Excision of mesenteric lymph nodes alters gut microbiota and impairs social dominance in adult mice

INTRODUCTION

Mesenteric lymph nodes (MLNs) are central in immune anatomy. MLNs are associated with the composition of gut microbiota, affecting the central system and immune system. Gut microbiota was found to differ among individuals of different social hierarchies. Nowadays, excision of MLNs is more frequently involved in gastrointestinal surgery; however, the potential side effects of excision of MLNs on social dominance are still unknown.

METHODS

MLNs were removed from male mice (7-8 weeks old). Four weeks after MLN removal, social dominance test was performed to investigate social dominance; hippocampal and serum interleukin (IL)-1β, IL-10, and tumor necrosis factor-alpha (TNF-α) were investigated; and histopathology was used to evaluate local inflammation of the ileum. The composition of the gut microbiota was then examined to understand the possible mechanism, and finally intraperitoneal injection of IL-10 was used to validate the effect of IL-10 on social dominance.

RESULTS

There was a decrease in social dominance in the operation group compared to the control group, as well as a decrease in serum and hippocampal IL-10 levels, but no difference in serum and hippocampal IL-1β and TNF-α levels, and no local inflammation of the ileum after MLN removal. 16S rRNA sequencing analysis showed that the relative abundance of the class Clostridia was decreased in the operation group. This decrease was positively associated with serum IL-10 levels. Furthermore, intraperitoneal injection of IL-10 in a subset of mice increased social dominance.

CONCLUSIONS

Our findings suggested that MLNs contributed to maintaining social dominance, which might be associated with reduced IL-10 and the imbalance of specific flora in gut microbiota.

Gut dysbiosis promotes the breakdown of oral tolerance mediated through dysfunction of mucosal dendritic cells

While dysbiosis in the gut is implicated in the impaired induction of oral tolerance generated in mesenteric lymph nodes (MesLNs), how dysbiosis affects this process remains unclear. Here, we describe that antibiotic-driven gut dysbiosis causes the dysfunction of CD11c⁺CD103⁺ conventional dendritic cells (cDCs) in MesLNs, preventing the establishment of oral tolerance. Deficiency of CD11c⁺CD103⁺ cDCs abrogates the generation of regulatory T cells in MesLNs to establish oral tolerance. Antibiotic treatment triggers the intestinal dysbiosis linked to the impaired generation of colony-stimulating factor 2 (Csf2)-producing group 3 innate lymphoid cells (ILC3s) for regulating the tolerogenesis of CD11c⁺CD103⁺ cDCs and the reduced expression of tumor necrosis factor (TNF)-like ligand 1A (TL1A) on CD11c⁺CD103⁺ cDCs for generating Csf2-producing ILC3s. Thus, antibiotic-driven intestinal dysbiosis leads to the breakdown of crosstalk between CD11c⁺CD103⁺ cDCs and ILC3s for maintaining the tolerogenesis of CD11c⁺CD103⁺ cDCs in MesLNs, responsible for the failed establishment of oral tolerance.

Predicting incomplete cytoreduction in patients with advanced ovarian cancer

Purpose

The most important prognostic factor for survival in ovarian cancer patients is complete cytoreduction. The preoperative prediction of suboptimal cytoreduction, considered as any residual disease at the end of surgery, could prevent futile surgery and morbidity. Here, we aimed to identify markers in the preoperative abdominal CT scans of an unselected cohort of patients with ovarian cancer that are predictive of incomplete cytoreduction.

Methods

This is a single-institution retrospective analysis of 105 epithelial ovarian cancer (EOC) patients treated with surgical cytoreduction between 2010 and 2020. Twenty-two variables on preoperative abdominal CT scans were compared to the intraoperative macroscopic findings by Fisher's exact test. Parameters with a significant correlation between intraoperative findings and imaging were analyzed by multivariate binary logistic regression analysis regarding the surgical outcome of complete versus incomplete cytoreduction.

Results

Complete cytoreduction (CC), indicated by the absence of macroscopic residual disease, was achieved in 79 (75.2%) of 105 patients and 46 (63.9%) of 72 International Federation of Gynecology and Obstetrics (FIGO) stage III and IV patients. Twenty patients (19%) were incompletely cytoreduced due to miliary carcinomatosis of the small bowel, and six patients (5.7%) had various locations of residual disease. Thirteen variables showed a significant correlation between imaging and surgical findings. Large-volume ascites, absence of numerically increased small lymph nodes at the mesenteric root, and carcinomatosis of the transverse colon in FIGO stage III and IV patients decreased the rate of CC to 26.7% in the multivariate analysis.

Conclusion

Large-volume ascites, the absence of numerically increased small lymph nodes at the mesenteric root, and carcinomatosis of the transverse colon are markers in preoperative CT scans predicting a low chance for complete cytoreduction in unselected ovarian cancer patients in a real-world setting.

Distribution of a highly lipophilic drug cannabidiol into different lymph nodes following oral administration in lipidic vehicle

Efficient delivery of highly lipophilic drugs or prodrugs to the mesenteric lymph nodes (MLN) can be achieved following oral administration with lipids. However, it remains unclear which specific MLN can be targeted and to what extent. Moreover, the efficiency of drug delivery to the retroperitoneal lymph nodes (RPLN) has not been assessed. The aim of this study was to assess the distribution of a highly lipophilic model drug cannabidiol (CBD), known to undergo intestinal lymphatic transport following administration with lipids, into specific MLN and RPLN in rats at various time-points post dosing. In vivo studies showed that at 2 hour following administration, significantly higher concentrations of CBD were present in the region second from the apex of the MLN chain. From 3 hours following administration, concentrations in all MLN were similar. CBD was also found at substantial levels in RPLN. This study demonstrates that drug concentrations in specific MLN are different, at least at the peak of the absorption process. Moreover, in addition to the MLN, the RPLN may also be targeted by oral route of administration, which may have further implications for treatment of a range of diseases.

Correlation between Structural Transformations in Mesenteric Lymph Nodes and the Levels MicroRNA during Polychemotherapy of Breast Cancer

We studied interrelationships between the cytoarchitectonics of the mesenteric lymph node and the levels of microRNA-21, microRNA-221/222, and microRNA-429 in the lymph, blood serum, and breast tissues in female Wistar rats with chemically induced breast cancer. After polychemotherapy, significant correlations were found between miRNA-221 and the number of lymphoblasts in the germinal centers and between miRNA-222 and the number of lymphoblasts in the germinal centers and macrophages in the medullary cords of the mesenteric lymph nodes.

Grape Seed Waste Counteracts Aflatoxin B1 Toxicity in Piglet Mesenteric Lymph Nodes

Aflatoxin B1 (AFB1) is a mycotoxin that frequently contaminates cereals and cereal byproducts. This study investigates the effect of AFB1 on the mesenteric lymph nodes (MLNs) of piglets and evaluates if a diet containing grape seed meal (GSM) can counteract the negative effect of AFB1 on inflammation and oxidative stress. Twenty-four weaned piglets were fed the following diets: Control, AFB1 group (320 μg AFB1/kg feed), GSM group (8% GSM), and AFB1 + GSM group (8% GSM + 320 μg AFB1/kg feed) for 30 days. AFB1 has an important antioxidative effect by decreasing the activity of catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) and total antioxidant status. As a result of the exposure to AFB1, an increase of MAP kinases, metalloproteinases, and cytokines, as effectors of an inflammatory response, were observed in the MLNs of intoxicated piglets. GSM induced a reduction of AFB1-induced oxidative stress by increasing the activity of GPx and SOD and by decreasing lipid peroxidation. GSM decreased the inflammatory markers increased by AFB1. These results represent an important and promising way to valorize this waste, which is rich in bioactive compounds, for decreasing AFB1 toxic effects in mesenteric lymph nodes.

Crohn's Disease: Is the Cold Chain Hypothesis Still Hot?

Crohn's disease [CD] is an inflammatory bowel disease of unknown aetiology. During recent decades, significant technological advances led to development of -omic datasets allowing a detailed description of the disease. Unfortunately these have not, to date, resolved the question of the aetiology of CD. Thus, it may be necessary to [re]consider hypothesis-driven approaches to resolve the aetiology of CD. According to the cold chain hypothesis, the development of industrial and domestic refrigeration has led to frequent exposure of human populations to bacteria capable of growing in the cold. These bacteria, at low levels of exposure, particularly those of the genus Yersinia, are believed to be capable of inducing exacerbated inflammation of the intestine in genetically predisposed subjects. We discuss the consistency of this working hypothesis in light of recent data from epidemiological, clinical, pathological, microbiological, and molecular studies.

Akkermansia muciniphila Exerts Lipid-Lowering and Immunomodulatory Effects without Affecting Neointima Formation in Hyperlipidemic APOE*3-Leiden.CETP Mice

SCOPE

Akkermansia muciniphila (A. muciniphila) is an intestinal commensal with anti-inflammatory properties both in the intestine and other organs. The aim is to investigate the effects of oral administration of A. muciniphila on lipid metabolism, immunity, and cuff-induced neointima formation in hyperlipidemic APOE*3-Leiden (E3L).CETP mice.

METHODS AND RESULTS

Hyperlipidemic male E3L.CETP mice are daily treated with 2 × 108 CFU A. muciniphila by oral gavage for 4 weeks and the effects are determined on plasma lipid levels, immune parameters, and cuff-induced neointima formation and composition. A. muciniphila administration lowers body weight and plasma total cholesterol and triglycerides levels. A. muciniphila influences the immune cell composition in mesenteric lymph nodes, as evident from an increased total B cell population, while reducing the total T cell and neutrophil populations. Importantly, A. muciniphila reduces the expression of the activation markers MHCII on dendritic cells and CD86 on B cells. A. muciniphila also increases whole blood ex vivo lipopolysaccharide-stimulated IL-10 release. Finally, although treatment with A. muciniphila improves lipid metabolism and immunity, it does not affect neointima formation or composition.

CONCLUSIONS

Four weeks of treatment with A. muciniphila exerts lipid-lowering and immunomodulatory effects, which are insufficient to inhibit neointima formation in hyperlipidemic E3L.CETP mice.

Structural and Functional Changes in the Mesenteric Lymph Nodes in Humans during Aging

Morphometric analysis of structural and functional changes in the human mesenteric lymph nodes during aging revealed the development of fibrous connective tissue, fragmentation of the lymphoid parenchyma, the absence of follicles with germinal centers, and a decrease in the level of lymphocyte proliferation, which was confirmed by the absence of Ki-67⁺ cells. The paracortical zone lacked CD4⁺ T helpers that regulate both cellular and humoral immunity. High content of plasma cells and eosinophilic granulocytes in the medullary cords and sinuses reflects the development of autoimmune processes associated with a decrease in the number of regulatory T lymphocytes. The development of fibrous connective tissue in the sinus system complicates lymph flow through the lymph node and impairs lymph filtration.

Differential Roles of Dendritic Cells in Expanding CD4 T Cells in Sepsis

Sepsis is a systemically dysregulated inflammatory syndrome, in which dendritic cells (DCs) play a critical role in coordinating aberrant immunity. The aim of this study is to shed light on the differential roles played by systemic versus mucosal DCs in regulating immune responses in sepsis. We identified a differential impact of the systemic and mucosal DCs on proliferating allogenic CD4 T cells in a mouse model of sepsis. Despite the fact that the frequency of CD4 T cells was reduced in septic mice, septic mesenteric lymph node (MLN) DCs proved superior to septic spleen (SP) DCs in expanding allogeneic CD4 T cells. Moreover, septic MLN DCs markedly augmented the surface expression of MHC class II and CD40, as well as the messaging of interleukin-1β (IL-1β). Interestingly, IL-1β-treated CD4 T cells expanded in a dose-dependent manner, suggesting that this cytokine acts as a key mediator of MLN DCs in promoting septic inflammation. Thus, mucosal and systemic DCs were found to be functionally different in the way CD4 T cells respond during sepsis. Our study provides a molecular basis for DC activity, which can be differential in nature depending on location, whereby it induces septic inflammation or immune-paralysis.

Differential Pathogenic Th17 Profile in Mesenteric Lymph Nodes of Crohn's Disease and Ulcerative Colitis Patients

The drug targets IL23 and IL12 regulate pathogenicity and plasticity of intestinal Th17 cells in Crohn's disease (CD) and ulcerative colitis (UC), the two most common inflammatory bowel diseases (IBD). However, studies examining Th17 dysregulation in mesenteric lymph nodes (mLNs) of these patients are rare. We showed that in mLNs, CD could be distinguished from UC by increased frequencies of CCR6⁺CXCR3⁻RORγ⁺Tbet⁻CD4⁺ (Th17) memory T cells enriched in CD62L^low effector memory T cells (T_EM), and their differentially expressed molecular profile. Th17 T_EM cells (expressing IL17A, IL17F, RORC, and STAT3) displayed a higher pathogenic/cytotoxic (IL23R, IL18RAP, and GZMB, CD160, PRF1) gene signature in CD relative to UC, while non-pathogenic/regulatory genes (IL9, FOXP3, CTLA4) were more elevated in UC. In both CD and UC, IL12 but not IL23, augmented IFNγ expression in Th17 T_EM and switched their molecular profile toward an ex-Th17 (Th1^*)-biased transcriptomic signature (increased IFNG, and decreased TCF7, IL17A), suggesting that Th17 plasticity occurs in mLNs before their recruitment to inflamed colon. We propose that differences observed between Th17 cell frequencies and their molecular profile in CD and UC might have implications in understanding disease pathogenesis, and thus, therapeutic management of patients with IBD.

Impaired IL-17 Production in Gut-Residing Immune Cells of 5xFAD Mice with Alzheimer's Disease Pathology

Alzheimer's disease (AD) is characterized by accumulation of amyloid-β plaques that further promotes microglia-mediated neuroinflammatory responses and inflammation in the brain. Emerging data are revealing the relation between gut-associated lymphoid tissue (GALT) cells and CNS, as effector cells primed in the gut might home to the brain. This study aimed to determine cell composition of GALT in 5xFAD mice, an established model for AD. Immune cells isolated from Peyer's patches (PP) and mesenteric lymph nodes (MLN) were stained with surface and intracellular markers for T helper (Th) subpopulations, B lymphocytes and macrophages and analyzed cytofluorimetrically, while cytokine expression and production were determined by qPCR and ELISA, respectively. Inflammation was detected in GALT of 5xFAD mice with established AD pathology. Although the production of IFN-γ, IL-4, and IL-10 was comparable between the strains, lower IL-17 production was observed in PP and MLN cells. This phenomenon could not be attributed to a lower abundance of Th17 cells, or cytokines that initiate their formation or propagation (TGF-β, IL-6, and IL-23). Also, reduced IL-17 production was not a consequence of altered Il-17 mRNA transcription or deficiency of Rorγt, a key transcription factor for IL-17. However, the expression of miR-155 (a non-coding micro RNA that promotes the development of Th17 cells), was significantly lower in MLN cells of 5xFAD mice. In contrast, mice without AD neuropathology did not have inflammation in GALT or altered Th17 numbers, nor decreased IL-17 production. In conclusion, the observed changes in GALT of 5xFAD mice mirror the disease progression and might reflect inadequate immune surveillance in the gut and lead to enhanced AD pathology.

The Human Mesenteric Lymph Node Microbiome Differentiates Between Crohn's Disease and Ulcerative Colitis

BACKGROUND AND AIMS

Mesenteric lymph nodes are sites in which translocated bacteria incite and progress immunological responses. For this reason, understanding the microbiome of mesenteric lymph nodes in inflammatory bowel disease is important. The bacterial profile of Crohn's disease mesenteric lymph nodes has been analysed using culture-independent methods in only one previous study. This study aimed to investigate the mesenteric lymph node microbiota from both Crohn's disease and ulcerative colitis patients.

METHODS

Mesenteric lymph nodes were collected from Crohn's disease and ulcerative colitis patients undergoing resection. Total DNA was extracted from mesenteric lymph nodes and assessed for the presence of bacterial DNA [16S]. All work was completed in a sterile environment using aseptic techniques. Samples positive for 16S DNA underwent next-generation sequencing, and the identity of bacterial phyla and species were determined.

RESULTS

Crohn's disease mesenteric lymph nodes had a distinctly different microbial profile to that observed in ulcerative colitis. The relative abundance of Firmicutes was greater in nodes from ulcerative colitis patients, whereas Proteobacteria were more abundant in Crohn's disease. Although species diversity was reduced in the mesenteric lymph nodes of patients with Crohn's disease, these lymph nodes contained greater numbers of less dominant phyla, mainly Fusobacteria.

CONCLUSION

This study confirms that there are distinct differences between the Crohn's disease and ulcerative colitis mesenteric lymph node microbiomes. Such microbial differences could aid in the diagnosis of Crohn's disease or ulcerative colitis, particularly in cases of indeterminate colitis at time of resection, or help explain their mechanisms of development and progression.

Inflammatory Mediators in the Mesenteric Lymph Nodes, Site of a Possible Intermediate Phase in the Immune Response to Feline Coronavirus and the Pathogenesis of Feline Infectious Peritonitis?

Feline infectious peritonitis (FIP) is an almost invariably fatal feline coronavirus (FCoV)-induced disease thought to arise from a combination of viral mutations and an overexuberant immune response. Natural initial enteric FCoV infection may remain subclinical, or result in mild enteric signs or the development of FIP; cats may also carry the virus systemically with no adverse effect. This study screened mesenteric lymph nodes (MLNs), the presumed first site of FCoV spread from the intestine regardless of viraemia, for changes in the transcription of a panel of innate immune response mediators in response to systemic FCoV infection and with FIP, aiming to identify key pathways triggered by FCoV. Cats with and without FIP, the latter with and without FCoV infection in the MLN, were compared. Higher expression levels in FIP were found for toll-like receptors (TLRs) 2, 4 and 8. These are part of the first line of defence and suggest a response to both viral structural proteins and viral nucleic acid. Expression of genes encoding inflammatory cytokines and chemokines, including interleukin (IL)-1β, IL-6, IL-15, tumour necrosis factor (TNF)-α, CXCL10, CCL8, interferon (IFN)-α, IFN-β and IFN-γ, was higher in cats with FIP, consistent with inflammatory pathway activation. Expression of genes encoding transcription factors STAT1 and 2, regulating signalling pathways, particularly of the interferons, was also higher. Among cats without FIP, there were few differences between virus-positive and virus-negative MLNs; however, TLR9 and STAT2 expression were higher with infection, suggesting a direct viral effect. The study provides evidence for TLR involvement in the response to FCoV. This could open up new avenues for therapeutic approaches.

Impact of CCR7 on T-Cell Response and Susceptibility to Yersinia pseudotuberculosis Infection

Background

To successfully limit pathogen dissemination, an immunological link between the entry tissue of the pathogen and the underlying secondary lymphoid organs (SLOs) needs to be established to prime adaptive immune responses. Here, the prerequisite of CCR7 to mount host immune responses within SLOs during gastrointestinal Yersinia pseudotuberculosis infection to limit pathogen spread was investigated.

Methods

Survival, bacterial dissemination, and intestinal and systemic pathology of wild-type and CCR7-/- mice were assessed and correlated to the presence of immune cell subsets and cytokine responses throughout the course of infection.

Results

The CCR7-/- mice show a significantly higher morbidity and are more prone to pathogen dissemination and intestinal and systemic inflammation during the oral route of infection. Significant impact of CCR7 deficiency over the course of infection on several immunological parameters were observed (ie, elevated neutrophil-dominated innate immune response in Peyer's patches, limited dendritic cell migration to mesenteric lymph nodes [mLNs] causing reduced T cell-mediated adaptive immune responses (in particular Th17-like responses) in mLNs).

Conclusions

Our work indicates that CCR7 is required to mount a robust immune response against enteropathogenic Y. pseudotuberculosis by promoting Th17-like responses in mLNs.

Distinct DC subsets regulate adaptive Th1 and 2 responses during Trichuris muris infection

Low- and high-dose infections with the murine large intestinal nematode Trichuris muris are associated with induction of adaptive Th1 and Th2 responses, respectively, in mesenteric lymph nodes (MLN). Classical dendritic cells (cDC) accumulate in the large intestinal mucosa and MLN upon T. muris infection, yet their role in driving adaptive responses to infection remains largely unknown. We performed low- and high-dose T. muris infections of mice deficient in defined cDC subsets to investigate their role in induction of adaptive immune responses. Mice lacking IRF4-dependent cDC failed to clear a high-dose infection and displayed impaired Th2 responses. Conversely, mice lacking IRF8-dependent cDC cleared a low-dose infection and displayed an impaired Th1 response while increased production of Th2 cytokines. Finally, mice lacking both IRF4- and IRF8-dependent cDC were able to generate a Th2 response and clear a low-dose infection. Collectively, these results suggest that IRF4- and IRF8-dependent cDC act antagonistically during T. muris infection, and demonstrate that intestinal Th2 responses can be generated towards T. muris in the absence of IRF4-dependent cDC.

Feeding a Mixture of Choline Forms during Lactation Improves Offspring Growth and Maternal Lymphocyte Response to Ex Vivo Immune Challenges

Study objectives were to examine the impact of feeding a mixture of choline forms, or a diet high in glycerophosphocholine (GPC) on maternal immune function and offspring growth during lactation. Lactating Sprague-Dawley rat dams (n = 6/diet) were randomized to one of three diets, providing 1 g/kg total choline: Control (100% free choline (FC)), Mixed Choline (MC; 50% phosphatidylcholine (PC), 25% FC, 25% GPC), or High GPC (HGPC; 75% GPC, 12.5% PC, 12.5% FC). At 3 weeks, cell phenotypes and cytokine production with Concanavalin A (ConA)-or lipopolysaccharide (LPS)-stimulated splenocytes and mesenteric lymphocytes were measured. Feeding MC or HGPC diets improved pups' growth compared to Control (+22% body weight, p < 0.05). In spleen, MC-and HGPC-fed dams had higher proportions of cytotoxic (CD8+) T cells expressing CD27, CD71 and CD127, total B cells (CD45RA+) and dendritic cells (OX6+OX62+), and produced less IL-6 and IFN-γ after ConA than Control-fed dams (p < 0.05). MC and HGPC LPS-stimulated splenocytes produced less IL-1β and IL-6 than Control. ConA-stimulated mesenteric lymphocytes from MC and HGPC dams produced more IL-2 and IFN-γ than Control (p < 0.05). In summary, feeding a mixture of choline forms during lactation improved offspring growth and resulted in a more efficient maternal immune response following mitogenic immune challenge.

CD169 Expressing Macrophage, a Key Subset in Mesenteric Lymph Nodes Promotes Mucosal Inflammation in Dextran Sulfate Sodium-Induced Colitis

Inflammatory bowel disease (IBD) including Crohn’s disease (CD) and ulcerative colitis is a relapsing-remitting illness. Patients with long-standing extensive colitis are easy to develop colorectal cancer (CRC). The increasing incidence of IBD and a substantial increase in the risk of CRC make the necessity to pay more attention on the regulation of inflammation especially by specific macrophages subset. The present study reported that a key subset of sinus macrophage expressing CD169 in mesenteric lymph nodes (mLNs) played an essential role in promoting mucosal inflammation. The results revealed that the subset expressing CD169 in mLNs increased significantly during the dextran sulfate sodium (DSS)-induced colitis. The colitic symptoms were alleviated in CD169-diphtheria toxin receptor (DTR) mice at least partially due to the deletion of CD169⁺ macrophages in mLNs. In addition, the levels of inflammatory cytokines as well as the percentage of Th17 cells in mLNs from CD169-DTR mice were much lower than those from WT mice with DSS-induced colitis. Further experiment in vitro demonstrated that the supernatant from whole cells of mLNs or colon tissues could promote the production of inflammatory factors by mLN cells or colon tissues from CD169-DTR mice. These results could be explained by the cell sorting result that CD11b⁺CD169⁺ macrophages expressed higher level of inflammatory factors directly. All these data indicated that CD169⁺ sinus macrophage in mLNs played an essential role on regulating mucosal inflammation.

Mesenteric lymph node CD11b- CD103+ PD-L1High dendritic cells highly induce regulatory T cells

Dendritic cells (DCs) in mesenteric lymph nodes (MLNs) induce Foxp3⁺ regulatory T cells to regulate immune responses to beneficial or non-harmful agents in the intestine, such as commensal bacteria and foods. Several studies in MLN DCs have revealed that the CD103⁺ DC subset highly induces regulatory T cells, and another study has reported that MLN DCs from programmed death ligand 1 (PD-L1) -deficient mice could not induce regulatory T cells. Hence, the present study investigated the expression of these molecules on MLN CD11c⁺ cells. Four distinct subsets expressing CD103 and/or PD-L1 were identified, namely CD11b⁺ CD103⁺ PD-L1^High , CD11b^- CD103⁺ PD-L1^High , CD11b^- CD103⁺ PD-L1^Low and CD11b⁺ CD103^- PD-L1^Int . Among them, the CD11b^- CD103⁺ PD-L1^High DC subset highly induced Foxp3⁺ T cells. This subset expressed Aldh1a2 and Itgb8 genes, which are involved in retinoic acid metabolism and transforming growth factor-β (TGF-β) activation, respectively. Exogenous TGF-β supplementation equalized the level of Foxp3⁺ T-cell induction by the four subsets whereas retinoic acid did not, which suggests that high ability to activate TGF-β is determinant for the high Foxp3⁺ T-cell induction by CD11b^- CD103⁺ PD-L1^High DC subset. Finally, this subset exhibited a migratory DC phenotype and could take up and present orally administered antigens. Collectively, the MLN CD11b^- CD103⁺ PD-L1^High DC subset probably takes up luminal antigens in the intestine, migrates to MLNs, and highly induces regulatory T cells through TGF-β activation.

The Tat Substrate SufI Is Critical for the Ability of Yersinia pseudotuberculosis To Cause Systemic Infection

The twin arginine translocation (Tat) system targets folded proteins across the inner membrane and is crucial for virulence in many important human-pathogenic bacteria. Tat has been shown to be required for the virulence of Yersinia pseudotuberculosis, and we recently showed that the system is critical for different virulence-related stress responses as well as for iron uptake. In this study, we wanted to address the role of the Tat substrates in in vivo virulence. Therefore, 22 genes encoding potential Tat substrates were mutated, and each mutant was evaluated in a competitive oral infection of mice. Interestingly, a ΔsufI mutant was essentially as attenuated for virulence as the Tat-deficient strain. We also verified that SufI was Tat dependent for membrane/periplasmic localization in Y. pseudotuberculosisIn vivo bioluminescent imaging of orally infected mice revealed that both the ΔsufI and ΔtatC mutants were able to colonize the cecum and Peyer's patches (PPs) and could spread to the mesenteric lymph nodes (MLNs). Importantly, at this point, neither the ΔtatC mutant nor the ΔsufI mutant was able to spread systemically, and they were gradually cleared. Immunostaining of MLNs revealed that both the ΔtatC and ΔsufI mutants were unable to spread from the initial infection foci and appeared to be contained by neutrophils, while wild-type bacteria readily spread to establish multiple foci from day 3 postinfection. Our results show that SufI alone is required for the establishment of systemic infection and is the major cause of the attenuation of the ΔtatC mutant.

Morphological Changes in Mesenteric Lymph Nodes and Lymphocyte Subpopulation Composition in Experimental Ulcerative Colitis

Morphological changes in the mesenteric lymph nodes of male C57Bl/6 mice and subpopulation composition of lymphocytes in these nodes were studied in experimental acute and chronic ulcerative colitis induced by sodium dextran sulfate. Acute and chronic ulcerative colitis was associated with the development of reactive changes in the mesenteric lymph nodes. These changes were of mixed type and were characterized by follicular hyperplasia and sinus reaction. The content of CD19(+) B cells in the mesenteric lymph nodes decreased in acute ulcerative colitis, while the content of CD3(+)CD8(+) cytotoxic T cells increased, which presumably reflected activation of Th1 reactions. The increase in the count of CD4(+)CD25(+)FOXP3(+) regulatory T cells and CD3(+)CD8(+) cytotoxic T cells was due to intensive migration of lymphocytes from the thymus and the colonic compartment of the local immune system. Chronic ulcerative colitis was associated with higher levels of CD19(+) B cells and CD3(+)CD4(+) T helper cells in the mesenteric lymph nodes, which was characteristic of adoptive immunity reactions and chronization of the inflammatory process.

Leukocyte populations and IL-6 in the tumor microenvironment of an orthotopic colorectal cancer model

Colorectal cancer (CRC) is a major health problem worldwide. It is often diagnosed late due to its asymptomatic nature. As with all cancers, an immune reaction is involved; however, in CRC, it is unknown if this immune response is favorable or unfavorable for disease progression. In this study, the immune response in mesenteric lymph nodes (MLNs) and Peyer's patches was investigated during development of CRC in an orthotopic mouse model. CRC was induced by injecting CT26 cells into the cecum wall of BALB/c mice. Flow cytometry was used to analyze leukocyte populations involved in tumor immunity in MLNs and Peyer's patches. Cryostat sections for immunohistochemistry were prepared from the caecum and colon from CRC-induced and sham-operated animals. Cytokines produced by mouse CT26 cell line were measuredin vitroandin vivo Significant increases in the number of CD8(+)/TCR(+)and CD49b(+)/TCR(-)(natural killer) cells were found in MLNs and Peyer's patches in the CRC group. In addition, γδT cells were present in the lamina propria of the colon tissues from sham-operated mice, but absent in the colon tissues from mice with CRC. Immunohistochemical analysis of tumorous tissues showed eosinophil, CD69(+)T cell, and CD11b(+)cell infiltration. Bothin vitroandin vivoCT26 tumor cells were interleukin (IL)-6 positive. In addition, tumor-infiltrating CD45(+)cells were also IL-6 positive. In summary, the kinetics of the immune response to CRC and the key effector lymphocytes that are implicated in tumor immunity are demonstrated. Furthermore, IL-6 is a key cytokine present within the tumor microenvironment.

Gut microbiota amplifies host-intrinsic conversion from the CD8 T cell lineage to CD4 T cells for induction of mucosal immune tolerance

Microbiota has been shown to promote tolerogenic differentiation of T lymphocytes. It remains unclear to what extent microbiota triggers de novo re-programming or amplify pre-existing plasticity intrinsic to T cells. In a study with mouse models to track the clonal fate of CD4 and CD8 T cells, we discovered that CD8 T cells converted to MHC class I-restricted CD4 T cells without regard to selfness of their antigen specificity. In mesenteric lymph nodes (MLN), CD8 T cells converted to CD4(+)Foxp3(+) regulatory T (Treg) cells which were enriched in the large intestine lamina propria (LILP) and suppressed chemical- or immune-mediated inflammatory damage. In germ-free conditions, the converted CD4 populations were present in MLN, but absent in LILP. Therefore, an intrinsic plasticity in the host was amplified by the gut microbiota, leading to selfless tolerance induction in the intestinal mucosa. The findings may be relevant to HIV infection, cancer and autoimmune disorders.

Mesenteric lymphadenitis caused by Yersinia enterocolitica

Yersiniosis is an acute or chronic, zoonotic disease caused by infection of Gram-negative rods Yersinia enterocolitica. It can be transmitted by the consumption of originally contaminated food products (pork, unpasteurized milk) or secondarily contaminated with animal or vegetable products. The clinical picture of infection may have a variable course is related to the age and physical condition of the patient, or pathogenic properties of microorganisms. Infection caused by Y. enterocolitica can occur in different clinical forms: food poisoning, colitis, mesentric lymphadenitis, erythema nodosum, arthritis, pharyngitis, pneumonia, meningitis, sepsis. The aim of this study was to present a rare case of infection with Y. enterocolitica mesenteric lymph nodes coexistent with appendicitis.

Atg16l1 is required for autophagy in intestinal epithelial cells and protection of mice from Salmonella infection

BACKGROUND & AIMS

Intestinal epithelial cells aid in mucosal defense by providing a physical barrier against entry of pathogenic bacteria and secreting antimicrobial peptides (AMPs). Autophagy is an important component of immune homeostasis. However, little is known about its role in specific cell types during bacterial infection in vivo. We investigated the role of autophagy in the response of intestinal epithelial and antigen-presenting cells to Salmonella infection in mice.

METHODS

We generated mice deficient in Atg16l1 in epithelial cells (Atg16l1(f/f) × Villin-cre) or CD11c(+) cells (Atg16l1(f/f) × CD11c-cre); these mice were used to assess cell type-specific antibacterial autophagy. All responses were compared with Atg16l1(f/f) mice (controls). Mice were infected with Salmonella enterica serovar typhimurium; cecum and small-intestine tissues were collected for immunofluorescence, histology, and quantitative reverse-transcription polymerase chain reaction analyses of cytokines and AMPs. Modulators of autophagy were screened to evaluate their effects on antibacterial responses in human epithelial cells.

RESULTS

Autophagy was induced in small intestine and cecum after infection with S typhimurium, and required Atg16l1. S typhimurium colocalized with microtubule-associated protein 1 light chain 3β (Map1lc3b or LC3) in the intestinal epithelium of control mice but not in Atg16l1(f/f) × Villin-cre mice. Atg16l1(f/f) × Villin-cre mice also had fewer Paneth cells and abnormal granule morphology, leading to reduced expression of AMPs. Consistent with these defective immune responses, Atg16l1(f/f) × Villin-cre mice had increased inflammation and systemic translocation of bacteria compared with control mice. In contrast, we observed few differences between Atg16l1(f/f) × CD11c-cre and control mice. Trifluoperazine promoted autophagy and bacterial clearance in HeLa cells; these effects were reduced upon knockdown of ATG16L1.

CONCLUSIONS

Atg16l1 regulates autophagy in intestinal epithelial cells and is required for bacterial clearance. It also is required to prevent systemic infection of mice with enteric bacteria.

IL-7 promotes long-term in vitro survival of unique long-lived memory subset generated from mucosal effector memory CD4+ T cells in chronic colitis mice

Colitogenic memory CD4(+) T cells are important in the pathogenesis of inflammatory bowel disease (IBD). Although memory stem cells with high survival and self-renewal capacity were recently identified in both mice and humans, it is unclear whether a similar subset is present in chronic colitis mice. We sought to identify and purify a long-lived subset of colitogenic memory CD4(+) T cells, which may be targets for treatment of IBD. A long-lived subset of colitogenic memory CD4(+) T cells was purified using a long-term culture system. The characteristics of these cells were assessed. Interleukin (IL)-7 promoted the in vitro survival for >8 weeks of lamina propria (LP) CD4(+) T cells from colitic SCID mice previously injected with CD4(+)CD45RB(high) T cells. These cells were in a quiescent state and divided a maximum of 5 times in 4 weeks. LP CD4(+) T cells expressed higher levels of Bcl-2, integrin-α4β7, CXCR3 and CD25 after than before culture, as well as secreting high concentrations of IL-2 and low concentrations of IFN-γ and IL-17 in response to intestinal bacterial antigens. LP CD4(+) T cells from colitic mice cultured with IL-7 for 8 weeks induced more severe colitis than LP CD4(+) T cells cultured for 4 weeks. We developed a novel culture system to purify a long-lived, highly pathogenic memory subset from activated LP CD4(+) T cells. IL-7 promoted long-term in vitro survival of this subset in a quiescent state. This subset will be a novel, effective target for the treatment of IBD.

β-Glucan microparticles are good candidates for mucosal antigen delivery in oral vaccination

Continuously improving the developmental process and the efficacy of oral vaccines is essential in the fight against intestinal pathogens. A promising strategy for vaccination applying safe, biodegradable and non-replicating antigen delivery systems has gained increased interest for eliciting cellular and humoral immune responses. The current study evaluates the potential of β-glucan particles (GP) as an oral antigen delivery system and their adjuvant characteristics. GP are efficiently internalized by human intestinal epithelial cell lines (Caco-2 and HT-29 cells), without exerting negative effects on cell viability. GP triggered the expression of pro-inflammatory cytokines IL-23p19, IL-8 and the β-glucan receptors dectin-1 and TLR2 by activated Caco-2 cells, and CCL20 in HT-29 cells. In contrast, the expression level of TGF-β, an important mediator of oral tolerance, was significantly downregulated in HT-29 cells. Additionally, adoptive transfer experiments showed proliferating ovalbumin (OVA)-specific CD4(+) T cells mainly in the spleens of GP-OVA-fed mice. Furthermore, we detected a significantly increased IL-17 and a trend towards increased IFN-γ production in the spleen of GP-OVA-fed mice upon antigen restimulation. Oral administration of GP-OVA induced increased OVA-specific IgA, secretory-IgA (S-IgA) and secretory component (SC) production in intestinal fluids. Our data show that GP vehicles are able to deliver OVA via an oral route allowing efficient antigen presentation alongside adaptive immune activation, resulting in a Th17-biased response and the production of OVA-specific IgA, secretory-IgA and secretory component antibodies.

Migratory conventional dendritic cells in the induction of peripheral T cell tolerance

Conventional DCs are an extremely heterogeneous cell population that comprises several different subsets. A major distinction can be made between lymphoid-resident DCs that are present in the lymphoid tissues and the blood and migratory DCs that reside in the nonlymphoid tissues and migrate to the lymph nodes, both in homeostatic conditions and during the course of an infection. Migratory DCs differ from tissue to tissue but share the unique ability to transport antigens to the draining lymph nodes-in particular, tissue-restricted antigens in homeostatic conditions and microbial antigens after an infection. Recently, steady-state migratory DCs have gained much attention after the discovery of their high tolerogenic potential. The purpose of this review is to give a picture of the recent finding regarding steady-state migratory DCs with particular interest in their role in inducing T cell tolerance.

A role for tumor necrosis factor receptor type 1 in gut-associated lymphoid tissue development: genetic evidence of synergism with lymphotoxin beta

Lymphotoxin alpha (LTalpha) signals via tumor necrosis factor receptors (TNFRs) as a homotrimer and via lymphotoxin beta receptor (LTbetaR) as a heterotrimeric LTalpha1beta2 complex. LTalpha-deficient mice lack all lymph nodes (LNs) and Peyer's patches (PPs), and yet LTbeta-deficient mice and TNFR-deficient mice have cervical and mesenteric LN. We now show that mice made deficient in both LTbeta and TNFR type 1 (TNFR1) lack all LNs, revealing redundancy or synergism between TNFR1 and LTbeta, acting presumably via LTbetaR. A complete lack of only PPs in mice heterozygous for both ltalpha and ltbeta, but not ltalpha or ltbeta alone, suggests a similar two-ligand phenomenon in PP development and may explain the incomplete lack of PPs seen in tnfr1-/- mice.