Role of T lymphocytes in intestinal mucosal injury. Inflammatory changes in athymic nude rats

Villus epithelial injury induced by infection with the nematode Nippostrongylus brasiliensis is associated with upregulation of granzyme B

Intestinal parasite infections induce thymus-dependent villus atrophy, but the effector mechanisms directly responsible for the development of villus atrophy are not thoroughly understood. In this study, we analyzed the expression of cytotoxic factors or ligands in athymic nude rnu/rnu rats and their littermate euthymic rnu/+ rats infected with the nematode Nippostrongylus brasiliensis. Morphometric analyses showed that partial villus atrophy developed 10 days after infection in euthymic but not in athymic rats, whereas crypt hyperplasia occurred in both types of animal. Reverse transcription-polymerase chain reaction analyses of the isolated jejunal epithelial fraction showed that the development of villus atrophy in euthymic rats was positively correlated with an increase of granzyme B transcript levels but not with Fas ligand or tumor necrosis factor-alpha expression. In addition, the number of granzyme B-immunoreactive cells was increased significantly in euthymic rat villus epithelium and the propria mucosa after infection. The CD8+ cell number did not change significantly. Collectively, these findings showed that significant increases in the number of cells that express the cytotoxic factor granzyme B occur in the nematode-infected small intestine of immunocompetent hosts. The type of cells that express granzyme B and their role in the progression of enteropathy remain to be elucidated.

Experimental enteropathy in athymic and euthymic rats: synergistic role of lipopolysaccharide and indomethacin

The aim of this study was to investigate the immunologic and microbiological bases of indomethacin enteropathy. Athymic nude and euthymic specific pathogen-free (SPF) rats were reared under conventional or SPF conditions. In each group, indomethacin was given intrarectally for 2 days. Indomethacin enteropathy was evaluated using a previously described ulcer index and tissue myeloperoxidase activity. Both euthymic and athymic nude rats developed intestinal ulcers to the same degree under conventional conditions but no or minimal ulcer under SPF conditions. Pretreatment of conventional rats with intragastric kanamycin sulfate, an aminoglycoside antibiotic, attenuated indomethacin enteropathy in a dose-dependent fashion. Interestingly, when lipopolysaccharide was injected intraperitoneally in kanamycin-pretreated rats, it fully restored enteropathy in these rats in a dose-dependent manner. We confirmed that kanamycin decreased the number of gram-negative bacteria and endotoxin concentration of the small intestine in a dose-dependent fashion. These results indicate that indomethacin enteropathy is bacteria dependent and does not require a T cell function. Synergy between indomethacin and bacterial lipopolysaccharide may play a major role in this enteropathy.

Review article: In vitro models in inflammatory bowel disease research--a critical review

Research efforts in inflammatory bowel disease (IBD) have been directed towards the epithelium as it has become clear that epithelial cells play a critical role in inflammatory response. Most research involving IBD employs in vitro techniques. In vitro epithelial cell studies have played and are continuing to play a major role in providing specific information relevant to IBD. Thus, such studies have provided irrefutable evidence that epithelial responses can be induced by microbes/microbial products and by immune activation. Culture experiments have provided insights into the effects of individual cytokines and other inflammatory mediators on epithelial pathophysiology, injury and repair, apoptosis, necrosis, and other processes that may be involved in IBD. Activated epithelial cells can participate in and even orchestrate immune responses, by stimulating T cells (and possibly others) and by producing cytokines that recruit specific inflammatory cells. Physiological regulation of epithelial tight junctions has been demonstrated by in vitro studies; the implication of this information for treating IBD is just beginning to be explored. It is becoming increasingly clear that epithelial processing and presentation of antigens is critical to the outcome of the immune response.

Feeding heated soyabean flour increases the density of B and T lymphocytes in the small intestine of calves

The effect of dietary antigens on the gut morphology and density of immune cells was studied in preruminant calves fed milk substitutes containing skim milk powder (SMP), non-antigenic hydrolysed soya protein isolate (HSPI) or antigenic heated soyabean flour (HSF) as their main protein source for 3 months. The height and perimeter of proximal jejunum villi were highest in the calves fed SMP and lowest in those fed HSF (P < 0.05). In contrast, the crypt depth and perimeter were apparently not influenced by the dietary treatments studied. This morphological alteration was associated with a dramatic infiltration of the lamina propria by B and T lymphocytes in the calves fed HSF (P < 0.01). Increased B cell density was essentially accounted for by IgA-, IgG1- and IgG2-bearing cells. The density of CD2-positive T lymphocytes increased (P < 0.01) in the jejunal lamina propria of HSF calves, involving helper (CD4+) and suppressor-cytotoxic (CD8+) T cell subsets. The density of gamma-delta (WC1+) T cells also increased (P < 0.01). The major change concomitantly observed in the villus epithelium was an increased density of CD8+ cells (P < 0.05) and WC1 + cells (P < 0.01).

T cell-monocyte interactions regulate epithelial physiology in a coculture model of inflammation

We have examined the effect of T cell activation, with or without monocytes, on epithelial electrolyte transport and barrier functions. Confluent monolayers of human T84 epithelial cells were cocultured (1-3 days) with peripheral blood mononuclear cells (PBM) or T cells activated by anti-CD3 antibody. Monolayers were then mounted in Ussing chambers, and changes in ion transport (indicated by short-circuit current, Isc) and barrier (indicated by resistance and radiolabeled probe fluxes) functions were assessed. Coculture with activated PBM or conditioned medium from these cells altered the transport (decreased Isc responses to carbachol and forskolin) and barrier (decreased resistance and increased fluxes of [3H]mannitol and 51Cr-EDTA) properties of T84 monolayers. In contrast, coculture with equal numbers of T cells activated in the absence of monocytes did not significantly affect epithelial physiology. Monocytes treated with conditioned media from activated T cells evoked epithelial abnormalities similar to those caused by culture with activated PBM. Total correction of epithelial abnormalities was achieved only by treating T cell-conditioned medium with anti-interferon-gamma (IFN-gamma) before addition to monocytes, as well as addition of anti-tumor necrosis factor-alpha (TNF-alpha) to the coculture. Exogenous recombinant IFN-gamma and TNF-alpha added to T84 monolayers did not mimic the physiological changes induced by immune cells; addition of these cytokines to monocytes did reproduce the effects. We conclude that T cell-derived IFN-gamma activates monocytes to release TNF-alpha and other soluble mediators, resulting in epithelial dysfunction.

Functional and morphological changes in small bowel of Crohn's disease patients. Influence of site of disease

Morphological and functional changes were examined in the upper jejunum and terminal ileum of 18 patients suffering from Crohn's disease. Intestinal permeability, biochemical determination of enzymatic activities, and morphologic evaluation of the severity of the lesions were evaluated. Ulcerative colitis and irritable bowel syndrome patients served as controls. We found abnormal lactulose-mannitol tests in all patients with active Crohn's disease. Permeability changes correlated with increased crypt cell proliferation, as indicated by thymidine kinase activity. A significant reduction in brush border enzyme activities was seen in the terminal ileum, but no significant change was observed in the unaffected upper jejunum. The number of mast cells was increased in the diseased ileum. We conclude that the site of inflammation and the healing capacity of the epithelium are important in determining functional and biochemical abnormalities in active Crohn's disease. Changes may be dependent on the type and number of immune cells involved in the inflammatory process.

Role of T lymphocytes in secretory response to an enteric nematode parasite. Studies in athymic rats

Athymic (nude) rats have been used to assess the role of thymus-dependent T cells in the control of the intestinal response following infection with the enteric parasite, Nippostrongylus brasiliensis. Tissues from infected rats were excised on days 4, 7, 10, and 21 postinfection (p-i) for physiological and morphological studies; uninfected (day 0) rats served as controls. In response to the worm burden, jejunal tissues displayed a secretory response, indicated by an elevated baseline short-circuit current (Isc) on days 7 and 10 p-i, and were more responsive to histamine than control tissues. Despite this enhanced secretory response, approximately 35% of the worm burden was still present on day 21 p-i (compared with expulsion of > 95% by day 14 p-i in normal rats). Mast cell activation and hyperplasia, increased goblet cell (implying increased mucus synthesis) and intraepithelial leukocyte numbers, and abnormalities in Isc responses after electrical stimulation of enteric nerves were identified following infection. These events in nude rats were attenuated or delayed in onset as compared with conventional immunocompetent rats. Our results support the postulate that thymus-dependent T cells regulate the timing and/or nature of the mucosal response to enteric parasitic infections. However, ion secretion was not altered in the absence of T cells and, therefore, is more likely to be a consequence of mast cell activation.

Phenotypic and functional characterization of T-cell lines generated from colonoscopic biopsy specimens in patients with ulcerative colitis

Intestinal T-cell lines were generated from lamina propria mononuclear cells isolated from colonoscopic biopsies in ulcerative colitis patients and controls. In both ulcerative colitis and controls, expanded cells were constituted largely by T-cell receptor alpha beta+, CD4+, CD45RA- (helper), and CD8+, CD11b- (cytotoxic) phenotypes. T-cell receptor V beta gene usage was not significantly changed after cell expansion and no difference was observed between ulcerative colitis and controls. Ulcerative colitis cells, especially those derived from the patients with long-standing disease, showed significantly higher levels of cytotoxicity against the target cells, including those of colonic epithelial origin, and enhanced production of tumor necrosis factor-alpha and interferon-gamma after short incubation with anti-CD3 antibody. Generation of T-cell lines from colonoscopic biopsy specimens may be useful for detailed functional characterization of locally infiltrating T cells in ulcerative colitis patients.

Genetic mapping of the athymic nude (RNU) locus in the rat to a region on chromosome 10

The nude trait in the rat is transmitted in an autosomal recessive manner and is associated with thymic aplasia, T-cell deficiency, and hairlessness. Congenic rats homozygous for the RNU (Rowett nude) locus are important models in the study of inflammatory disease, tumor growth, and transplant rejection. The RNU locus has not been previously mapped, and the nature of the gene product is unknown. To determine the map location of this gene, a single F344.rnu/rnu (athymic nude congenic Fischer rat) male congenic rat was bred with 3 LEW/N (NIH stock Lewis rat) female rats to produce F1 progeny. Twelve F1 brother-sister breeding pairs were established. Forty-nine phenotypically nude F2 offspring (198 total) were obtained. Linkage analysis done on F2 DNA revealed highly significant cosegregation between the nude phenotype and eight polymorphic markers located on Chromosome (Chr) 10. The tightest linkages were with: MYH3 (embryonic, skeletal myosin heavy chain) and SHBG (sex hormone-binding globulin), giving 2 point lod scores of 20.2, and 20.0, respectively. The map order and map distances, determined by multipoint linkage calculations, were: RR24-(16.1 cM)-MYH3-(3.5 cM)-SHBG-(4.7 cM)-RNU-(11.9 cM)-F16F2-(24.1 cM)-CLATP (citrate lyase ATPase)-(2.4 cM)-ACE (angiotensin converting enzyme)/PPY (pancreatic polypeptide)-(14.1 cM)-RR1023. The position of the RNU locus in the rat corresponds closely with that of the recently reported nu locus in the mouse. This finding suggests that the nude phenotype in the rat and the mouse arise from defects in homologous genes.