Multipotential acceptance of Peyer's patches in the intestine for both thymus-derived T cells and extrathymic T cells in mice

Crohn's disease as the intestinal manifestation of pan-lymphatic dysfunction: An exploratory proposal based on basic and clinical data

Crohn's disease (CD) is caused by immune, environmental, and genetic factors. It can involve the entire gastrointestinal tract, and although its prevalence is rapidly increasing its etiology remains unclear. Emerging biological and small-molecule drugs have advanced the treatment of CD; however, a considerable proportion of patients are non-responsive to all known drugs. To achieve a breakthrough in this field, innovations that could guide the further development of effective therapies are of utmost urgency. In this review, we first propose the innovative concept of pan-lymphatic dysfunction for the general distribution of lymphatic dysfunction in various diseases, and suggest that CD is the intestinal manifestation of pan-lymphatic dysfunction based on basic and clinical preliminary data. The supporting evidence is fully summarized, including the existence of lymphatic system dysfunction, recognition of the inside-out model, disorders of immune cells, changes in cell plasticity, partial overlap of the underlying mechanisms, and common gut-derived fatty and bile acid metabolism. Another benefit of this novel concept is that it proposes adopting the zebrafish model for studying intestinal diseases, especially CD, as this model is good at presenting and mimicking lymphatic dysfunction. More importantly, the ensuing focus on improving lymphatic function may lead to novel and promising therapeutic strategies for CD.

Assessing acute colitis induced by dextran sulfate sodium in rats and its impact on gastrointestinal fluids

Dextran sulfate sodium (DSS) is commonly used to induce colitis in rats. While the DSS-induced colitis rat model can be used to test new oral drug formulations for the treatment of inflammatory bowel disease, the effect of the DSS treatment on the gastrointestinal tract has not been thoroughly characterized. Additionally, the use of different markers to assess and confirm successful induction of colitis is somewhat inconsistent. This study aimed to investigate the DSS model to improve the preclinical evaluation of new oral drug formulations. The induction of colitis was evaluated based on the disease activity index (DAI) score, colon length, histological tissue evaluation, spleen weight, plasma C-reactive protein, and plasma lipocalin-2. Furthermore, the study investigated how the DSS-induced colitis affected the luminal pH, lipase activity, and concentrations of bile salts, polar lipids, and neutral lipids. For all evaluated parameters, healthy rats were used as a reference. The DAI score, colon length, and histological evaluation of the colon were effective disease indicators in DSS-induced colitis rats, while spleen weight, plasma C-reactive protein, and plasma lipocalin-2 were not. The luminal pH of the colon and bile salt- and neutral lipid concentrations in regions of the small intestine were lower in DSS-induced rats compared to healthy rats. Overall, the colitis model was deemed relevant for investigating ulcerative colitis-specific formulations.

The Role of the Lymphatic System in the Pathogenesis and Treatment of Inflammatory Bowel Disease

Although the number of therapeutic options for the treatment of inflammatory bowel disease (IBD) has increased in recent years, patients suffer from decreased quality of life due to non-response or loss of response to the currently available treatments. An increased understanding of the disease’s etiology could provide novel insights for treatment strategies in IBD. Lymphatic system components are generally linked to immune responses and presumably related to inflammatory diseases pathophysiology. This review aims to summarize findings on immune-mediated mechanisms in lymphoid tissues linked with IBD pathogenesis and (potential) novel treatments. Enhanced innate and adaptive immune responses were observed in mesenteric lymph nodes (MLNs) and other lymphoid structures, such as Peyer’s patches, in patients with IBD and in animal models. Furthermore, the phenomenon of lymphatic obstruction in the form of granulomas in MLNs and lymphatic vessels correlates with disease activity. There is also evidence that abnormalities in the lymphatic stromal components and lymph node microbiome are common in IBD and could be exploited therapeutically. Finally, novel agents targeting lymphocyte trafficking have been added to the treatment armamentarium in the field of IBD. Overall, gut-associated lymphoid tissue plays a key role in IBD immunopathogenesis, which could offer novel therapeutic targets.

The α4β1 Homing Pathway Is Essential for Ileal Homing of Crohn's Disease Effector T Cells In Vivo

BACKGROUND

The precise mechanisms controlling homing of T effector (Teff) cells to the inflamed gut in Crohn's disease (CD) are still unclear, and clinical outcome data from patients with inflammatory bowel disease treated with the anti-α4β7 integrin antibody vedolizumab suggest differences between ulcerative colitis and CD.

METHODS

Expression of homing molecules was studied with flow cytometry and immunohistochemistry. Their functional role was investigated in in vitro adhesion assays and in a humanized mouse model of T cell homing to the inflamed gut in vivo.

RESULTS

Despite in vitro blockade of CD Teff adhesion to mucosal vascular addressin cell adhesion molecule-1 (MadCAM-1) and in contrast to previous observations in ulcerative colitis, anti-α4β7 treatment did not result in reduced Teff cell homing to the colon in vivo. However, the integrin α4β1 was expressed in higher levels on Teffs from patients with CD compared with controls, while its expression in the peripheral blood declined, and its expression in the intestine increased during the course of clinical vedolizumab treatment. Consistently, adhesion of CD Teffs to vascular cell adhesion molecule-1 (VCAM-1) was blocked by inhibition of α4 and α4β1 in vitro. Moreover, in vivo homing of CD Teffs to the ileum was reduced by inhibition of α4 and α4β1 integrins, but not α4β7 integrins.

CONCLUSIONS

Our findings suggest that Teff cell homing to the ileum through the axis α4β1-VCAM-1 is an essential and nonredundant pathway in CD in vivo, possibly affecting efficacy of clinical treatment with antiadhesion compounds.

Dextran sulfate sodium-induced acute colitis impairs dermal lymphatic function in mice

AIM: To investigate whether dermal lymphatic function and architecture are systemically altered in dextran sulfate sodium (DSS)-induced acute colitis.

METHODS: Balb/c mice were administered 4% DSS in lieu of drinking water ad libitum for 7 d and monitored to assess disease activity including body weight, diarrhea severity, and fecal bleeding. Control mice received standard drinking water with no DSS. Changes in mesenteric lymphatics were assessed following oral administration of a fluorescently-labelled fatty acid analogue, while dermal lymphatic function and architecture was longitudinally characterized using dynamic near-infrared fluorescence (NIRF) imaging following intradermal injection of indocyanine green (ICG) at the base of the tail or to the dorsal aspect of the left paw prior to, 4, and 7 d after DSS administration. We also measured dye clearance rate after injection of Alexa680-bovine serum albumin (BSA). NIRF imaging data was analyzed to reveal lymphatic contractile activity after selecting fixed regions of interest (ROIs) of the same size in fluorescent lymphatic vessels on fluorescence images. The averaged fluorescence intensity within the ROI of each fluorescence image was plotted as a function of imaging time and the lymphatic contraction frequency was computed by assessing the number of fluorescent pulses arriving at a ROI.

RESULTS: Mice treated with DSS developed acute inflammation with clinical symptoms of loss of body weight, loose feces/watery diarrhea, and fecal blood, all of which were aggravated as disease progressed to 7 d. Histological examination of colons of DSS-treated mice confirmed acute inflammation, characterized by segmental to complete loss of colonic mucosa with an associated chronic inflammatory cell infiltrate that extended into the deeper layers of the wall of the colon, compared to control mice. In situ intravital imaging revealed that mice with acute colitis showed significantly fewer fluorescent mesenteric lymphatic vessels, indicating impaired uptake of a lipid tracer within mesenteric lymphatics. Our in vivo NIRF imaging data demonstrated dilated dermal lymphatic vessels, which were confirmed by immunohistochemical staining of lymphatic vessels, and significantly reduced lymphatic contractile function in the skin of mice with DSS-induced acute colitis. Quantification of the fluorescent intensity remaining in the depot as a function of time showed that there was significantly higher Alexa680-BSA fluorescence in mice with DSS-induced acute colitis compared to pre-treatment with DSS, indicative of impaired lymphatic drainage.

CONCLUSION: The lymphatics are locally and systemically altered in acute colitis, and functional NIRF imaging is useful for noninvasively monitoring systemic lymphatic changes during inflammation.

Local corticosterone production and angiotensin-I converting enzyme shedding in a mouse model of intestinal inflammation

AIM: To investigate local corticosterone production and angiotensin-I converting enzyme (ACE) protein expression and their interaction in healthy and inflamed intestine.

METHODS: Acute intestinal inflammation was induced to six weeks old male Balb/c mice by administration of either 3% or 5% dextran sodium sulfate (DSS) in drinking water for 7 d (n = 12 in each group). Healthy controls (n = 12) were given tap water. Corticosterone production and ACE protein shedding were measured from ex vivo incubates of the small and large intestine using EIA and ELISA, respectively. Morphological changes of the intestinal wall were assessed in hematoxylin-eosin stained tissue preparations of jejunum and distal colon. Effects of angiotensin II, captopril and metyrapone on corticosterone production was assessed by incubating pieces of small intestine of healthy mice in the presence of 0.1, 1 or 10 μmol/L angiotensin II, 1, 10 or 100 μmol/L captopril or 1, 10 or 100 μmol/L metyrapone solutions and measuring corticosterone released to the incubation buffer after 90 min (n = 5 in each group).

RESULTS: Both concentrations of DSS induced inflammation and morphological changes in large intestines but not in small intestines. Changes were observed as distortions of the crypt structure, mucosal erosion, immune cell infiltration to the mucosa and submucosal edema. Ex vivo corticosterone production (2.9 ± 1.0 ng/mL vs 2.0 ± 0.8 ng/mL, P = 0.034) and ACE shedding (269.2 ± 97.1 ng/mL vs 175.7 ± 52.2 ng/mL, P = 0.016) were increased in small intestines in 3% DSS group compared to the controls. In large intestine, corticosterone production was increased compared to the controls in both 3% DSS (229 ± 81 pg/mL vs 158 ± 30 pg/mL, P = 0.017) and 5% DSS groups (366 ± 163 pg/mL vs 158 ± 30 pg/mL, P = 0.002). Large intestine ACE shedding was increased in 5% DSS group (41.5 ± 9.0 ng/mL vs 20.9 ± 5.2 ng/mL, P = 0.034). Angiotensin II treatment augmented corticosterone production in small intestine at concentration of 10 μmol/L (0.97 ± 0.21 ng/mg protein vs 0.40 ± 0.09 ng/mg protein, P = 0.036).

CONCLUSION: Intestinal ACE shedding is increased by DSS-induced intestinal inflammation and parallels local corticosterone production. ACE product angiotensin II stimulates corticosterone formation in healthy intestine.

Colon irrigation causes lymphocyte movement from gut-associated lymphatic tissues to peripheral blood

It is well established that the intestine is an important site responsible for the local immune system. It is speculated that people suffering from constipation and carrying fecal residues in the intestine may have a decreased function of this immune system. In this study, colon irrigation, which is cleansing of the colon using a simple hydrotherapy instrument, was performed in 10 subjects with or without the disease. The number of leukocytes and their demarcation were then evaluated. The number and ratio of lymphocytes increased significantly after irrigation. This result suggested that colon irrigation might induce lymphocyte transmigration from gut-associated lymphatic tissues into the circulation, which may improve colon and immune system function.

Small-intestinal manifestations of dextran sulfate sodium consumption in rats and assessment of the effects of Lactobacillus fermentum BR11

The dextran sulfate sodium (DSS) colitis model has been utilized to screen for novel therapeutics for ulcerative colitis. Evidence suggests the small intestine may also be affected by DSS. We characterized the effects of DSS on the small intestine and assessed the potential for Lactobacillus fermentum BR11 to modify or normalize DSS-induced changes. Rats were allocated to three groups, Water + Vehicle, DSS + Vehicle, and DSS + L. fermentum BR11. BR11 was administered twice daily for 14 days. DSS (2%) was provided from days 7 to 14. Small-intestinal tissue was analyzed for sucrase activity, histology, and crypt cell proliferation. Increased ileum crypt depth and cell proliferation was observed in DSS-treated rats compared to controls (P < 0.05). BR11 normalized these parameters. While DSS predominantly induces colonic damage, minor morphological alterations were also detected in the distal small intestine. L. fermentum BR11 normalized these features.