogeny and perhaps will lead to a more complete knowledge of the adult hematopoietic system.

Ex vivo development of functional human lymph node and bronchus-associated lymphoid tissue

We introduce a novel in vivo model of human mucosal immunity, based on the implantation of human fetal bronchial mucosa and autologous peribronchial lymph node (PLN) in the severe combined immunodeficiency (SCID) mouse. In the SCID host, human fetal bronchi implanted alone retain macrophages and mast cells but lose T cells. In contrast, fetal bronchi co-implanted with PLN contain, in addition to macrophages and mast cells, numerous T cells and B cells, often clustered in intramucosal bronchus-associated lymphoid tissue (BALT). Functionally, bronchus-PLN cografts are able to mount robust alphabeta and gammadelta T-cell-mediated immune responses to Pseudomonas aeruginosa and 3,4-epoxy-3-methyl-1-butyl-diphosphate challenges. No other autologous lymphoid organ (bone marrow, thymus, liver) allows for BALT development in co-implanted bronchi, which suggests special ontogenetic and functional relations between extramucosal PLN and intramucosal BALT. Overall, the bronchus-PLN cograft appears as a promising model for human bronchial immune development and function. Our study is the first to document long-term ex vivo maintenance of functional human lymph nodes as native appendices to mucosal tissue. Our results, therefore, suggest a simple strategy for developing similar experimental models of human immune function in other mucosae.

[The order of lymphatic organs involvement in developing immune system of human fetus and its significance in perinatal pathology]

The liver, thymus, spleen, lymph nodes, palatine and pharyngeal tonsils, appendix and Peyer's patch were studied by morphological and immune methods in more than 100 human embryos of 3 to 34 weeks of development. The order of some organs development in the immune system is established. Key periods in the development of the thymus (5-12 weeks) and 18 weeks when peripheral organs enter the immune system are specified. Inherited perinatal pathology in abnormal lymphocytic composition in the organ is illustrated by the appendix.

Non-cell autonomous requirement for thebloodlessgene in primitive hematopoiesis of zebrafish

Vertebrate hematopoiesis occurs in two distinct phases, primitive (embryonic) and definitive (adult). Genes that are required specifically for the definitive program, or for both phases of hematopoiesis, have been described. However, a specific regulator of primitive hematopoiesis has yet to be reported. The zebrafish bloodless (bls) mutation causes absence of embryonic erythrocytes in a dominant but incompletely penetrant manner. Primitive macrophages appear to develop normally in bls mutants. Although the thymic epithelium forms normally in bls mutants, lymphoid precursors are absent. Nonetheless, the bloodless mutants can progress through embryogenesis, where red cells begin to accumulate after 5 days post-fertilization (dpf). Lymphocytes also begin to populate the thymic organs by 7.5 dpf. Expression analysis of hematopoietic genes suggests that formation of primitive hematopoietic precursors is deficient in bls mutants and those few blood precursors that are specified fail to differentiate and undergo apoptosis. Overexpression of scl, but not bmp4 or gata1, can lead to partial rescue of embryonic blood cells in bls. Cell transplantation experiments show that cells derived from bls mutant donors can differentiate into blood cells in a wild-type host, but wild-type donor cells fail to form blood in the mutant host. These observations demonstrate that the bls gene product is uniquely required in a non-cell autonomous manner for primitive hematopoiesis, potentially acting via regulation of scl.

Requirement for the NF-kappaB family member RelA in the development of secondary lymphoid organs

The transcription factor nuclear factor (NF)-kappaB has been suggested to be a key mediator of the development of lymph nodes and Peyer's patches. However, targeted deletion of NF-kappaB/ Rel family members has not yet corroborated such a function. Here we report that when mice lacking the RelA subunit of NF-kappaB are brought to term by breeding onto a tumor necrosis factor receptor (TNFR)1-deficient background, the mice that are born lack lymph nodes, Peyer's patches, and an organized splenic microarchitecture, and have a profound defect in T cell-dependent antigen responses. Analyses of TNFR1/RelA-deficient embryonic tissues and of radiation chimeras suggest that the dependence on RelA is manifest not in hematopoietic cells but rather in radioresistant stromal cells needed for the development of secondary lymphoid organs.

Expression of Golli mRNA during development in primary immune lymphoid organs of the rat

The gene-of-the-oligodendrocyte lineage (Golli)-MBP transcription unit contains three Golli-specific exons together with eight exons of the "classical" myelin basic protein (MBP) gene, yielding alternatively spliced proteins which share amino acid sequence with MBP. Unlike MBP, a late antigen expressed only in the nervous system, Golli gene products are expressed pre- and post-natally at many sites. In this study, we determined the sequence of Golli in rat by RT-PCR and 5' RACE and showed that Golli sequences are expressed in primary lymphoid organs as early as e16.5, which could explain the anergic rat T cell response we previously observed in Golli-induced meningitis.

Cellular distribution of napsin (kidney-derived aspartic protease-like protein, KAP) mRNA in the kidney, lung and lymphatic organs of adult and developing mice

Kidney-derived aspartic protease-like protein (KAP), initially identified in the mouse kidney, is a novel aspartic protease exclusively expressed in the lung and spleen as well as the kidney. Its orthologues have been identified in the human and rat, and termed napsin. We performed in situ hybridization analysis to determine the cellular expression of napsin mRNA in the kidney, lung, and lymphatic organs of adult mice and to demonstrate, for the first time, its expression patterns in ontogeny. In the adult mouse kidney, extremely intense signals for napsin mRNA were observed in the proximal straight and convoluted tubules, in agreement with a previous study. The first signals for napsin mRNA during nephrogenesis occurred selectively in mesonephric tubules at embryonic day 13, and in metanephric tubules from embryonic day 14. In the lung, a distribution restricted to type II alveolar cells or their precursors was found from embryonic day 15, at the onset of type II cell differentiation, to the adult stage. In the spleen, the mRNA was expressed in lymph nodules of the white pulp and the marginal zone-namely, B-lymphocyte-rich regions from postnatal day 0 to adult. The lymph node and Peyer's patch displayed similar expression patterns, but T cell-dependent areas in these organs and the thymus lacked such signals. These findings suggest that mouse napsin possesses crucial functional roles not only in the kidney but also in the lung and lymphatic tissues, even during fetal stages.

The earliest stages of B cell development require a chemokine stromal cell-derived factor/pre-B cell growth-stimulating factor

Environmental factors essential for the first stages of B lymphopoiesis remain elusive. Here, we report that immediately after commitment to B lineage, precursors become dependent on a chemokine SDF-1 and its receptor CXCR4 using mutant and radiation chimeric mice. In bone marrow, generation of the earliest identifiable B cell precursor populations requires CXCR4. In fetal liver, we identified Lin(-)CD19(-)c-kit(+)IL-7Ralpha(+)AA4.1(+), the earliest unipotent B cell precursor population, and found that its development was severely affected in SDF-1(-/-) embryos but not in IL-7(-/-) embryos. Lin(-) T cell progenitors appeared normal in SDF-1(-/-) embryos. Moreover, SDF-1 exhibited specific biologic activities on the earliest B cell precursors. SDF-1 provides the first example of a cytokine responsible for the earliest B lineage stages.

Prenatal and adult growth hormone gene expression in rat lymphoid organs

Growth hormone (GH) exerts its immune effects on mature lymphocytes through an autocrine/paracrine mechanism. We investigated the prenatal synthesis of GH mRNA in rat lymphoid organs using the sensitive in situ RT-PCR methodology. We show that GH transcripts are detectable in the thymus and liver of the 18-day fetus. At this stage, all thymocytes are immature and express the GH gene. In fetal liver, GH gene expression was localized in circulating lymphocytes and in hematopoietic cells surrounding GH mRNA-negative hepatocytes. In situ GH gene expression in fetal lymphoid organs was confirmed by in vitro RT-PCR showing that the amplified product from fetal lymphoid tissues was similar to the product obtained from the pituitary. Moreover, GH gene expression was detected in the thymus, spleen, and ileum Peyer's patches of adult rat, with a localization restricted to the lymphocytes and endothelial and smooth muscle cells of blood vessels. The autocrine/paracrine expression of the GH gene by lymphoid and hematopoietic cells during fetal growth might influence the generation of regulatory cells involved in immunity and hematopoiesis.