Hypersensitivity reactions in the small intestine. 2. Effects of allograft rejection on mucosal architecture and lymphoid cell infiltrate

Human intraepithelial lymphocytes

The location of intraepithelial lymphocytes (IEL) between epithelial cells, their effector memory, cytolytic and inflammatory phenotype positions them to kill infected epithelial cells and protect the intestine against pathogens. Human TCRαβ+CD8αβ+ IEL have the dual capacity to recognize modified self via natural killer (NK) receptors (autoreactivity) as well as foreign antigen via the T cell receptor (TCR), which is accomplished in mouse by two cell subsets, the naturally occurring TCRαβ+CD8αα+ and adaptively induced TCRαβ+CD8αβ+ IEL subsets, respectively. The private/oligoclonal nature of the TCR repertoire of both human and mouse IEL suggests local environmental factors dictate the specificity of IEL responses. The line between sensing of foreign antigens and autoreactivity is blurred for IEL in celiac disease, where recognition of stress ligands by induced activating NK receptors in conjunction with inflammatory signals such as IL-15 can result in low-affinity TCR/non-cognate antigen and NK receptor/stress ligand interactions triggering destruction of intestinal epithelial cells.

Food intolerance and mucosal inflammation

Most infants are immunologically active and are able to develop a tolerance to oligoclonal antigens by producing IgA, along with activation of regulatory T cells, in early infancy. Cytokines and their signaling molecules are important mediators in the intestine, regulating both oral tolerance and mucosal inflammation. This system works efficiently in most individuals, but for an as yet undefined reason, some people react to food and other proteins as though they were pathogens, with induction of chronic inflammation in the mucosa. The adverse reaction caused by ingested foods is defined as food intolerance. The clinical features of food intolerance include vomiting, diarrhea, bloody stool, eczema, failure to thrive, and a protean range of other symptoms. Intolerance can be divided into two categories depending on whether or not they are immunologically mediated. Food intolerance and mucosal inflammation are deeply related because tolerance cannot be established when there is an inflammation in the intestinal mucosa. Mast cells, eosinophils, mucosal lymphocytes, and epithelial cells are deeply involved and related to each other in the development of mucosal inflammation. Meanwhile, rectal bleeding in infancy is related to lymphoid hyperplasia with eosinophil infiltration into the colonic mucosa facilitated by C-C motif ligand 11 (CCL11, known as eotaxin-1) and C-X-C motif chemokine ligand 13 (CXCL13). Rectal bleeding in infancy may not be simply caused by allergic reactions against specific antigens, but may be due to migrated lymphocytes developing immunological tolerance; including IgA synthesizing, in the intestinal mucosa.

High dose multiple micronutrient supplementation improves villous morphology in environmental enteropathy without HIV enteropathy: results from a double-blind randomised placebo controlled trial in Zambian adults

BACKGROUND

Environmental enteropathy (EE) is an asymptomatic abnormality of small bowel structure and function, which may underlie vaccine inefficacy in the developing world. HIV infection co-exists in many of these populations. There is currently no effective treatment. We conducted a secondary analysis of a randomised controlled trial of high dose multiple micronutrient (MM) supplementation on small bowel architecture in EE in participants with or without HIV infection.

METHODS

In a double-blind parallel-group trial of the effect of MM on innate immune responses to oral vaccines, consenting Zambian adults were randomised to receive 6 weeks of 24 micronutrients as a daily capsule or placebo. HIV status was established after randomisation. Proximal jejunal biopsies were obtained after the supplementation period. Villous height, crypt depth, villous width, villous perimeter per 100 μm muscularis mucosa (a measure of epithelial surface area), and villous cross sectional area per 100 μm muscularis mucosa (a measure of villous compartment volume) were measured in orientated biopsy sections using semi-automated image analysis. Analysis was by intention to treat.

RESULTS

18 patients received MM and 20 placebo. 6/18 MM and 9/20 placebo patients had HIV. In HIV negative patients given MM compared to placebo, mean villous height was 24.0% greater (293.3 v. 236.6 μm; 95% CI of difference 17.7-95.9 μm; P = 0.006), mean villous area was 27.6% greater (27623 v. 21650 μm2/100 μm; 95% CI of difference 818-11130 μm2/100 μm; P = 0.03), and median villous perimeter was 29.7% greater (355.0 v. 273.7 μm/100 μm; 95% CI of difference 16.3-146.2 μm/100 μm; P = 0.003). There was no significant effect on crypt depth or villous width. No effect was observed in HIV positive patients. There were no adverse events attributable to MM.

CONCLUSIONS

MM improved small bowel villous height and absorptive area, but not crypt depth, in adults with EE without HIV. Nutritional intervention may therefore selectively influence villous compartment remodelling. In this small study, there was a clear difference in response depending on HIV status, suggesting that EE with superimposed HIV enteropathy may be a distinct pathophysiological condition.

Pathophysiology of celiac disease

Celiac disease results from the interplay of genetic, environmental, and immunologic factors. An understanding of the pathophysiology of celiac disease, in which the trigger (wheat, rye, and barley) is known, will undoubtedly reveal basic mechanisms that underlie other autoimmune diseases (eg, type 1 diabetes) that share many common pathogenic perturbations. This review describes seminal findings in each of the 3 domains of the pathogenesis of celiac disease, namely genetics, environmental triggers, and immune dysregulation, with a focus on newer areas of investigation such as non-HLA genetic variants, the intestinal microbiome, and the role of the innate immune system.

Integration of genetic and immunological insights into a model of celiac disease pathogenesis

Celiac disease (CD) is a gluten-sensitive enteropathy that develops in genetically susceptible individuals by exposure to cereal gluten proteins. This review integrates insights from immunological studies with results of recent genetic genome-wide association studies into a disease model. Genetic data, among others, suggest that viral infections are implicated and that natural killer effector pathways are important in the pathogenesis of CD, but most prominently these data converge with existing immunological findings that CD is primarily a T cell-mediated immune disorder in which CD4(+) T cells that recognize gluten peptides in the context of major histocompatibility class II molecules play a central role. Comparison of genetic pathways as well as genetic susceptibility loci between CD and other autoimmune and inflammatory disorders reveals that CD bears stronger resemblance to T cell-mediated organ-specific autoimmune than to inflammatory diseases. Finally, we present evidence suggesting that the high prevalence of CD in modern societies may be the by-product of past selection for increased immune responses to combat infections in populations in which agriculture and cereals were introduced early on in the post-Neolithic period.

Chronic allergy to dietary ovalbumin induces lymphocyte migration to rat small intestinal mucosa that is inhibited by MAdCAM-1

Few models have described a chronic food allergy with morphological changes in the intestinal mucosa. Here we established an ovalbumin (OVA)-induced, cell-mediated, allergic rat model and examined lymphocyte migration in the gut. Brown Norway rats were intraperitoneally sensitized to OVA and then given 10 mg OVA/day by gastric intubation for 6 wk. Lymphocyte subsets and adhesion molecules were examined immunohistochemically, and the migration of T lymphocytes to microvessels of Peyer's patches and villus mucosa was observed by using an intravital microscope. Serum OVA-specific IgG and IgE levels were increased in animals repeatedly exposed to OVA. Significant villus atrophy and increased crypt depth was accompanied by increased infiltration of T lymphocytes in the small intestinal mucosa of the group given OVA. Expression of rat mast cell protease II and of mucosal addressin cell adhesion molecule-1 (MAdCAM-1) was also increased in these groups. The administration of anti-MAdCAM-1 antibody significantly attenuated the OVA-induced changes in the mucosal architecture and in CD4 T lymphocyte infiltration. Intravital observation demonstrated that in rats with a chronic allergy, T lymphocytes significantly accumulated in villus microvessels as well as in Peyer's patches via a MAdCAM-1-dependent process. Our model of chronic food allergy revealed that lymphocyte migration was increased with MAdCAM-1 upregulation.

Impaired rejection and mucosal injury of small intestinal allografts lacking the interferon-gamma receptor

Small intestinal mucosal T cell activation results in villous atrophy and crypt hyperplasia. There is conflicting evidence as to whether a Th1 IFN-gamma response may be involved. Using a murine intestinal transplant model of T cell-mediated enteropathy we aimed to study the role of IFN-gamma on the development of villous atrophy and crypt hyperplasia. Isografts or allografts of foetal small intestine from 129SV-/- IFN-gamma receptor knockout mice or wild type mice were implanted under the kidney capsule of Balb/c recipient mice. Grafts were examined histologically at intervals from 2 to 9 days post implantation for signs of rejection. Quantitative rtPCR for IFN-gamma, TNFalpha and IL-4 was conducted on grafts at 5 and 9 days post implantation. In allografts, rejection accompanied by the development of villous atrophy and crypt hyperplasia, occurred in a time-dependent manner. However this process was markedly slower in the IFN-gamma receptor knockout grafts compared to the wild type grafts at 5 days (chi2 = 10.08, P = 0.007) and 9 days post implantation (chi2 = 13.25, P = 0.004). There were also significantly fewer TNFalpha transcripts in allografts of IFN-gamma-/- intestine than in wild type allografts (P = 0.02). IFN-gamma has a partial, but not obligatory, role in the development of villous atrophy and crypt hyperplasia during T cell mediated rejection of intestinal allografts.

Regulation of mucosal immune responses in effector sites

In human disease and rodent models, immune responses in the intestinal mucosa can be damaging. Damage is characterised by villus atrophy, crypt hyperplasia and reduced ability to digest and absorb nutrients. In normal individuals active responses to harmless environmental antigens associated with food and commensal bacteria are controlled by the development of immunological tolerance. Similar pathological changes occur in piglets weaned early from their mothers. Active immune responses to food antigens are observed in these piglets, and we and others have hypothesised that the changes occur as a result of transient allergic immune responses to novel food or bacteria antigens. The normal mechanism for producing tolerance to food antigens may operate at induction (Peyer's patches and mesenteric lymph nodes) or at the effector stage (intestinal lamina propria). In our piglet studies immunological tolerance occurs despite the initial active response. Together with evidence from rodents, this observation suggests that active responses are likely to be controlled at the effector stage, within the intestinal lamina propria. Support for this mechanism comes from the observation that human and pig intestinal T-cells are susceptible to apoptosis, and that this process is accelerated by antigen. We suggest that the role of the normal mature intestinal lamina propria is a balance between immunological effector and regulatory function. In neonatal animals this balance develops slowly and is dependant on contact with antigen. Immunological insults such as weaning may tip the balance of the developing mucosal immune system into excessive effector or regulatory function resulting in transient or chronic allergy or disease susceptibility.

Transforming growth factor-beta: an important cytokine in the mucosal immune response

Cytokines are important mediators in the intestine regulating both oral tolerance and mucosal inflammation. Central to this immune-regulatory role is the cytokine transforming growth factor-beta (TGF-beta). Oral tolerance and inflammatory responses in the gut are regulated through the balance of the Th1, Th2, and Th3 lymphocyte responses--a balance influenced strongly by TGF-beta. TGF-beta also modulates B-cell responses by increasing the production of immunoglobulin A (IgA) while decreasing the production of IgG, IgM, and IgE. In intestinal epithelial cells, TGF-beta activates signal transduction pathways resulting in the inhibition of proliferation and tumorigenesis. Currently, these signaling pathways are being dissected at the molecular level.

Chronic oral antigen exposure induces lymphocyte migration in anaphylactic mouse intestine

Persistent diarrhea, vomiting, and dehydration are symptoms often seen in patients suffering from food allergy after chronic antigen exposure; however, the precise mechanisms involved have not been well defined. In an effort to clarify the mechanisms of the chronic intestinal changes attributable to genuine IgE-mediated anaphylactic reactions induced by orally administered antigen, a mouse model was established by s.c. implantation of a murine hybridoma capable of producing monoclonal anti-trinitrophenyl IgE antibody, and the morphologic and immunologic changes occurring in the intestine upon chronic antigen exposure were investigated. In the early stage after ingestion of the antigen, diarrhea and noticeable infiltration of mast cells as well as eosinophils into the lamina propria were observed. A substantial increase in serum histamine levels as well as an increase in leukotriene C4 synthesis in the jejunal mucosa were observed 1 h after antigen challenge. Also, the synthesis of leukotriene B4 was significantly elevated for up to 9 h after antigen challenge. The expression of both intercellular adhesion molecule-1 (ICAM-1) on mucosal vascular endothelial cells and IAd on epithelial cells was markedly enhanced, and noticeable infiltration of eosinophils and lymphocytes was also confirmed in the mouse model after chronic antigen exposure. These findings suggest that oral antigen exposure induces anaphylactic reactions in the intestine mediated by mast cells and eosinophils in response to the IgE-antigen complex in the early phase, and also induces lymphocyte migration after chronic antigen exposure.

Small bowel transplantation in children: an immunohistochemical study of intestinal grafts

Seven children with short bowel syndrome underwent small bowel allografting. Episodes of early rejection were observed in five patients who received a graft from paediatric or adult donors but not in two patients who received a neonatal graft. This study aimed, firstly, to define immunohistochemical parameters accompanying rejection and, secondly, to compare immunohistochemical parameters in neonatal grafts with those in grafts from older donors. An immunohistochemical analysis was performed on 85 intestinal biopsy specimens taken for monitoring the transplant. Acute histological rejection was associated with pericryptic infiltrates of CD3+TcR alpha beta + T cells containing clusters of CD8+ cells, numerous CD25+ cells, and increased numbers of CD68+ macrophages. These changes were associated with the appearance of major histocompatibility (MHC) class II antigens on crypt enterocytes and with an appreciable increase in the expression of E-selectin on mucosal endothelial cells. Immunohistochemistry was useful in predicting rejection by showing the appearance of pericryptic CD25+ T cells 48 hours before the first histological lesions of crypt necrosis. Comparison of neonatal grafts with grafts from older donors did not show any significant difference in the density of CD68+ macrophages or in the endothelial expression of intercellular adhesion molecule-1, vascular cell adhesion molecule-1, or E-selectin. In contrast to grafts from older donors, however, neonatal grafts did not express MHC class II antigens on epithelial cells and contained very low numbers of intraepithelial lymphocytes. These data indicate, firstly, that immunohistochemistry is useful for monitoring intestinal transplants and, secondly, that the better clinical tolerance of neonatal allografts may be related to the lower immunogenicity of the neonatal epithelium.

T-cell responses and cellular immunity in coeliac disease

Increasing evidence points to a direct role for T cells in the mediation of the coeliac intestinal lesion. There is good evidence for increased local T-cell reactivity, manifest as increased in T-cell activation in the lamina propria and T-cell proliferation in the epithelial compartment. A likely scenario is that gluten elicits antigen-specific responses by lamina propria T helper cells, probably of the Th1 (inflammatory-mediator) subtype, leading to secretion of pro-inflammatory cytokines. Such cytokines may have direct effects on intestinal enterocytes, as well as mediating indirect effects by upregulation of MHC antigens and by enhancing the activity of cytolytic T cells. Although gluten-specific IEL responses have not been demonstrated by intraepithelial T lymphocytes (IELs), increasing evidence suggests that IELs can act as cytolytic effector cells and hence are likely to exert enteropathic effects under the influence of pro-inflammatory cytokines.

Coeliac disease research and clinical practice: maintaining momentum into the twenty-first century

Recent research shows that each word in the definition of coeliac disease, permanent gluten sensitive enteropathy, must now be reviewed, revised or reinterpreted. Permanent--but there are now well-documented cases of acquired disease, and perhaps also partial recovery of gut gluten tolerance. Enteropathy--gluten sensitivity is expressed in a spectrum, with a mild form seen as normal architecture with high count of intraepithelial lymphocytes. Gluten--the provoking agent--Investigators are intensively working to identify the precise toxic sequence, and to establish how this will link in with new genetic information. Mechanism of sensitivity? or hypersensitivity?--Critical to this is new knowledge on the modulation and regulation of immunity to intestinal antigens, including gliadin. A hypothesis is presented, as to the pathogenesis of gluten-sensitive enteropathy, which combines concepts of oral tolerance and of the regulation of expression of delayed type hypersensitivity reactions in the gut mucosa.

Dose-response studies of depletion and repopulation of rat intestinal mucosal mast cells after irradiation

The effects of radiation on gut mucosal mast cells (MMC) and tissue eosinophils were examined. Groups of rat were given single doses of whole-body irradiation from 0.5 to 5 Gy. Serum rat mast cell protease II (RMCPII) concentration showed a significant dose-dependent fall after 1 Gy on day 3 and 1.5 Gy on day 7. MMC counts and tissue RMCPII values on day 7 decreased significantly by 70% after 1 Gy and were undetectable with larger doses. Rat with normal and expanded MMC populations were irradiated or given anaphylaxis. Serum RMCPII concentrations did not change after irradiation, but there was a 10-fold increase in RMCPII after anaphylaxis. Tissue eosinophils in jejunum were 50% of control at 7 days after 2 Gy, and this effect was progressively more marked with higher doses. Similar effects on MMC and eosinophils were demonstrated in ileum, ascending colon and rectum. After 4.5 Gy, repopulation of the gut with MMC did not occur until week 3-4 postirradiation and MMC counts were still 50% below those of controls at 5 weeks postirradiation. Counts of tissue eosinophils 5 weeks after 4.5 Gy irradiation had returned to control levels in jejunum but were still significantly depleted in colon. These experiments show that the high radiosensitivity of rat intestinal MMC is dose dependent, similar at four different levels in the gastrointestinal tract and does not lead to immediate release of granule protease; repopulation with MMC does not begin until at 3 weeks postirradiation.

Celiac disease: clinical features and pathogenesis

Celiac disease is a fascinating illness, from both a clinical and research perspective. Most clinicians consider a diagnosis of celiac disease when a young patient has classic signs and symptoms of steatorrhea and severe malabsorption. However, the typical gastrointestinal symptoms often are absent. The patient may only have subtle signs of chronic malnutrition or nonspecific gastrointestinal complaints. Celiac disease is not diagnosed commonly in the United States, at least in part because of a low clinical index of suspicion. A diagnosis of celiac disease is confirmed by a small bowel mucosa biopsy. A dramatic clinical response to a gluten-free diet verifies the diagnosis, and provides a cost-effective treatment free of significant side effects. Strict adherence to the prescribed diet usually results in a complete resolution of the symptoms and mucosal histopathologic changes. The serious, long-term complication of intestinal lymphoma also may be prevented. To the clinical investigator, celiac disease is an important model of the HLA-associated immune-mediated illnesses. A specific HLA-DQ heterodimer is found in 95% of patients, representing perhaps the strongest association of any illness with a specific class II HLA molecule. In addition, an important environmental trigger (gluten) has been identified, providing a unique opportunity to study the interaction of gene products and environmental factors in the pathogenesis of an immune-mediated disease.

The interactive role of mucosal T lymphocytes in intestinal growth, development and enteropathy

Over the past 15-20 years, research has progressively focused on the mucosal T cell as the central factor in the initiation of physiological or pathological changes, first in the growth and maturation of the early (postnatal) intestine, and second in adult-type enteropathies resulting from sensitivity to either food or pathogen-derived antigens. T cell-mediated events may be measured, for example, in terms of specific immunopathologic patterns of change and injury, such as type 1 (lymphocyte infiltration), type 2 (crypt hyperplasia) and type 3 (flat-destructive), which can be recognized and quantitated microscopically; by determination of lymphocyte reactivity through secretion of interleukin-2 receptors (IL-2R) into plasma or expression by mucosal lymphocytes; by quantitation of lymphocyte subsets emigrating into inflamed tissues by immunoperoxidase-labelled monoclonal antibodies; or by the determination of T cell receptor polymorphisms. Alterations in intestinal growth, structure and function at weaning are likely to be T cell-mediated as they are analogous to the same type 1/2 lesions that reflect modulation of adult mucosal architecture in food and parasite-induced hypersensitivity reactions. Enteropathies associated with HIV infection and T cell deficiency display a milder degree of villous flattening and impaired crypt hyperplasia than that typical of gluten-sensitivity, suggesting a reversion to lesser degrees of mucosal pathology (type 1/2). Clearly more information will accrue; meanwhile the remarks in this brief survey should provide a firm basis whereby clinician and scientist can meet, and together recognize and further dissect the modulatory effect of T lymphocytes on mucosal structure and function.

The biology and pathobiology of the intestinal intraepithelial lymphocyte: a review of the literature

Intraepithelial lymphocytes represent a population of lymphocytes situated in the epithelial layer of all mucosae. In this report their biological and pathobiological features, with emphasis on intestinal intraepithelial lymphocytes, are reviewed.

The role of activated T lymphocytes in gastrointestinal disease

Activated T cells can be visualized in the intestinal lamina propria in a number of gastrointestinal diseases including food-sensitive enteropathy (coeliac disease), inflammatory bowel disease and intractable diarrhoea of infancy. Experimental studies have shown that T-cell activation in human intestinal lamina propria in vitro produces an increase in crypt cell proliferation, villous atrophy, increased HLA-DR expression on enterocytes, increased intra-epithelial lymphocyte numbers, and phenotypically, macrophage activation. All of these features are seen in human gastrointestinal disorders and it is proposed that T-cell activation to wheat (in coeliac disease), milk (cows' milk-sensitive enteropathy), and unidentified luminal antigens (Crohn's disease) plays a primary role in the pathogenesis of these disorders.

Changes in the rate of crypt epithelial cell proliferation and mucosal morphology induced by a T-cell-mediated response in human small intestine

The rate of crypt epithelial cell proliferation and mucosal morphology have been studied in vitro in explants of fetal human small intestine in organ culture in which a cell-mediated immune response has been elicited by stimulating lamina propria T cells with pokeweed mitogen or monoclonal anti-CD3 antibodies. Twelve hours after the addition of anti-CD3 or pokeweed mitogen, most lamina propria T cells expressed CD25. By 18 and 24 h after the addition of anti-CD3, there were significantly more crypt cells in the cell cycle than in controls, although villus height and crypt depth are the same in both groups. After 3 days, by dissecting microscopy, the villi appeared shorter in cultures in which the T cells were stimulated than in control cultures, and the mucosal surface was obscured by a layer of extruded enterocytes. Villus atrophy was confirmed by direct measurement of Feulgen-stained, microdissected villi. Crypts were longer in T-cell-stimulated cultures, and the rate of crypt epithelial cell proliferation measured by metaphase arrest was increased 10-fold. By electron microscopy, the microvilli and cellular morphology of the surface enterocytes were normal in T-cell-stimulated cultures. These experiments clearly show that a profound immune-mediated crypt epithelial cell hyperplasia can occur in the absence of damage to surface enterocytes.

Separate effects of irradiation and of graft-versus-host reaction on rat mucosal mast cells

T cell mediated immune responses in the gut can produce enteropathy and malabsorption. We have investigated the relevance of mucosal mast cells (MMC) to the mechanisms of this enteropathy by using graft-versus-host reaction (GvHR) in the rat as a model of mucosal delayed type hypersensitivity. Measurements of mucosal architecture, intraepithelial lymphocytes (IEL) and MMC counts were performed in control and experimental rats, and release of rat mast cell protease II (RMCPII) into the bloodstream was used as an index of MMC activation. In unirradiated rats, jejunal MMC count was increased on day 14 of the GvHR (mean 272/mm2 v 182 in controls, p less than 0.01), as was serum RMCPII (p less than 0.01). Irradiated rats (4.5 Gy, reconstituted with isogeneic spleen cells) had low counts of IEL and crypt hyperplasia seven to 14 days after irradiation. Irradiated rats with GvHR (induced by ip injection of parental strain spleen cells) and studied on days 7, 10 and 14, had significant enteropathy with longer crypts and higher CCPR than matched irradiated animals (p less than 0.05 on day 14 when compared with irradiation alone). Intraepithelial lymphocytes counts, however, reflected only the effect of radiation. Irradiation, with or without GvHR, led to the virtual disappearance of jejunal MMC, undetectable jejunal RMCPII and very low levels of RMCPII in serum (all p less than 0.01 when compared with unirradiated controls). These experiments show that there is a modest expansion in jejunal MMC in unirradiated rats with semiallogeneic GvHR, whereas irradiation, alone or associated with GvHR, profoundly depletes MMC for at least two weeks. The enteropathy of GvHR can evolve in the virtual absence of MMC.

Tumor-induced altered gastrointestinal steady-states: absence of MHC restriction in the paraneoplastic gastrointestine

The growth of a number of experimental rodent tumours including the Lewis lung tumour (LLca) progressively compromises the integrity of the host's gastroinestine by inducing cytokinetic alterations in the small bowel resembling those generally defining the intestinal phase of a graft-versus-host reaction (GVHR). To determine whether the induction of this paraneoplastic gastrointestine (PGI) involves, similar to a GVHR, a disparity between the MHC of the donor (LLca tumour) and the recipient (host), PGI development was evaluated in various LLca tumour-bearing murine strains that were either 'syngeneic' [C57BL/6 and BL/10 (H-2b)], 'semisyngeneic' [B6D2F1 (H-2bd) and B6C3F1 (H-2bk)] or 'allogeneic' [C3H/HeJ (H-2k) and DBA/2 (H-2d)] to the H-2b LLca tumour. The temporal appearance and magnitude of a PGI developing in either LLca-syngeneic or semi-syngeneic hosts, but not the allogeneic strains, suggested that the mechanism(s) involved in PGI development like the GVHR, was restricted by the MHC. Subsequent studies using congenic strains [B10.A (H-2k) and B10.D2/nSn (H-2d)], however, demonstrated that the mechanism(s) responsible for the PGI was restricted by the non-MHC loci of the C57BL mouse. These observations were supported by the appearance of a LLca-induced PGI in various B10.A congenic strains carrying mutations at the I-A or I-E/I-J loci of the MHC. Not unlike the intestinal phase of a GVHR, development of the PGI required the participation of enhanced mucosal mast cells which were limited in the WCB6F1 (S1/S1d) but not the (+/+) murine strains. These observations are discussed in light of the postulated premature migration of immature thymocytes that accompany tumour growth and their ability to non-specifically enhance (or suppress) cell mediated immune reactions in the host.

The immunopathology of the small intestinal reaction in gluten-sensitivity

Computerised image-analysis was used to define the spectrum of immunopathological changes in small intestinal mucosa in established celiac sprue disease; dermatitis herpetiformis; 1 degree relatives of celiac sprue patients, and treated celiac sprue patients challenged with varying doses of a peptic-tryptic digest of gluten. Typically, in flat ('Type 2') lesion there was a reduced number of large, mitotically active lymphocytes in surface epithelium, but an increased lymphocyte population in crypts. In approximately 50% untreated DH patients and in 20% 1 degree celiac sprue relatives, mucosal architecture was well-preserved although surface (villous) epithelium contained an expanded population of small, non-mitotic lymphocytes ('Type 1' lesion), with or without crypt hyperplasia. Similar changes were also induced by small dose gluten challenge. Larger dose challenges caused a progression from a Type 1 to a Type 2 lesion during a 5 day period of observation. In addition, observations on a few patients over 2-4 years showed a similar sequence of mucosal changes. A major feature of this sequence was the early appearance of crypt hypertrophy, before significant villous flattening had occurred. These changes parallel T lymphocyte-mediated graft- versus-host reactions in animals, suggesting that the specific immunopathologic features seen in gluten sensitivity are fundamentally cell-mediated in type, the degree of change probably dependent on host genetic factors. Finally, these data show that in becoming flat the mucosa must initially pass through the earlier Type 1 lesion in which crypt hypertrophy is a prominent response.

Evidence that activated mucosal T cells play a role in the pathogenesis of enteropathy in human small intestine

T cells in explants of human fetal small intestine in organ culture were stimulated in situ with PWM or anti-CD3 antibody to test the hypothesis that activated T cells produce enteropathy in human small intestine. T cell activation was measured by the appearance of CD25+ cells in the lamina propria of the explants and IL-2 production into the organ culture supernatant. We have previously shown that the number of T cells in human fetal gut increased between 14 and 22 wk gestation. Accordingly, after the addition of PWM to cultured explants of fetal intestine the number of CD25+ cells in the lamina propria and the amounts of IL-2 secreted into the organ culture supernatant increased with the age of the explanted tissue. The addition of PWM also produced an age-related enteropathy, most noticeably crypt epithelial cell hyperplasia and villous atrophy, with relatively minor changes in 14-17-wk-old intestine but severe tissue damage in 18-22-wk-old fetal intestine. These enteropathic effects were also produced when mucosal T cells were activated with anti-CD3 mAb. Cyclosporin A completely inhibited the PWM-induced development of CD25+ cells and related tissue damage. These experiments show that activated T cells in human small intestine produce enteropathy. The model provides a new system with which to dissect the mechanisms of T cell-mediated intestinal damage.

Frequency of occurrence and distribution of the intra-epithelial lymphoid cells in the follicle-associated epithelium in phenotypically normal and athymic nude mice

We have determined the number and pattern of spatial distribution of intraepithelial lymphoid cells in the follicle-associated epithelium of Peyer's patches and in the villus epithelium in the small intestine of athymic nu/nu mice and of the phenotypically normal mice kept in specified pathogen-free conditions. The results were obtained by histometric analysis of semithin histological sections. It has been found that the lymphoid cells were scattered randomly in the villus epithelium, while those in the follicle-associated epithelium were non-randomly distributed, occurring often in groups of several cells both for athymic nu/nu and phenotypically normal mice. The numbers of lymphoid cells in the follicle-associated and in the villus epithelium were found to be significantly lower in athymic nu/nu mice than in phenotypically normal mice kept in similar conditions. On the basis of the above results the proportions of thymus-dependent and thymus-independent lymphoid cells in the intestinal epithelium were deduced.

Morphological alterations of small intestinal epithelium of calves caused by feeding soybean protein

Sixteen male Holstein calves were fed milk replacer (14% solids) containing 23% crude protein from: 100% milk protein; or 66% soybean protein concentrate plus 34% milk protein as the only nutrients at 8, 9, 10, 11, 12, 12, and 12% body weight from 1 to 7 wk of age, respectively. Eight calves were sensitized to soybean by feeding 66% soybean protein concentrate plus 34% milk protein for 21 d and eight were not sensitized by feeding 100% milk protein. Afterward, each calf received one of the diets for 10 d followed by the other diet for an additional 10 d. During the 2nd wk of the initial period each calf was surgically fitted with a duodenal cannula for biopsy of intestinal mucosa. Biopsies were taken at surgery and on the last day of each period. Feeding 66% soybean protein concentrate plus 34% milk protein resulted in lower body weight gain, decreased feed efficiency, higher rectal temperatures, increased diarrhea, and villus atrophy. Diminished villi size supports other studies reporting allergic reaction to soybean protein and was associated with the poor performance observed in calves fed soybean protein.

Immune disorders of the gastrointestinal tract and liver

Immune disorders of the gastrointestinal tract and hepatobiliary systems comprise a diverse group of illnesses which share in common certain overlapping and yet distinctive expressions of cellular and humoral immunity. As is evident from material contained in this article, controversy and disparate results frequently characterize the study of immune mechanisms in a given disease process. Nonetheless, advances in quantitation of specific immunocyte function and phenotypic expression have greatly facilitated the depth of understanding of the immune process related to these disorders. Challenges for future clinical investigation of these disorders are to characterize cell-specific target antigens to which immunologic attack is directed and to unravel the immunogenetic mechanisms that trigger and direct immune-mediated injury to host tissues. It is anticipated that continued investigation of immune disorders of the gastrointestinal tract and liver will clarify pathogenetic mechanisms and thus permit formulation of rational and effective therapies.

Milk- and soy protein-induced enterocolitis: evidence for lymphocyte sensitization to specific food proteins

Stimulation ( [3H]thymidine incorporation) of blood lymphocytes cultured with food proteins was evaluated in infants with food protein-induced enterocolitis and correlated with the results of oral diagnostic challenges with the same foods (soy, cow's milk, and egg white). The geometric mean stimulation index for lymphocytes from patients with positive oral soy protein challenge that were cultured with soy protein was 8.5, and for patients with positive cow's milk challenge the stimulation index was 6.0 when casein was used in the cultures. Both values are significantly different from the values obtained from patients with negative oral challenges (p less than 0.01). The enhanced lymphocyte responses were specific for the food proteins responsible for clinical symptoms. It is not clear whether these lymphocyte responses are due to systemic immunization secondary to macromolecular absorption, or to an abnormality in immune regulation such as a delay in the development of oral tolerance mechanisms. They suggest, however, that circulating lymphocytes sensitive to the food antigens that produce the clinical symptoms are frequent in infants with this discrete form of food protein hypersensitivity.

Functional and structural aspects of the epithelial lymphocyte, with implications for coeliac disease and tropical sprue

Epithelial lymphocytes comprise a compartmentalised and specialised population of presumed effector cells which, in general, express the surface phenotypes (Lyt-2+; OX2+; OKT8+) of suppressor/cytolytic (Ts/c) cells. Granular cells within this population (gEL) morphologically resemble the circulating large granular lymphocytes (LGL) which subserve spontaneous (NK) cytolytic activity. Recent in vitro results indicate that gEL can develop this function after prolonged in vitro culture; the relevance of this, in vivo, remains to be decided. EL also appear to be able to mediate ADCC with sIgA against enteric micro-organisms. This is the kind of integrated activity that might be anticipated from local immunocytes within the intestinal mucosa. Other recent work suggests that gEL are not precursors of mucosal mast cells. EL also appear to be capable of inducing Ia-like expression in surface and crypt enterocytes, a property enjoyed both by highly purified Th, but also Ts/c, cells as well. This raises the interesting prospect that enterocytes may display antigen in macrophage-like fashion to other adjacent cells within the inter-epithelial cell spaces. These latter observations might be more consistent with the presence of 'activated' and 'blast-transformed' lymphocytes in such conditions as coeliac disease and tropical sprue. Another emergent view that demands appropriate attention is that the infiltrate of Ts/c cells into surface, and crypt, epithelium of coeliac mucosa does not necessarily cause injury or damage to the jejunal tissues. Nevertheless the role, either primary or secondary, that EL play either in coeliac disease or tropical sprue still remains obscure.

Cellobiose/mannitol sugar permeability test complements biopsy histopathology in clinical investigation of the jejunum

Intestinal permeability to probe molecules has been shown to correlate closely with the presence or absence of villous atrophy in a jejunal biopsy. The purpose of this study was to establish if there exist groups of patients with functional derangement of intestinal permeability but normal histopathology of the small bowel mucosa. In 135 patients a cellobiose/mannitol permeability test was performed at the same time as jejunal biopsy. Diagnosis included coeliac disease, Crohn's disease, irritable bowel syndrome, idiopathic diarrhoea, self diagnosed food allergy, atopic eczema and postinfectious malabsorption. The value of the cellobiose/mannitol test in identifying patients with abnormal jejunal biopsy histopathology was confirmed. The permeability test was abnormal in all 28 patients with partial or subtotal villous atrophy, and also in all 10 in whom there was a high intraepithelial lymphocyte count despite normal villi and crypts. Functional abnormality of the small intestine has not previously been reported in patients with this jejunal biopsy abnormality. Abnormalities of permeability were also found in patients with idiopathic diarrhoea, folate deficiency, postinfectious or traveller's diarrhoea, small bowel Crohn's disease, and atopic eczema. These results show that sugar permeability tests have more potential in clinical investigation than merely serving as screening tests before jejunal biopsy. There are groups of patients without morphological changes in the small bowel in whom intestinal permeability is abnormal.

Fetal gastric and colonic implants in syngeneic and allogeneic mice developing typical inflammatory changes

Implants of fetal stomach and colon under the kidney capsule of syngeneic, and H-2 compatible and H-2 incompatible allogeneic mice were examined histologically at different time intervals after the procedure. According to the time of implantation typical inflammatory changes were seen in syngeneic stomach and colon implants, which resembled changes seen in chronic atrophic gastritis and chronic ulcerative colitis. Immunofluorescence studies showed that the host developed antibodies against fetal antigens, while there was no evidence for cellular immune response to fetal syngeneic antigens with the direct leukocyte migration inhibition test. Possible explanations for these results are discussed.

Studies of intestinal lymphoid tissue. VI--Proliferative response of small intestinal epithelial lymphocytes distinguishes gluten- from non-gluten-induced enteropathy

Several diseases of the small intestine, including gluten-sensitivity, present with malabsorption and a "flat" mucosa. Determination of the mitotic index of epithelial lymphocytes provides a simple, objective method of assessing, and thus of predicting, whether a flat mucosa is due to gluten-sensitivity (index greater than 0.2%), or not (index less than 0.2%). The use of this index in circumstances especially likely to cause diagnostic confusion--for example, intestinal lymphoma; Crohn's jejunitis of immunodeficiency--is illustrated in this paper. Of seven cases, five (two primary lymphoma, three immunodeficiency) had been treated with a gluten-free diet without benefit; a mitotic index performed on the initial biopsy in each of these patients could have predicted from the outset that none was gluten-sensitive. Of the remaining two cases, determination of the mitotic index on the biopsy initially obtained from a man with severe hypogammaglobulinaemia would have indicated that he was also gluten-sensitive. Empirical use of a gluten-free diet was avoided in the other patient (with flat small intestinal mucosa and low mitotic index) in whom the diagnosis was ultimately shown to be due to Crohn's disease of jejunum.

Hypersensitivity in the small intestinal mucosa. V. Induction of cell-mediated immunity to a dietary antigen

Feeding of a protein antigen to adult mice results in reduced humoral and cell-mediated immune (CMI) responses when that antigen is subsequently presented, and also causes activation of suppressor cells in the gut-associated lymphoid tissues (GALT). We have attempted to abrogate this tolerance to fed antigen by pretreating mice with 100 mg/kg cyclophosphamide before oral immunization and challenge with ovalbumin. Cyclophosphamide-pretreated mice did not develop serum haemagglutinating antibodies, nor systemic CMI (as assessed by skin testing) after ovalbumin feeding. However, evidence that CMI had been induced in the GALT was provided by the significant inhibition of migration and mesenteric lymph node cells from cyclophosphamide-pretreated animals, but not from other control groups. in the presence of ovalbumin. Our previous work on CMI reactions in the small intestine has shown that the cell production rate in the crypts of Lieberkuhn and the intraepithelial lymphocyte count are reliable although indirect measures of mucosal CMI. Cyclophosphamide-pretreated, ovalbumin-immunized animals, which had been fed 0 . 1 mg ovalbumin daily for 10 days before killing, had increased crypt cell mitoses, and increased intraepithelial lymphocyte counts, indicating the presence of mucosal CMI response to ovalbumin. Mechanisms whereby cyclophosphamide pretreatment leads to abrogation of tolerance and induction of mucosal CMI are discussed.

Organ culture of adult mouse intestine. I. Morphological results after 24 and 48 hours of culture

Explants of adult mouse intestine have been maintained in organ culture for 24 to 48 hr. The best results have been obtained with a mixture of DMEM-HEPES medium and NCTC-135 enriched with 10% fetal bovine serum. The morphology of the mucosa is well preserved at the light and electron microscopic level: absorbing cells exhibit an increase in secondary lysosomes; goblet cells and Paneth cells remain active; numerous mitoses are observed in the crypts; and vigorous re-epithelization takes place on the margin of the explants.

Effects of age, antigen deprivation, and allograft rejection on epithelial cell kinetics in mouse colon

A technique of microdissection of colonic mucosa has allowed the study of mitotic activity, measured by metaphase accumulation following colchicine blockade, in individual crypts of mouse colon. The changes occurring during growth and development of normal colon have been studied and compared with changes found in antigen free colon (colonic isografts) and in cell-mediated immune damage of the bowel (allograft rejection). Metaphase accumulation was steady at two metaphases per hour in baby mouse colon until 18 days after birth. Between 18 and 24 days a rapid, and significant increase in mitotic activity occurred (P less than 0.01), reached adult values, and changed no further. Metaphase accumulation in isografts was similar to normal colon for the first two weeks after transplantation but the rise in mitotic activity in the third week did not occur. Allografts of colon showed two- to three-fold increases in metaphase accumulation when compared with both normal colon and isografts (P less than 0.01). When crypt mitotic activity was compared with the length of crypts measured in histological sections of normal colon, isografts, and allografts, no clear relationship was observed. Both changes in the luminal environment of the gut at the time of weaning and cell-mediated immune reactions in the colonic wall appeared to be associated with increased mitotic activity in colonic crypts.

Cell-mediated immunity to gluten fraction III in adult coeliac disease

A migration inhibition test was used to assess sensitisation of blood leucocytes, and thus cell-mediated immunity, to gluten fraction III in controls and patients with coeliac disease. Migration indices were significantly less (indicating sensitisation) in untreated and in treated patients than in controls, and significantly less in treated patients than in untreated patients. At a concentration of 1 mg/ml gluten fraction III, 13% of untreated patients and 54% of treated patients had migration indices in the sensitised range. At 2 mg/ml gluten fraction III, sensitisation was demonstrated in 8% of untreated patients and 48% of treated patients. After starting a gluten free diet, migration indices fell into the sensitised range in all patients followed. After at least nine months on a gluten free diet, migration indices were significantly higher in those patients with a normal interepithelial lymphocyte count than in those patients with a raised interepithelial lymphocyte count. Cell-mediated immunity to gluten fraction III can be detected in the peripheral blood of certain patients with coeliac disease. Detectable sensitivity is related to the time on a gluten free diet, and the interepithelial lymphocyte count.

Effects of local delayed hypersensitivity on the small intestine

There are many T and B cells in the small intestinal mucosa and local T cell immunity could have a role both in protective immunity and as a cause of disease (i.e. hypersensitivity). This latter aspect has been investigated by using several animal models to assess the effects of local delayed hypersensitivity on the structure and function of the small intestine. Heterotopically transplanted grafts of fetal small intestine in mice (isografts and allografts) have been examined by conventional histology, scanning and transmission electron microscopy, by making direct measurements of villi, crypts, and lymphoid cell infiltrate, and by counting the number of mitoses per crypt. This cell-mediated immune reaction causes lymphocyte infiltration which is most marked in the lamina propria, hyperplasia of the crypts of Lieberkühn, increased cell loss with villous atrophy and a flat surface, but the individual enterocytes appear fairly normal. Graft-versus-host disease cause exactly the same changes in structure and in cell kinetics as does rejection. However, crypt hyperplasia has been found to precede villous atrophy by several days. Preliminary experiments on local contact hypersensitivity suggest that intraluminal injection of oxazolone in the gut of sensitized mice also produces villous atrophy and crypt hyperplasia. It is postulated that these effects are likely to be produced via lymphokines: by an 'enteropathic' factor which damages the lamina propria and basement membrane, and a factor which is mitogenic for crypt stem cells. In mice infected with Giardia lamblia, crypt hyperplasia and lymphocyte infiltration of the epithelium are present and there is accelerated epithelial cell turnover. In rats infected with Nippostrongylus brasiliensis, the flat mucosa has been shown to be due to the thymus-dependent immune response and not directly to the damage produced by the parasite itself. A common factor in the variety of conditions associated with villous atrophy and crypt hyperplasia may well be a local cell-mediated immune reaction to food, microbial, parasite or other antigens which causes changes in enterocyte turnover rate and malabsorption.