Quantitative Analysis of NKX2-3 Expression in Human Colon: An Immunohistochemical Study

In mice, Nkx2-3 homeodomain transcription factor defines the vascular specification of secondary and tertiary lymphoid tissues of the intestines. In human studies, polymorphisms in NKX2-3 have been identified as a susceptibility factor in inflammatory bowel diseases, whereas in mice, its absence is associated with protection against experimental colitis and enhanced intestinal epithelial proliferation. Here, we investigated the expression of NKX2-3 in normal, polyp, and adenocarcinoma human colon samples using immunohistochemistry and quantitative morphometry, correlating its expression with endothelial and mesenchymal stromal markers. Our results revealed that the expression of NKX2-3 is regionally confined to the lamina propria and lamina muscularis mucosae, and its production is restricted mostly to endothelial cells and smooth muscle cells with variable co-expression of CD34, alpha smooth muscle antigen (αSMA), and vascular adhesion protein-1 (VAP-1). The frequency of NKX2-3-positive cells and intensity of expression correlated inversely with aging. Furthermore, in most colorectal carcinoma samples, we observed a significant reduction of NKX2-3 expression. These findings indicate that the NKX2-3 transcription factor is produced by both endothelial and non-endothelial tissue constituents in the colon, and its expression changes during aging and in colorectal malignancies. (J Histochem Cytochem XX: XXX-XXX, XXXX).

Absence of Nkx2-3 induces ectopic lymphatic endothelial differentiation associated with impaired extramedullary stress hematopoiesis in the spleen

The red and white pulps as two main parts of the spleen are arranged around distinct types of vasculature, and perform significantly different functions in both humans and mice. Previous observations indicated a profound alteration of the local vessel specialization in mice lacking Nkx2-3 homeodomain transcription factor, including contradictory results suggesting presence of an ectopic lymphatic vascular structure. Furthermore, how the absence of Nkx2-3 and the consequential changes in endothelial components affect the extramedullary hematopoietic activity restricted to the splenic red pulp is unknown. In this work, we investigated the role of Nkx2-3 homeodomain transcription factor as a major morphogenic determinant for vascular specification, and its effect in the extramedullary hematopoiesis following acute blood loss and pharmacological stimulation of megakaryocyte differentiation after treatment with thrombopoietin-receptor mimetic Romiplostim. We found that, in mice lacking Nkx2-3, Prox1-positive lymphatic capillaries containing gp38/CD31 double positive lymphatic endothelial cells develop, arranged into an extensive meshwork, while the Clever1-positive venous segments of red pulp blood vasculature are absent. This lymphatic endothelial shift is coupled with a severely compromised splenic erythropoiesis and a significantly reduced splenic megakaryocyte colony formation following Romiplostim treatment in mice lacking Nkx2-3. These findings indicate that the shift of microvascular patterning in the absence of Nkx2-3 includes the emergence of ectopic Prox1-positive lymphatic vessels, and that this pivoting towards lymph node-like vascular patterning is associated with an impaired reserve hematopoietic capacity of the splenic red pulp.

Global alteration of colonic microRNAome landscape associated with inflammatory bowel disease

Inflammatory Bowel Disease (IBD) is characterized by chronic inflammation of the gastrointestinal tract that associates with, among others, increased risk of colorectal cancer. There is a growing evidence that miRNAs have important roles in pathological processes, such as inflammation or carcinogenesis. Understanding the molecular mechanisms such as alterations in microRNAome upon chronic intestinal inflammation is critical for understanding the exact pathomechanism of IBD. Hence, we conducted a genome wide microRNAome analysis by applying miRNA-Seq in a rat model of experimental colitis, validated the data by QPCR, examined the expression of a selection of precursor and mature miRNAs, performed in depth biological interpretation using Ingenuity Pathway Analysis and tested the obtained results on samples derived from human patients. We identified specific, interdependent expression pattern of activator/repressor transcription factors, miRNAs and their direct targets in the inflamed colon samples. Particularly, decreased expression of the miR-200 family members (miR-200a/b/c,-141, and -429) and miR-27b correlates with the reduced level of their enhancers (HNF1B, E2F1), elevated expression of their repressors (ZEB2, NFKB1) and increased expression of their target genes (ZEB2, RUNX1). Moreover, the marked upregulation of six miR-27b target genes (IFI16, GCA, CYP1B1, RUNX1, MEF2C and MMP13) in the inflamed colon tissues is a possible direct consequence of the lack of repression due to the downregulated miRNA-27b expression. Our data indicate that changes in microRNAome are associated with the pathophysiology of IBD, consequently, microRNAs offer potential targets for the diagnosis, prognosis and treatment of IBD.

Role of adipose-associated lymphoid tissues in the immunological homeostasis of the serosal surface

Although not typical lymphoid organs, analysis of the visceral adipose-associated lymphoid tissues has recently substantially expanded our knowledge about the immunological features of these elusive compartments. Recent data have highlighted their considerable complexity in cellular organization and interactions in several biological processes, including adaptive immune responses, tissue plasticity to accommodate mesenchymal stem cells and progenitors, and providing a suitable microenvironment for serosal tumor propagation. This review aims to present a comprehensive view of the adipose-associated lymphoid tissues in local and systemic immune responsiveness, with particular emphasis on the omental and mesenteric lymphoid tissues in the serosal defense of abdominal organs.

Single-center study of autoimmune encephalitis-related autoantibody testing in Hungary

OBJECTIVE

Autoantibody detection is crucial for the early diagnosis of autoimmune encephalitis (AIE) since prompt therapy can determine the disease outcome. Here, we report a single-center 6-year retrospective study of autoantibody testing in AIE in the Hungarian population.

METHODS

Serum and/or cerebrospinal fluid (CSF) autoantibody tests were performed using cell-based indirect immunofluorescence assay for AIE diagnosis. Samples were provided by neurology clinics as part of a nationwide program. Test results were analyzed for samples received during the period from 2012 to 2018.

RESULTS

We tested 1,247 samples from 1,034 patients with suspected AIE. Autoantibodies were present in 60 patients (5.8% of total). The distribution of patients with different autoantibodies by age and sex was as follows: NMDAR (70%), mostly in young females, LGI1 (15%) in middle-aged males, GABA_B R (12%) in elderly males, and Caspr2 (7%) in males. Long-term follow-up was conducted in 30 patients with repeated test requests, of which 17 remained positive, and 13 switched to negative.

CONCLUSION

We report the most comprehensive clinical laboratory study of autoantibody testing in AIE in the Hungarian population. Our results show that the frequency of different autoantibody types in AIE corresponds to the data described in the literature.

Foliate Lymphoid Aggregates as Novel Forms of Serous Lymphocyte Entry Sites of Peritoneal B Cells and High-Grade B Cell Lymphomas

The cellular homeostasis of lymphoid tissues is determined by the continuous interactions of mobile hematopoietic cells within specialized microenvironments created by sessile stromal cells. In contrast to the lymph nodes and mucosal lymphoid tissues with well-defined entry and exit routes, the movement of leukocytes in the peritoneal cavity is largely unknown. In this study, we report that, in addition to the omental milky spots and fat-associated lymphoid clusters, in mice, the serous surface of the mesenteric adipose streaks contains lymphocyte-rich organoids comprised of a highly compacted leaf-like part connected to the adipose tissue that can also efficiently bind B cells and high-grade B cell lymphoma (diffuse large B cell lymphoma) cells. Denoted as foliate lymphoid aggregates (FLAgs), these structures show incomplete T/B segregation and a partially differentiated stromal architecture. LYVE-1-positive macrophages covering FLAgs efficiently bind i.p. injected normal B cells as well as different types of diffuse large B cell lymphoma cells. Within FLAgs, the lymphocytes compartmentalize according to their chemokine receptor pattern and subsequently migrate toward the mesenteric lymph nodes via the mesenteric lymphatic capillaries. The blood supply of FLAgs includes short vascular segments displaying peripheral lymph node addressin, and the extravasation of lymphocytes to the omental and mesenteric adipose tissues is partly mediated by L-selectin. The appearance of i.p. injected cells in mesenteric lymph nodes suggests that the mesentery-associated lymphatics may also collect leukocytes from the fat-associated lymphoid clusters and FLAgs, thus combining the mucosal and serous exit of mobile leukocytes and increasing the range of drainage sites for the peritoneal expansion of lymphoid malignancies.

[Paraneoplastic neurologic syndromes: laboratory diagnostics and immunological aspects]

Paraneoplastic neurologic syndromes (PNS) and autoimmune encephalitis (AE) are rare neurological disorders, which have similar symptoms, but vary in outcome and treatment strategy. In our retrospective statistical study we evaluated the autoantibody test results of serum and CSF from 2362 patients with suspected PNS and 1034 patients with suspected AE. For autoantibody testing, immunoblot assay (PNS) and cell-based indirect immunofluorescence assay (AE) were used. Autoantibodies were present in 8% of patients with suspected PNS: anti-Yo > anti-Hu > anti-Ma2 > anti-CV2 > anti-titin > anti-Zic4 > anti-amphiphysin > anti-Ri > anti-GAD65 > anti-Sox1 > anti-recoverin. Mostly elderly women were affected. Autoantibodies were present in 5.8% of patients with suspected AE: anti-NMDAR (young women) > anti-LGI1 (middle-aged men) > anti-GABABR (elderly men) > anti-Caspr2 (adult men). Our results correspond to the data described in the literature. The number of patients with suspected PNS and AE shows an increasing tendency, where the autoantibody testing with modern laboratory diagnostic methods helps in the early introduction of the appropriate therapy.

Differential Effects of the Absence of Nkx2-3 and MAdCAM-1 on the Distribution of Intestinal Type 3 Innate Lymphoid Cells and Postnatal SILT Formation in Mice

Seeding of leukocytes to developing lymphoid tissues in embryonic and early postnatal age and to the mucosa throughout adulthood depends on the interaction between endothelial MAdCAM-1 addressin and its cognate ligand α4β7 integrin. Nkx2-3 as a transcriptional regulator of MAdCAM-1 controls vascular patterning in visceral lymphoid tissues in mice, and has been identified as a susceptibility factor for inflammatory bowel diseases in humans, associated with lymphoid neogenesis in the inflamed intestines. The role of Nkx2-3 in the organogenesis of the solitary intestinal lymphoid tissues (SILTs) involving type 3 innate lymphoid cells (ILC3) is still unknown. Here we investigated the effect of Nkx2-3 on the postnatal distribution of intestinal ILC3s and the development of SILTs, comparing these to mice lacking MAdCAM-1, but preserving Nkx2-3. At 1 week of age small intestines (SI) contained significantly higher number of ILC3s relative to the colon, with a substantial reduction in MAdCAM-1^−/− mice compared to C57BL/6 controls. One week later SI ILC3 number decreased in all genotypes, the number of colonic ILC3 of both Nkx2-3-deficient and Nkx2-3-heterozygous mice significantly increased. On the fourth postnatal week a further reduction of SI ILC3s was observed in both Nkx2-3-deficient and Nkx2-3-heterozygous mice, while in the colon the number of ILC3s showed a significant reduction in all genotypes. At 1 week of age only sporadic SILT components were present in all genotypes. By the second week mice deficient for either Nkx2-3 or MAdCAM-1 showed absence of SILT maturation compared to their relevant controls, lacking mature isolated lymphoid follicles (ILF). By the fourth week both Nkx2-3-deficient and Nkx2-3-heterozygous mice showed a similar distribution of ILFs relative to cryptopatches (CP), whereas in MAdCAM-1^−/− mice CPs and immature ILFs were present, mature ILFs were scarce. Our data demonstrate that the complete absence of MAdCAM-1 partially impairs intestinal seeding of ILC3s and causes partial blockade of SILT maturation, without affecting peripheral lymph node development. In contrast, the inactivation of Nkx2-3 permits postnatal seeding, and its blocking effect on SILT maturation prevails at later stage, thus other adhesion molecules may compensate for the intestinal homing of ILC3s in the absence of MAdCAM-1.

IL-22-Independent Protection from Colitis in the Absence of Nkx2.3 Transcription Factor in Mice

The transcription factor Nkx2.3 regulates the vascular specification of Peyer patches in mice through determining endothelial addressin preference and may function as a susceptibility factor in inflammatory bowel diseases in humans. We wished to analyze the role of Nkx2.3 in colonic solitary intestinal lymphoid tissue composition and in colitis pathogenesis. We studied the colonic solitary intestinal lymphoid tissue of Nkx2.3-deficient mice with immunofluorescence and flow cytometry. Colitis was induced in mice using 2.5% dextran sodium sulfate, and severity was assessed with histology, flow cytometry, and quantitative PCR. We found that the lack of Nkx2.3 impairs maturation of isolated lymphoid follicles and attenuates dextran sodium sulfate-induced colitis independent of endothelial absence of mucosal addressin cell-adhesion molecule-1 (MAdCAM-1), which was also coupled with enhanced colonic epithelial regeneration. Although we observed increased numbers of group 3 innate lymphoid cells and Th17 cells and enhanced transcription of IL-22, Ab-mediated neutralization of IL-22 did not abolish the protection from colitis in Nkx2.3-deficient mice. Nkx2.3-/- hematopoietic cells could not rescue wild-type mice from colitis. Using LacZ-Nkx2.3 reporter mice, we found that Nkx2.3 expression was restricted to VAP-1+ myofibroblast-like pericryptal cells. These results hint at a previously unknown stromal role of Nkx2.3 as driver of colitis and indicate that Nkx2.3+ stromal cells play a role in epithelial cell homeostasis.

Nkx2-3-A Slippery Slope From Development Through Inflammation Toward Hematopoietic Malignancies

The development of peripheral lymphoid tissues from the mesoderm is the result of a complex convergence combining lymphohematopoietic differentiation with the local specification of nonhematopoietic mesenchymal components. Although the various transcriptional regulators with fate-determining effects in diversifying the mobile leukocyte subsets have been thoroughly studied and identified, the tissue-specific determinants promoting the regional differentiation of resident mesenchyme are less understood. Of these factors, various members of the NK-class Nkx paralogues have emerged as key regulators for the organogenesis of spleen and mucosal lymphoid tissues, and recent data have also indicated their involvement in various pathological events, including gut inflammation and hematopoietic malignancies. Here, we summarize available data on the roles of Nkx2-3 in lymphoid tissue development and discuss its possible value as a developmental marker and disease-associated pathogenic trait.

[Autoimmune encephalitis: possibilities in the laboratory investigation]

INTRODUCTION

The role of autoimmune responses against central nervous system (CNS) antigens in encephalitis presenting with non-classified neurologic or psychiatric symptoms has been appreciated in the past decade. Paraneoplastic limbic encephalitis has a poor prognosis and is most commonly associated with lung, ovarium, and testicular neoplasms, leading to immune reactions against intracellular antigens (anti-Hu/ANNA1, anti-Ri/ANNA2, anti-CV2/CRMP5 and anti-Ma2/Ta). In contrast, the recently described autoimmune encephalitis subtypes present with a broad spectrum of symptoms, respond to autoimmune therapies well and usually associate with autoantibodies against neuronal cell surface receptors (NMDAR, GABA_BR, AMPAR) or synaptic proteins (LGI1, CASPR2).

AIM

Our aim is to bring to awareness the increasing number of autoimmune encephalitis patients requiring neurologic, psychiatric and intensive care and to emphasize the significance of detecting various autoantibodies in diagnosing patients.

METHOD

In the past 6 years, our laboratory received 836 autoimmune encephalitis diagnostic test requests from a total of 717 patients. Serum and cerebrospinal fluid (CSF) samples were analysed with indirect immunofluorescence using a BIOCHIP consisting of cell lines transfected with 6 different receptor proteins.

RESULTS

IgG autoantibodies against receptor proteins were present in 7.5% of patients. The frequency of positive samples was the following: NMDAR > LGI1 > GABA_BR > CASPR2.

CONCLUSION

Detecting autoantibodies facilitates the diagnosis of autoimmune encephalitis in an early stage. Patients diagnosed early can be effectively treated with plasmapheresis and immunosuppressive drugs. The efficiency of therapies can be monitored by autoantibody detection. Therefore, the diagnostic immune laboratory plays an important role in proper diagnosis and in the prevention of rapidly progressing symptoms. Orv Hetil. 2018; 159(3): 107-112.

Innate lymphoid cells and their stromal microenvironments

In addition to the interaction between antigen presenting cells, T and B lymphocytes, recent studies have revealed important roles for a diverse set of auxiliary cells that profoundly influence the induction and regulation of immune responses against pathogens. Of these the stromal cells composed of various non-hematopoietic constituents are crucial for the creation and maintenance of specialized semi-static three-dimensional lymphoid tissue microenvironment, whereas the more recently described innate lymphoid cells are generated by the diversification of committed lymphoid precursor cells independently from clonally rearranged antigen receptor genes. Recent findings have revealed important contributions by innate lymphoid cells in inflammation and protection against pathogens in a tissue-specific manner. Importantly, lymphoid stromal cells also influence the onset of immune responses in tissue-specific fashion, raising the possibility of tissue-specific stromal - innate lymphoid cell collaboration. In this review we summarize the main features and interactions between these two cells types, with particular emphasis on ILC type 3 cells and their microenvironmental partners.

Reduced non-switched memory B cell subsets cause imbalance in B cell repertoire in systemic sclerosis

OBJECTIVES

Analysis of peripheral blood B lymphocytes in patients with systemic sclerosis (SSc) has provided evidence for specific alterations in naive and memory B cell balance. However, memory B cell subsets in SSc have not been thoroughly investigated. This study sought to identify phenotypic abnormalities and activation markers in peripheral blood memory B cells in SSc subtypes.

METHODS

Blood samples were obtained from 28 SSc patients with early form of disease (9 limited (lcSSc), 19 diffuse cutaneous SSc (dcSSc)) and 15 healthy controls. After magnetic bead separation of CD19+ B cells, multiparametric flow cytometry was performed and CD19+CD27- IgD+ naive, CD19+CD27+ memory, CD19+CD27+IgD+ non-switched memory CD19+CD27+IgD- switched memory, CD19+CD27-IgD- double negative (DN) memory, CD80+ or CD95+ activated cells were identified.

RESULTS

The proportion of naive B cells was higher (p=0.046) in SSc than in controls, with a decreased percentage of memory (p=0.018), especially non-switched memory B cells (p=0.015). The dcSSc patients had a significantly higher frequency of switched memory and DN memory B cells compared to lcSSc patients (p=0.025 and p=0.031). Percentage of CD95+CD27+ memory and CD95+ DN memory B cells was also significantly elevated in dcSSc compared to lcSSc patients (p=0.038 and p=0.045).

CONCLUSIONS

We conclude that the decreased proportion of memory B cells in SSc is due to reduction of non- switched memory B cells, resulting in an imbalance between the tolerogenic and activated memory B cell types. Elevated switched and activated CD95+ DN memory B cells may serve as a biomarker for dcSSc and can have a pathogenic potential by cytokine and autoantibody production.

Isolation and Characterization of a Murine Spontaneous High-Grade Follicular Lymphoma with Restricted In Vivo Spreading--a Model for Lymphatic Metastasis Via the Mesentery

Spontaneous or induced malignant lymphomas in mice are valuable tools for studying human lymphoproliferative diseases, including the mechanism of migration between peripheral lymphoid organs and positioning within distinct tissue compartments. Here we report the isolation and characterization of a novel spontaneous lymphoma from BALB/c mice showing restricted tissue distribution and metastasis. The lymphoma cells display CD19, B220, MHC II, surface IgG2a/kappa chain with VH7183 rearrangement of the IgH gene, indicating their B-cell origin. Serial intraperitoneal injection of primary tumor into both BALB/c and RAG-1-deficient hosts led to the successful propagation of lymphoma. Despite the cytological characteristics of high-grade follicular B-cell lymphoma, the tumor cells (denoted as Bc-DLFL.1) showed significantly lesser spreading to extraabdominal locations upon intraperitoneal passage compared to splenic and mesenteric lymph node expansion. In mesenteric lymph nodes the high endothelial venules contained only few tumor cells, while the lymphatic vessels were almost completely filled with lymphoma cells. Similarly, the LYVE-1-positive lymphatic capillaries within the mesentery were packed with lymphoma cells. These findings suggest that Bc-DLFL.1 cells likely propagate primarily via the lymphatic circulation within the mesentery, therefore this tumor may offer an in vivo model to investigate the tumor cell migration via the lymphatic circulation from the peritoneal cavity.

Divergence of Vascular Specification in Visceral Lymphoid Organs-Genetic Determinants and Differentiation Checkpoints

Despite their functional similarities, peripheral lymphoid tissues are remarkably different according to their developmental properties and structural characteristics, including their specified vasculature. Access of leukocytes to these organs critically depends on their interactions with the local endothelium, where endothelial cells are patterned to display a restricted set of adhesion molecules and other regulatory compounds necessary for extravasation. Recent advances in high throughput analyses of highly purified endothelial subsets in various lymphoid tissues as well as the expansion of various transgenic animal models have shed new light on the transcriptional complexities of lymphoid tissue vascular endothelium. This review is aimed at providing a comprehensive analysis linking the functional competence of spleen and intestinal lymphoid tissues with the developmental programming and functional divergence of their vascular specification, with particular emphasis on the transcriptional control of endothelial cells exerted by Nkx2.3 homeodomain transcription factor.

Tissue-specific impairment of stress hematopoiesis and megakaryocytopoiesis in mice deficient for Nkx2-3 homeodomain transcription factor (HEM5P.230)

Beside its several immunological roles, the spleen functions as an accessory hemopoetic tissue. This activity is restricted to the red pulp, which is influenced by transcription factor Nkx2-3. It is not yet known how the absence of Nkx2-3 affects the inducible splenic hemopoesis. In this work we studied how Nkx2-3 affects splenic stress hemopoiesis after inducing acute anemia and forced megakaryocyte differentiation using TPO-receptor agonist N-plate treatment. In untreated Nkx2-3 deficient mice the Ter119 erythroid cell frequency was higher in the bone marrow than in BALB/c controls, but it was lower in the spleen. Following anemization the number of erythroid cells increased in the bone marrow and spleen of BALB/c mice, whereas in Nkx2-3 KO mice erythroid expansion was only observed in the bone marrow, the splenic Ter119-positive erythroid compartment further decreased. The serum erythropoietin level increased in both groups and the highest level was in the anemic Nkx2-3 knockout group. Treatment with N-plate increased megakaryocyte number in wild-type BALB/c mice in both the bone marrow and spleen whereas in Nkx2-3 KO mice the spleen was resistant. These results show that Nkx2-3 plays a crucial role in the development of splenic stromal microenvironment necessary for supporting the extramedullary hematopoiesis in a tissue-specific manner.

Absence of Nkx2-3 homeodomain transcription factor reprograms the endothelial addressin preference for lymphocyte homing in Peyer's patches

Although the homing of lymphocytes to GALT has been extensively studied, little is known about how high endothelial venules (HEVs) within Peyer's patches (PPs) are patterned to display dominantly mucosal addressin cell adhesion molecule 1 (MAdCAM-1). In this study, we report that Nkx2-3-deficient mice show gradual loss of MAdCAM-1 in PPs postnatally and increased levels of mRNA for peripheral lymph node addressin (PNAd) backbone proteins as well as enhanced expression of MECA79 sulfated glycoepitope at the luminal aspect of HEVs, thus replacing MAdCAM-1 with PNAd. Induction of PNAd in mutant PPs requires lymphotoxin β receptor activity, and its upregulation needs the presence of mature T and B cells. Furthermore, treatment with MECA-79 anti-PNAd mAb in vivo effectively blocks lymphocyte homing to mutant PPs. Despite the replacement of MAdCAM-1 by PNAd in HEV endothelia, lymphocytes could efficiently home to PPs in mutant mice. We conclude that although Nkx2-3 activity controls the addressin balance of HEVs in GALT, the general HEV functionality is preserved independently from Nkx2-3, indicating a substantial plasticity in the specification of GALT HEV endothelium.

Marginal Zone Macrophage Receptor MARCO Is Trapped in Conduits Formed by Follicular Dendritic Cells in the Spleen

The marginal zone (MZ) region of the spleen plays an important role in leukocyte traffic and the removal of blood-borne pathogens by resident macrophages. Macrophage receptor with a collagenous structure (MARCO), expressed by MZ macrophages, recognizes several microbial ligands and is also involved in the retention of MZ B cells. Here, we report that MARCO is also associated with follicular dendritic cells (FDCs) in the spleen. In its FDC-associated form MARCO is arranged in 0.3-0.5-μm diameter granular-fibrillar structures with an appearance similar to the white pulp conduit system formed by fibroblastic reticular cells (FRCs), but with different compartment preference. The follicular display of MARCO resists irradiation and requires the presence of both MZ macrophages and differentiated FDCs. The follicular delivery of MARCO is independent from the shuffling of marginal zone B cells, and it persists after clodronate liposome-mediated depletion of MZ macrophages. Our findings thus indicate that MARCO is distributed to both MZ and follicles within the spleen into conduit-like structures, where FDC-bound MARCO may mediate communication between the stromal microenvironments of MZ and follicles.

Follicles in gut-associated lymphoid tissues create preferential survival niches for follicular Th cells escaping Thy-1-specific depletion in mice

Although a substantial number of T cells may escape depletion following in vivo mAb treatment in patients undergoing immunosuppression, their specific tissue location and phenotypic characteristics in different peripheral lymphoid tissues have not been analyzed in detail. Here we investigated the survival of CD4(+) T cells immediately following anti-Thy-1 mAb treatment in mice. We found a preferential survival of CD4(+) T cells expressing Thy-1 antigen in the Peyer's patches (PP) and also in mesenteric lymph nodes (MLN), where the relative majority of the surviving CD4(+) T cells displayed CD44(high)/CD62L(-) phenotype corresponding to effector memory T-cell features. These CD4(+) T cells also expressed CXCR5 and PD-1 (programmed cell death-1) markers characteristic for follicular Th cells (TFH). We also demonstrate that the immediate survival of these cells does not involve proliferation and is independent of IL-7. Induction of germinal center formation in spleen enhanced while the dissolution of follicular architecture by lymphotoxin-β receptor antagonist treatment slightly reduced TFH survival. Our results thus raise the possibility that the follicles within PP and MLN may create natural support niches for the preferential survival of TFH cells of the memory phenotype, thus allowing their escape during T-cell depletion.

Absence of Nkx2-3 homeodomain transcription factor induces the formation of LYVE-1-positive endothelial cysts without lymphatic commitment in the spleen

In contrast to peripheral lymph nodes possessing lymphatic and blood vasculature, the spleen in both humans and rodents is largely devoid of functioning lymphatic capillaries. Here it is reported that in mice lacking homeodomain transcription factor Nkx2-3, the spleen contains an extensive network of lymphocyte-filled sacs lined by cells expressing LYVE-1 antigen, a marker associated with lymphatic endothelium cells (LECs). Real-time quantitative PCR analyses of Nkx2-3 mutant spleen revealed a substantial increase of LYVE-1 and podoplanin mRNA levels, without the parallel increase of mRNA for VEGFR-3 (vascular endothelial growth factor receptor Type 3) and Prox1 (Prospero homeobobox protein 1), two markers specific for LECs. Although these structures express VEGFR-2/flk-1, they lack Prox1 protein, indicating their non-LEC endothelial origin. The LYVE-1(+) structures are bordered with ER-TR7(+) fibroblastic reticular cells with small clusters of macrophages expressing MARCO and sialoadhesin. Short-term cell-tracing studies using labeled lymphocytes indicate that these LYVE-1(+) cysts are largely excluded from the systemic circulation. Cells expressing LYVE-1 glycoprotein as putative precursors for such structures are detectable in the spleen of late-stage embryos, and the formation of LYVE-1(+) structures is independent from the activity of lymphotoxin β-receptor. Thus the splenic vascular defects in Nkx2-3 deficiency include the generation of LYVE-1(+) cysts, comprised of endothelial cells without being committed along the LEC lineage.

Transcription factor Nkx2-3 controls the vascular identity and lymphocyte homing in the spleen

The vasculature in the spleen and peripheral lymph nodes (pLNs) is considerably different, which affects both homing of lymphocytes and antigenic access to these peripheral lymphoid organs. In this paper, we demonstrate that in mice lacking the homeodomain transcription factor Nkx2-3, the spleen develops a pLN-like mRNA expression signature, coupled with the appearance of high endothelial venules (HEVs) that mediate L-selectin-dependent homing of lymphocytes into the mutant spleen. These ectopic HEV-like vessels undergo postnatal maturation and progressively replace MAdCAM-1 by pLN addressin together with the display of CCL21 arrest chemokine in a process that is reminiscent of HEV formation in pLNs. Similarly to pLNs, development of HEV-like vessels in the Nkx2-3-deficient spleen depends on lymphotoxin-β receptor-mediated signaling. The replacement of splenic vessels with a pLN-patterned vasculature impairs the recirculation of adoptively transferred lymphocytes and reduces the uptake of blood-borne pathogens. The Nkx2-3 mutation in BALB/c background causes a particularly disturbed splenic architecture, characterized by the near complete lack of the red pulp, without affecting lymph nodes. Thus, our observations reveal that the organ-specific patterning of splenic vasculature is critically regulated by Nkx2-3, thereby profoundly affecting the lymphocyte homing mechanism and blood filtering capacity of the spleen in a tissue-specific manner.