Lymph node stromal cells support dendritic cell-induced gut-homing of T cells.

T cells are imprinted to express tissue-specific homing receptors upon activation in tissue-draining lymph nodes, resulting in their migration to the site of Ag entry. Expression of gut-homing molecules alpha(4)beta(7) and CCR9 is induced by retinoic acid, a vitamin A metabolite produced by retinal dehydrogenases, which are specifically expressed in dendritic cells as well as stromal cells in mucosa-draining lymph nodes. In this study, we demonstrate that mesenteric lymph node stromal cell-derived retinoic acid can directly induce the expression of gut-homing molecules on proliferating T cells, a process strongly enhanced by bone marrow-derived dendritic cells in vitro. Therefore, cooperation of sessile lymph node stromal cells with mobile dendritic cells warrants the imprinting of tissue specific homing receptors on activated T cells.

Better preservation of the peritoneum in rats exposed to amino acid-based peritoneal dialysis fluid.

BACKGROUND: Glucose-containing peritoneal dialysis fluids (PDF) show impaired biocompatibility, which is related partly to their high glucose content, presence of glucose degradation products, low pH, and lactate buffer, or a combination of these factors. In a rat chronic peritoneal exposure model, we compared effects of an amino acid-based PDF (AA-PDF) with a glucose-containing PDF on the peritoneal microcirculation and morphology. METHOD: Two groups of rats received 10 mL of either fluid daily for 5 weeks via peritoneal catheters connected to implanted subcutaneous mini vascular access ports. Leukocyte-endothelium interactions in the mesenteric venules were investigated by intravital microscopy. Quantification of angiogenesis and fibrosis and inspection of the mesothelial cell layer were performed by light and electron microscopy. RESULTS: Daily exposure to glucose-containing PDF resulted in a significant increase in the number of rolling leukocytes in mesenteric venules, whereas instillation of AA-PDF did not change the level of leukocyte rolling. Glucose-containing PDF evoked a significantly higher number of milky spots in the omentum, whereas this response was significantly reduced in animals exposed to the AA-PDF (p < 0.02). Chronic instillation of glucose-containing PDF induced angiogenesis in various peritoneal tissues, accompanied by fibrosis in the mesentery and parietal peritoneum. Quantitative morphometric evaluation of omentum and mesentery showed a clear trend toward less angiogenesis after treatment with the AA-PDF compared to the glucose-containing PDF, which reached statistical significance in the parietal peritoneum (p < 0.04). Instillation of AA-PDF resulted in approximately 50% reduction of fibrosis in the mesentery (p < 0.04) and approximately 25% reduction in the parietal peritoneum (p < 0.009) compared to glucose-containing PDF. Glucose-containing PDF damaged the mesothelial cell layer, whereas the mesotheium was intact after AA-PDF treatment, as evidenced by electron microscopy. CONCLUSION: Our data in a rat chronic peritoneal exposure model clearly demonstrate reduced immune activation (evidenced by decreased number of rolling leukocytes and decreased induction of omental milky spots) and reduced neoangiogenesis, fibrosis, and mesothelial damage of the peritoneal membrane after treatment with AA-PDF compared to glucose-containing PDF.

Immunopathological changes in a uraemic rat model for peritoneal dialysis.

BACKGROUND: Peritoneal dialysis (PD) is a treatment modality for patients with renal failure. Both the uraemic state of these patients and chronic exposure to PD fluid are associated with the development of functional and structural alterations of the peritoneal membrane. In a well-established chronic PD rat model, we compared rats with normal renal function with subtotal nephrectomized rats that developed uraemia. METHODS: Uraemic and control rats received daily 10 ml conventional glucose containing PD fluid, via peritoneal catheters during a 6 week period. Uraemic and control rats receiving no PD fluid served as controls. Parameters relevant for peritoneal defence and serosal healing responses were analyzed. RESULTS: Uraemic animals were characterized by 2-3-fold increased serum urea and creatinine levels, accompanied by a significantly reduced haematocrit. Uraemia (without PD fluid exposure) induced new blood vessels in different peritoneal tissues, accompanied by increased accumulation of advanced glycation end products (AGEs) and elevated levels of angiogenic factors such as vascular endothelial growth factor and monocyte chemoattractant protein-1 (MCP-1) in peritoneal lavage fluid. A much stronger peritoneal response was observed upon PD fluid exposure in non-uraemic rats. This included the induction of angiogenesis and fibrosis in various peritoneal tissues, accumulation of AGEs, immunological activation of the omentum, damage to the mesothelial cell layer, focal formation of granulation tissues and increased MCP-1 and hyaluronan levels in peritoneal lavage fluid. Finally, chronic PD fluid instillation in uraemic rats did not induce an additional peritoneal response compared to PD fluid exposure in non-uraemic rats, except for the degree of AGE accumulation. CONCLUSIONS: Both uraemia and PD fluid exposure result in pathological alterations of the peritoneum. However, uraemia did not induce major additive effects to PD fluid-induced injury. These results substantially contribute to the understanding of the pathobiology of the peritoneum under PD conditions.

Beneficial effects of aminoguanidine on peritoneal microcirculation and tissue remodelling in a rat model of PD.

BACKGROUND: The formation of glucose degradation products (GDPs) and accumulation of advanced glycation end products (AGEs) partly contribute to the bioincompatibility of peritoneal dialysis fluids (PDF). Aminoguanidine (AG) scavenges GDPs and prevents the formation of AGEs. METHODS: In a peritoneal dialysis (PD) rat model, we evaluated the effects of the addition of AG to the PDF on microcirculation and morphology of the peritoneum, by intravital microscopy and quantitative morphometric analysis. RESULTS: AG-bicarbonate effectively scavenged different GDPs from PDF. Daily exposure to PDF for 5 weeks resulted in a significant increase in leucocyte rolling in mesenteric venules, which could be reduced for approximately 50% by addition of AG-bicarbonate (P<0.02). Vascular leakage was found in rats treated with PDF/AG-bicarbonate, but not with PDF alone. Evaluation of visceral and parietal peritoneum showed the induction of angiogenesis and fibrosis after PDF instillation. PDF/AG-bicarbonate significantly reduced vessel density in omentum and parietal peritoneum (P<0.04), but not in mesentery. PDF-induced fibrosis was significantly reduced by AG (P<0.02). PDF instillation led to AGE accumulation in mesentery, which was inhibited by supplementation of AG. Since addition of AG-bicarbonate to PDF raised pH from 5.2 to 8.5, a similar experiment was performed with AG-hydrochloride that did not change the fluid acidity. We could reproduce most of the results obtained with AG-bicarbonate; however, AG-hydrochloride induced no microvascular leakage and had a minor effect on angiogenesis. CONCLUSION: The supplementation of either AG reduced a number of PDF-induced alterations in our model, emphasizing the involvement of GDPs and/or AGEs in the PDF-induced peritoneal injury.

Contribution of lactate buffer, glucose and glucose degradation products to peritoneal injury in vivo.

BACKGROUND: Long-term peritoneal dialysis (PD) is associated with the development of functional and structural alterations of the peritoneal membrane. In this study, we investigated the contribution of low pH lactate buffer, high glucose concentration and glucose degradation products to peritoneal injury in a rat peritoneal exposure model. METHODS: Rats received daily 10 ml of either heat-sterilized (3.86% glucose, pH 5.2, n = 8) or filter-sterilized PD fluid (3.86% glucose, pH 5.2, n = 8), or lactate buffer (pH 5.2, n = 8) via a mini vascular access port during a 10 week period. Untreated rats served as controls. RESULTS: The low pH lactate buffer instillation induced pronounced morphological changes including the induction of angiogenesis in various peritoneal tissues and mild damage to the mesothelial cell layer covering the peritoneum. It also evoked a cellular response characterized by an increased mesothelial cell density on the liver, the induction of milky spots and accumulation of omental mast cells in the omentum, and significant changes in the composition of peritoneal leukocytes. The addition of glucose to low pH lactate buffer (filter-sterilized PD fluid) strengthened most, but not all of the responses described above and induced a fibrogenic response. In addition to glucose and low pH lactate buffer, the presence of glucose degradation products (heat-sterilized PD fluid) significantly induced an additional omental milky spot response (P < 0.03) and caused profound mesothelial damage. The vessel density in the omentum and the mesentery was significantly correlated to both the number of tissue mast cells and the hyaluronan content in the peritoneal lavage, which might suggest a role for mast cells and hyaluronan in the induction of angiogenesis. CONCLUSIONS: Instillations of low pH lactate buffer, a high glucose concentration and glucose degradation products contribute differently and often cumulatively to peritoneal injury in vivo.

Better preservation of peritoneal morphologic features and defense in rats after long-term exposure to a bicarbonate/lactate-buffered solution.

The long-term effects of a standard lactate-buffered dialysis fluid and a new, two-chamber, bicarbonate/lactate-buffered dialysis fluid (with fewer glucose degradation products and a neutral pH) were compared in an in vivo peritoneal exposure model. Rats were given daily injections, via an access port, of 10 ml of standard solution or bicarbonate/lactate-buffered solution for 9 to 10 wk. The omentum, peritoneum, and mesothelial cell layer were screened for morphologic changes. In addition, the bacterial clearing capacity of the peritoneal cells was studied. Significantly more milky spots and blood vessels were observed in the omenta of animals treated with standard solution (P < 0.03 for both parameters). Electron-microscopic analysis demonstrated dramatic changes in the appearance of the vascular endothelial cells of the milky spots and a severely damaged or even absent mesothelium on the peritoneal membrane of the standard solution-treated animals. In contrast, the mesothelium was still present in the bicarbonate/lactate-buffered solution group, although the cells lost microvilli. Both peritoneal dialysis fluids significantly increased the density of mesothelial cells (per square millimeter) on the surface of the liver and the thickness of the submesothelial extracellular matrix of the peritoneum (both P < 0.04 for both fluids versus control). A significantly better ex vivo bacterial clearing capacity was observed with peritoneal cells from the bicarbonate/lactate-buffered solution group, compared with the standard solution group (P < 0.05 in both experiments). These results demonstrate that instillation of bicarbonate/lactate-buffered solution into rats for 9 to 10 wk preserves both morphologic and immune parameters much more effectively, compared with standard solution. These findings may be of considerable clinical importance.