Cytolytic mechanisms of intraepithelial lymphocytes in coeliac disease (CoD)

Cerebellar presence of immune cells in patients with neuro-coeliac disease

Although various neurodegenerative disorders have been associated with coeliac disease (CD), the underlying neuropathological link between these brain and gut diseases remains unclear. We postulated that the neuronal damage sporadically observed in CD patients is immune-mediated. Our aim was to determine if the loss of neurons, especially Purkinje cells, coincides with microglia activation and T- and B-cell infiltration in the cerebellum of patients with CD and a concomitant idiopathic neurological disease affecting the cerebellum (NeuroCD). Post-mortem cerebellar tissue was collected of validated NeuroCD cases. Gender- and age-matched genetic spinocerebellar ataxia (SCA) controls and non-neurological controls (NNC) were selected based on clinical reports and pathological findings. Cerebellar tissue of seventeen patients was included (6 NeuroCD, 5 SCA, 6 NNC). In SCA cases we found that the Purkinje cell layer was 58.6% reduced in comparison with NNC. In NeuroCD cases this reduction was even more prominent with a median reduction of 81.3% compared to NNC. Marked increased numbers of both CD3+ and CD8+ cells were observed in the NeuroCD but not in SCA patients. This coincided with significantly more microglial reactivity in NeuroCD patients. These findings demonstrate that the massive loss of Purkinje cells in the cerebellum of neuro CD patients is accompanied by local innate and T-cell mediated immune responses.

Colitis nucleomigrans: The third type of microscopic colitis (part 2). An ultrastructural study

In the preceding article (part 1), we proposed the third type of microscopic colitis: colitis nucleomigrans (CN). Microscopically, the nuclei of surface‐lining columnar cells were migrated in chain to the middle part of the cells, and apoptotic nuclear debris was scattered in the cytoplasm beneath the nuclei. For ultrastructural analysis, buffered formalin‐fixed biopsy tissue of CN (n = 2) was dug out of paraffin blocks. After deparaffinization, tissue blocks were prepared with conventional sequences. Ultrathin sections were stained with uranyl acetate and lead citrate. Fine morphological preservation was satisfactory even after paraffin embedding. Apoptotic nuclear debris was localized within the cytoplasm beneath the migrated nuclei of the surface‐lining columnar cells. Abnormality of cytoskeletal filaments (actin, cytokeratin and tubulin) was scarcely recognized in the epithelial cytoplasm. Macrophages located in the uppermost part of the lamina propria phagocytized electron‐dense globular materials. Intraepithelial lymphocytes with scattered dense bodies were observed among the columnar cells. We suppose that altered apoptotic processes in the colorectal surface‐lining epithelial cells may be involved in the pathogenesis of CN. Mechanisms of nuclear migration to the unusual position or impairment of nuclear anchoring to the basal situation in the surface‐lining epithelial cells remain unsettled, because cytoskeletal components showed little ultrastructural abnormality.

Colitis nucleomigrans: The third type of microscopic colitis (part 1)

Microscopic colitis (MC), encompassing collagenous colitis and lymphocytic colitis, is featured by chronic diarrhea, normal‐looking endoscopic findings and unique microscopic appearance. After reviewing biopsied nonspecific colitis, we propose the third type of MC: colitis nucleomigrans (CN). Histopathological criteria of CN included: (i) chained nuclear migration to the middle part of the surface‐lining columnar epithelium; (ii) apoptotic nuclear debris scattered below the nuclei; and (iii) mild/moderate chronic inflammation in the lamina propria. Thirty‐three patients (M:F = 20:13; median age 63 years, range 17–88) fulfilled our criteria. Seven cases demonstrated MC‐like clinical/endoscopic features. Mucosal reddening with or without erosion/aphtha was endoscopically observed in the remaining 26 cases with inflammatory bowel disease (IBD)‐like features: occult/gross hematochezia seen in 19, abdominal pain in two and mucin secretion in two. Cleaved caspase‐3‐immunoreactive apoptotic debris appeared more frequently in IBD‐like CN than in MC‐like CN, while CD8‐positive intraepithelial lymphocytes comparably appeared in both. Proton pump inhibitors (PPIs) were administered in five (71%) cases with MC‐like features, and in three diarrhea improved after drug cessation. In IBD‐like CN cases, eight (31%) received PPIs. Four patients received chemotherapy against malignancies. Four patients associated immune‐related disorders. Microscopic appearance of CN also appeared in a remission state of ulcerative colitis (12/20 lesions).

Therapeutic options for coeliac disease: What else beyond gluten-free diet?

Coeliac disease is a chronic and systemic autoimmune condition triggered by gluten ingestion in genetically predisposed subjects. Currently, the only effective treatment available is a strict, lifelong gluten-free diet. However, patients perceive gluten withdrawal as an unsustainable burden in their life and some of them can exhibit persistent symptoms despite a strict diet. Thus, gluten-free diet represents a challenge, leading scientists to look for alternative or complementary treatments. This review will focus on non-dietary therapies for coeliac disease highlighting six therapeutic strategies: (1) decreasing gluten immunogenic content before it reaches the intestine; (2) sequestering gluten in the gut lumen before absorption; (3) blocking the passage of gluten through a leaky intestinal barrier; (4) preventing the enhancement of immune response against gliadin; (5) dampening the downstream immune activation; (6) inducing immune tolerance to gluten. Most developing therapies are only in the pre-clinical phase with only a few being tested in phase 2b or 3 trials. Although new approaches raise the hope for coeliacs giving them a chance to come back to gluten, for the time being a cautionary appraisal of new therapies suggests that they may have a complementary role to gluten withdrawal, mainly to prevent inadvertent gluten contamination.

Oxidative stress-induced IL-15 trans-presentation in keratinocytes contributes to CD8+ T cells activation via JAK-STAT pathway in vitiligo

Oxidative stress and effector memory CD8⁺ T cells have been greatly implicated in vitiligo pathogenesis. However, the crosstalk between these two crucial pathogenic factors has been merely investigated. IL-15 has been regarded as an important cytokine exerting its facilitative effect on memory CD8⁺ T cells function in various autoimmune diseases. In the present study, we initially discovered that the IL-15 expression was significantly increased in vitiligo epidermis and highly associated with epidermal H₂O₂ content. In addition, epidermal IL-15 expression was mainly derived from keratinocytes. Then, we showed that oxidative stress promoted IL-15 and IL-15Rα expression as well as IL-15 trans-presentation by activating NF-κB signaling in keratinocytes. What's more, the trans-presented IL-15, rather than the secreted one, was accounted for the potentiation of CD8⁺ T_EMs activation. We further investigated the mechanism underlying trans-presented IL-15 in potentiating CD8⁺ T_EMs activation and found that the blockage of IL-15-JAK-STAT signaling could be a potent therapeutic approach. Taken together, our results demonstrate that oxidative stress-induced IL-15 trans-presentation in keratinocytes contributes to the activation of CD8⁺ T_EMs, providing a novel mechanism by which oxidative stress initiates autoimmunity in vitiligo.

Evolving Therapy for Celiac Disease

Gluten is known to be the main triggering factor for celiac disease (CeD), an immune-mediated disorder. CeD is therefore managed using a strict and lifelong gluten-free diet (GFD), the only effective treatment available currently. However, the GFD is restrictive. Hence, efforts are being made to explore alternative therapies. Based on their mechanisms of action on various molecular targets involved in the pathogenesis of CeD, these therapies may be classified into one of the following five broad approaches. The first approach focuses on decreasing the immunogenic content of gluten, using strategies like genetically modified wheat, intra-intestinal gluten digestion using glutenases, microwave thermal treatment of hydrated wheat kernels, and gluten pretreatment with either bacterial/ fungal derived endopeptidases or microbial transglutaminase. The second approach involves sequestering gluten in the gut lumen before it is digested into immunogenic peptides and absorbed, using binder drugs like polymer p(HEMA-co-SS), single chain fragment variable (scFv), and anti- gluten antibody AGY. The third approach aims to prevent uptake of digested gluten through intestinal epithelial tight junctions, using a zonulin antagonist. The fourth approach involves tissue transglutaminase (tTG) inhibitors to prevent the enhancement of immunogenicity of digested gluten by the intestinal tTG enzyme. The fifth approach seeks to prevent downstream immune activation after uptake of gluten immunogenic peptides through the intestinal mucosal epithelial layer. Examples include HLA-DQ2 blockers that prevent presentation of gluten derived- antigens by dendritic cells to T cells, immune- tolerizing therapies like the vaccine Nexvax2 and TIMP-Glia, cathepsin inhibitors, immunosuppressants like corticosteroids, azathioprine etc., and anti-cytokine agents targeting TNF-α and interleukin-15. Apart from these approaches, research is being done to evaluate the effectiveness of probiotics/prebiotics, helminth therapy using Necator americanus, low FODMAP diet, and pancreatic enzyme supplementation in CeD symptom control; however, the mechanisms by which they play a beneficial role in CeD are yet to be clearly established. Overall, although many therapies being explored are still in the pre-clinical phase, some like the zonulin antagonist, immune tolerizing therapies and glutenases have reached phase II/III clinical trials. While these potential options appear exciting, currently they may at best be used to supplement rather than supplant the GFD.

The elusive case of human intraepithelial T cells in gut homeostasis and inflammation

The epithelial barrier of the gastrointestinal tract is home to numerous intraepithelial T cells (IETs). IETs are functionally adapted to the mucosal environment and are among the first adaptive immune cells to encounter microbial and dietary antigens. They possess hallmark features of tissue-resident T cells: they are long-lived nonmigratory cells capable of rapidly responding to antigen challenges independent of T cell recruitment from the periphery. Gut-resident T cells have been implicated in the relapsing and remitting course and persisting low-grade inflammation of chronic gastrointestinal diseases, including IBD and coeliac disease. So far, most data IETs have been derived from experimental animal models; however, IETs and the environmental makeup differ between mice and humans. With advances in techniques, the number of human studies has grown exponentially in the past 5 years. Here, we review the literature on the involvement of human IETs in gut homeostasis and inflammation, and how these cells are influenced by the microbiota and dietary antigens. Finally, targeting of IETs in therapeutic interventions is discussed. Broad insight into the function and role of human IETs in gut homeostasis and inflammation is essential to identify future diagnostic, prognostic and therapeutic strategies.

Mesenchymal stem cells as potential therapeutic approaches in celiac disease

As a chronic immune complication, celiac disease has a broad spectrum of clinical manifestations and gluten ingestion as an external trigger will induce the onset of this disease in genetically predisposed individuals. Because of the complex nature of celiac disease and various cascades of immunological pathways, therapies which are tend to target a single pathway or factor, often have unsatisfactory results. Thus, it should be considered that the new emerging area of cellular therapy by targeting multiple pathways may hold the key for treating celiac affected patients with complicated forms of this disease. The aim of this review is to discuss different pathways which are affected by celiac disease and to compare how various strategies, mainly cellular therapies, can regulate these pathways.

Distribution and Activation of CD8+ T Cells in the Duodenal Mucosa before and after HIV Seroconversion

CD8⁺ T cells in the intestinal mucosa influence the HIV-associated pathogenesis, but little is known about the dynamics of mucosal CD8⁺ T cell counts and activation of these cells during the course of infection. In this study, mucosal CD8⁺ T cells in the duodenum were studied at different stages of HIV infection, starting from the seronegative phase. In seronegative acute HIV infection, CD8⁺ T cell counts increased in the epithelium, but not in the lamina propria. Infiltration of the lamina propria by peripherally expanded CD8⁺ T cells was observed after seroconversion. Highest increase in the expression of perforin, the rate-limiting molecule for cytotoxic CD8⁺ T cell activity, was evident in the lamina propria of seronegative acutely HIV-infected patients. The number of perforin-expressing cells in the lamina propria of acutely HIV-infected patients was positively associated with biomarkers of enterocyte damage and microbial translocation. After seroconversion, perforin expression was downregulated in the lamina propria, but not in the epithelium. In conclusion, our findings demonstrate that intraepithelial and lamina propria CD8⁺ T cells exhibit different dynamics of numerical alteration and cytotoxic activity in HIV-infected patients. Moreover, our results suggest that perforin-dependent cytotoxic mechanisms by CD8⁺ T cells could impair the intestinal mucosal barrier already in the seronegative phase of acute HIV infection, thereby inducing microbial translocation as one of the earliest pathological events in HIV infection.

Are stem cells a potential therapeutic tool in coeliac disease?

Despite the growing understanding of its pathogenesis, the treatment of coeliac disease is still based on a lifelong gluten-free diet that, although efficacious, is troublesome for affected patients, and a definitive cure is still an unmet need. In this regard, the development of new chemical- and biological-derived agents has often resulted in unsatisfactory effects when tested in vivo, probably because of their ability to target only a single pathway, whilst the immunological cascade responsible for tissue injury is complex and redundant. The advent of cellular therapies, mainly based on the use of stem cells, is an emerging area of interest since it has the advantage of a multi-target strategy. Both haematopoietic and mesenchymal stem cells have been employed in the treatment of refractory patients suffering from autoimmune diseases, with promising results. However, the lack of immunogenicity makes mesenchymal stem cells more suitable than their haematopoietic counterpart, since their transplantation may be performed in the absence of a myeloablative conditioning regimen. In addition, mesenchymal stem cells have been shown to harbour strong modulatory effects on almost all cells involved in immune response, together with a potent regenerative action. It is therefore conceivable that over the next few years their therapeutic use will increase as their biological interactions with injured tissues become clearer.

Immune responses to HIV and SIV in mucosal tissues: 'location, location, location'

PURPOSE OF REVIEW

This review summarizes research literature regarding mucosal immunity to HIV and simian immunodeficiency virus (SIV), with an emphasis on work published within the past 18 months.

RECENT FINDINGS

Notable recent studies have focused on the pivotal events occurring within mucosal tissues during acute HIV/SIV infection that serve to establish a balance between detrimental immune activation and beneficial adaptive responses. In cervicovaginal mucosa, an early inflammatory response leads to recruitment of susceptible target cells. At this acute stage, the in-vivo ratio between CD8 effector cells and infected CD4 T-cells may be critical for limiting viral dissemination. Acute infection is also accompanied by loss of germinal center architecture and T/B cell apoptosis in Peyer's patches of the gastrointestinal tract. During chronic infection, mucosal CD8 T-cells may play a role in immune control, as suggested by studies of elite controllers.

SUMMARY

Mucosal tissues serve as the major portal of entry for HIV, and house a majority of the body's lymphocytes, including CD4 T-cells that are targets for infection. Recent studies have focused renewed attention on events occurring immediately after transmission, and underscore the concept that the balance between inflammation and protective immunity is established by host responses in mucosal tissues.

Celiac disease: from pathogenesis to novel therapies

Celiac disease has become one of the best-understood HLA-linked disorders. Although it shares many immunologic features with inflammatory bowel disease, celiac disease is uniquely characterized by (1) a defined trigger (gluten proteins from wheat and related cereals), (2) the necessary presence of HLA-DQ2 or HLA-DQ8, and (3) the generation of circulating autoantibodies to the enzyme tissue transglutaminase (TG2). TG2 deamidates certain gluten peptides, increasing their affinity to HLA-DQ2 or HLA-DQ8. This generates a more vigorous CD4(+) T-helper 1 T-cell activation, which can result in intestinal mucosal inflammation, malabsorption, and numerous secondary symptoms and autoimmune diseases. Moreover, gluten elicits innate immune responses that act in concert with the adaptive immunity. Exclusion of gluten from the diet reverses many disease manifestations but is usually not or less efficient in patients with refractory celiac disease or associated autoimmune diseases. Based on the advanced understanding of the pathogenesis of celiac disease, targeted nondietary therapies have been devised, and some of these are already in phase 1 or 2 clinical trials. Examples are modified flours that have been depleted of immunogenic gluten epitopes, degradation of immunodominant gliadin peptides that resist intestinal proteases by exogenous endopeptidases, decrease of intestinal permeability by blockage of the epithelial ZOT receptor, inhibition of intestinal TG2 activity by transglutaminase inhibitors, inhibition of gluten peptide presentation by HLA-DQ2 antagonists, modulation or inhibition of proinflammatory cytokines, and induction of oral tolerance to gluten. These and other experimental therapies will be discussed critically.

Gliadin activates HLA class I-restricted CD8+ T cells in celiac disease intestinal mucosa and induces the enterocyte apoptosis

BACKGROUND & AIMS

The extensive infiltration of CD8(+) T cells in the intestinal mucosa of celiac disease (CD) patients is a hallmark of the disease. We identified a gliadin peptide (pA2) that is selectively recognized by CD8(+) T cells infiltrating intestinal mucosa of HLA-A2(+) CD patients. Herein, we investigated the phenotype, the tissue localization, and the effector mechanism of cells responsive to pA2 by using the organ culture of CD intestinal mucosa. The target of pA2-mediated cytotoxicity was also investigated by using the intestinal epithelial cell lines Caco2 and HT29, A2(+) and A2(-), respectively, as target cells.

METHODS

Jejunal biopsy specimens from CD patients were cultured in vitro with pA2, and cellular activation was evaluated by immunohistochemistry and cytofluorimetric analysis. Cytotoxicity of pA2-specific, intestinal CD8(+) T cells was assayed by granzyme-B and interferon-gamma release and by apoptosis of target cells.

RESULTS

pA2 challenge of A2(+) CD mucosa increased the percentage of CD8(+)CD25(+) and of CD80(+) cells in the lamina propria, the former mainly localized beneath the epithelium, as well as the number of terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling-positive cells (TUNEL(+)) in the epithelium. Intraepithelial CD3(+) cells and enterocyte expression of Fas were also increased. CD8(+)CD25(+) and CD8(+)FASL(+) T cells were significantly increased in cell preparations from biopsy specimens cultured with pA2. CD8(+) T-cell lines released both granzyme-B and interferon-gamma following recognition of pA2 when presented by Caco2 and not by HT29.

CONCLUSIONS

These data indicate that gliadins contain peptides able to activate, through a TCR/HLA class I interaction, CD8-mediated response in intestinal CD mucosa and to induce the enterocyte apoptosis.

The intestinal intraepithelial lymphocytes with t cell receptor alphabeta express toll-like receptor 4 and are responsive to lipopolysaccharide

BACKGROUND

Intestinal intraepithelial lymphocytes (iIELs) play an important role in intestinal innate immunity and oral immune tolerance. To compare the differences in gene expression between murine iIELs and splenic T lymphocytes, we established the cDNA subtractive library of iIELs and analyzed the iIELs special genes. Our study focused on the relationship between Toll-like receptor 4 (TLR4), TLR5 and iIELs.

METHODS

Ninety percent purified iIELs and splenic T lymphocytes were isolated by density-gradient centrifugation in a Percoll and nylon column, respectively. We then established the cDNA subtractive library of iIELs via improved subtractive hybridization. The special expressed sequence tags of iIELs were screened by reverse Northern blot. The expressions of TLR4 and TLR5 were analyzed by RT-PCR and fluorescence staining. The proliferation of T cells was determined by (3)H-TdR incorporation.

RESULTS

TLR4, but not TLR5, was detected in iIELs by RT-PCR and fluorescence staining. However, TLR4 was only found in alphabeta iIELs. Furthermore, iIELs were observed to proliferate in response to lipopolysaccharide in vitro, with upregulation of IRAK-1 mRNA expression.

CONCLUSION

alphabeta iIELs can recognize lipopolysaccharide via TLR4, which may play an important role in the intestinal innate immunity.

Regulation of apoptosis during homeostasis and disease in the intestinal epithelium

A single epithelial layer serves as the interface between the organism and the contents of the gastrointestinal tract, underlining the importance of regulating cellular viability despite an onslaught of pathogens, toxins, waste by-products, and cytokines. A balance between cellular proliferation and apoptosis is necessary to maintain this critical barrier. Recent findings have begun to explain the mechanisms by which intestinal epithelial cells are able to survive in such an environment and how loss of normal regulatory processes may lead to inflammatory bowel disease (IBD) and predispose to inflammation-associated neoplasia. This review focuses on the regulation of physiological apoptosis in development and homeostasis and on pathological apoptosis in intestinal disease, inflammation, and neoplasia, identifying remaining questions and areas of needed investigation.

Epithelium derived interleukin 15 regulates intraepithelial lymphocyte Th1 cytokine production, cytotoxicity, and survival in coeliac disease

BACKGROUND AND AIMS

Epithelium derived interleukin (IL)-15 signalling via IL-15Ralpha is critical for the development, activation, and survival of intraepithelial lymphocytes (IEL). We aimed to better understand the IL-15 driven effects on IEL underlying mucosal damage and lymphomagenesis in coeliac disease (CD).

METHODS

Enterocytes, IEL, and lamina propria mononuclear cells (LPMC) were isolated from 46 patients with uncomplicated CD (25 untreated and 21 treated) and 22 controls. IL-15 and IL-15Ralpha expression were determined by immunoblotting. Secretion of IL-15, interferon gamma (IFN-gamma), tumour necrosis factor alpha (TNF-alpha), and granzyme B into cell culture supernatants was assessed by ELISA. The ability of IL-15 to regulate IEL proliferation, perforin/granzyme dependent cytotoxicity, and apoptosis was tested by adding different combinations of IL-15, IL-15 blocking antibody, or chloroquine to IEL cultured alone or with Caco-2 cells as target. IL-15 mucosal levels were also determined by ELISA in five patients with complicated CD (two ulcerative jejunoileites, one refractory sprue, and two enteropathy associated T cell lymphomas) tested for T cell receptor gamma chain clonality.

RESULTS

IL-15 was overexpressed in untreated CD enterocytes and LPMC, and in the mucosa of complicated CD patients and uncomplicated untreated CD patients, where its levels correlated with the degree of mucosal damage. Enterocytes from untreated, but not treated, CD patients and controls secreted IL-15. Untreated CD IEL, characterised by higher IL-15Ralpha expression, showed increased proliferation, production of IFN-gamma and TNF-alpha, and perforin/granzyme dependent cytotoxicity, and a decreased propensity to apoptosis in response to IL-15.

CONCLUSIONS

Our findings suggest that IL-15 plays a crucial role in the generation of epithelial damage in active CD. Its promotion of IEL survival in CD may predispose to the emergence of T cell clonal proliferations. Blocking IL-15, by suppressing uncontrolled IEL activation and survival, has the potential to provide new therapeutic tools to prevent tissue damage and lymphomagenesis in CD.

Duodenal cytotoxic lymphocytes in cow's milk protein sensitive enteropathy and coeliac disease

OBJECTIVE

Pathogenetic mechanisms of cow's milk protein-sensitive enteropathy (CMSE) are poorly defined, but elevated serum granzyme levels and an increase in duodenal intraepithelial lymphocytes (IELs) expressing TIA-1 suggest the involvement of abnormal lymphocyte cytotoxicity. To evaluate cytotoxicity in CMSE we analysed the expression of cytotoxic granule components in duodenal IELs. For comparison, we studied subjects with coeliac disease (CD), in which lymphocyte cytotoxicity is pathogenically important.

MATERIAL AND METHODS

Fifty-four children were examined by endoscopy for gastrointestinal complaints. Twenty-one subjects had a final diagnosis of CMSE, 15 children had untreated CD and 18 controls showed no definite gastrointestinal disease. Mucosal samples furnished from the bulb and descending duodenum were stained for CD3, perforin, granzymes A and B and TIA-1.

RESULTS

In both CMSE and CD, increase of mid-duodenal TIA-1, perforin and granzyme A expressing IELs was seen, the counts in CD being much higher, and increased expression was also seen in the bulb. Granzyme B expression was increased only in CD. In CMSE, no evidence of villous atrophy was seen.

CONCLUSIONS

Increase in duodenal IELs expressing cytotoxic granules is a characteristic feature in CMSE, although to a lesser degree than in CD. Cytotoxicity is suggested to be involved in the pathogenesis of intestinal dysfunction in CMSE, but based on the absence of villous abnormalities may not be mainly targeted to enterocytes. The mechanisms leading to the accumulation of these cells in CMSE need further investigation.

"Coelionomics": towards understanding the molecular pathology of coeliac disease

Coeliac disease (CD) is an inflammatory disorder of the small intestine characterised by a permanent intolerance to gluten-derived peptides. When gluten-derived peptides reach the lamina propria in CD patients, they provoke specific changes in the mucosa of their small intestine. Although the susceptibility to CD is strongly determined by environmental gluten, it is clearly a common genetic disorder. Important genetic factors for CD are the HLA-DQ genes located in the MHC region on chromosome 6 [HLA-DQ2 (95%) or HLA-DQ8 ( approximately 5%) heterodimers]. So far, the only treatment for CD consists of a life-long gluten-free diet. A key question in CD is why the gluten-derived peptides are resistant to further breakdown by endogenous proteases and how, in turn, they can activate a harmful immune response in the lamina propria of genetically predisposed individuals. Four mechanisms, namely apoptosis, oxidative stress, matrix metalloproteinases and dysregulation of proliferation and differentiation, are thought to play a role in the pathophysiology of CD. Whether the genes involved in these four mechanisms play a causative role in the development of the villous atrophy or are, in fact, a consequence of the disease process is unknown. In this review we summarise these mechanisms and discuss their validity in the context of current insights derived from genetic, genomic and molecular studies. We also discuss future directions for research and the therapeutic implications for patients.

Cytotoxic T cells are preferentially activated in the duodenal epithelium from patients with florid coeliac disease

Villous atrophy and increased numbers of intraepithelial T cells in duodenal biopsies represent a hallmark of coeliac disease. In the present study, an attempt has been made to define whether cytotoxic cell subsets are activated in situ in the affected mucosa of susceptible individuals early after ingestion of a gluten-containing diet. Duodenal biopsies from 11 patients with coeliac disease who repeatedly underwent endoscopic biopsy after ingestion of individually dosed amounts of gluten were used for immunohistochemistry and in situ hybridization. To identify the cell subsets expressing perforin mRNA and protein, in situ hybridization and FACS analyses were performed on cells isolated from fresh biopsies. Compared with normal mucosa, the number of intraepithelial lymphocytes containing perforin mRNA and protein increased significantly in tissue samples showing moderate or florid coeliac disease and closely paralleled the severity of morphological alteration, whereas the frequency of perforin-expressing lamina propria lymphocytes increased only moderately. Cells isolated from florid biopsies that expressed perforin mRNA and protein were preferentially T-cell receptor (TCR) alphabeta T cells. The increase in both the absolute number and the percentage of lymphocytes expressing perforin mRNA indicates in situ activation of lymphocytes within the epithelial compartment in florid coeliac disease upon ingestion of a gluten-containing diet in patients predisposed to coeliac disease.

IL-15 converts human intestinal intraepithelial lymphocytes to CD94 producers of IFN-gamma and IL-10, the latter promoting Fas ligand-mediated cytotoxicity

Intestinal intraepithelial lymphocytes (IELs), T-cell receptor alphabeta(+) CD8(+) T cells located between epithelial cells, are thought to contribute to Fas ligand (FL)-mediated epithelial cell death in coeliac disease, a condition characterized by excess interleukin-15 (IL-15). This study evaluates the effects of prolonged IL-15 stimulation on IELs. Human IELs were obtained from jejunal mucosa from gastric bypass operations for morbid obesity and cultured for 3 or 10 days with IL-15. As the culture progressed, an increasing number of IELs became CD94(+) and produced massive quantities of interferon-gamma (IFN-gamma) and IL-10. There was a steady rate of transcription with no feedback regulation. Few chronically activated IELs produced IL-2, IL-4, or tumour necrosis factor-alpha (TauNuF-alpha). To determine whether the accumulation of IL-10 affected IEL functions, endogenous IL-10 was neutralized by antibody during culture with IL-15. This manipulation reduced expression of CD94, NKG2D, and FL as well as FL-mediated killing of Jurkat cells by IELs. It did not affect perforin or TNF-alpha expression or the associated cytotoxic activities. This study shows that IL-15 induces the development of CD94(+) IELs containing IFN-gamma and IL-10, and that endogenous IL-10 promotes FL-mediated cytotoxicity.

Anti-CD3 induces bi-phasic apoptosis in murine intestinal epithelial cells: possible involvement of the Fas/Fas ligand system in different T cell compartments

Recent studies have suggested that Fas-mediated apoptosis is involved in the pathogenesis of intestinal injury. In this study, we determined the role of Fas/Fas ligand (FasL) interactions in different T cell compartments using a murine model of small intestinal injury. An intraperitoneal injection of 145-2C11 (anti-CD3) antibody into C3H/HeN, BALB/c and MRL mice induced mucosal flattening and rapid, bi-phasic intestinal epithelial cell (IEC) apoptosis, which was detected by conventional light and electron microscopy and by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling. In the first, early phase, villous apoptosis was observed up to 4 h after injection, and in the second, later phase, apoptotic crypt cells gradually accumulated for up to 24 h. The early and later phases of apoptosis were reduced in lpr/lpr and nude mice compared with those in control strains. In addition, the kinetics of Fas-mediated killer activity induced by the antibody injection were different between intestinal intraepithelial lymphocytes (IEL) and splenocytes (SPL) and seemed to correlate with the bi-phasic occurrence of the apoptosis. Finally, the transfer of intestinal IEL from euthymic to nude mice induced both phases of apoptosis, whereas SPL induced the second phase's crypt apoptosis only by the antibody injection. Together, these results suggest the involvement of Fas-mediated killer activity of thymus-derived T cells in different compartments. Namely, T cell populations in different compartments are differentially involved in the induction of IEC apoptosis and contribute to the complex pathogenesis of immune-mediated intestinal injury in which Fas/FasL interactions may play a critical role.

Evidence for increased apoptosis of duodenal intraepithelial lymphocytes in cow's milk sensitive enteropathy

OBJECTIVES

Enterocyte apoptosis induced by activated intraepithelial lymphocytes (IELs) is increased in celiac disease (CD). A lesser increment in intraepithelial lymphocytes associated with normal villous structure is also characteristic of cow's milk sensitive enteropathy (CMSE), but no information is available about the apoptosis rate of this condition.

METHODS

Endoscopic biopsy samples of 21 children with untreated CMSE were compared with samples from 15 children with CD and 18 controls. Apoptosis was analyzed using the TUNEL technique and the M30 antibody from duodenal bulb and mid-duodenum samples. Ki-67 was used to detect the proliferation rate and CD3(+) to count the overall number of T lymphocytes.

RESULTS

In the mid-duodenum, CMSE patients showed a significantly increased intraepithelial and lamina propria density of TUNEL(+) cells, but no difference in the density of M30(+) epithelial cells was seen compared with controls. In CD subjects, TUNEL(+) counts in mid-duodenal villous epithelium were increased. CD3(+) intraepithelial lymphocytes were increased in both CMSE and CD and correlated with TUNEL(+) and M30(+) counts among all patients. No increase in proliferation rate was seen in CMSE, and no significant correlations between apoptosis and proliferation rates were detected.

CONCLUSIONS

The observed increase in TUNEL(+) counts and the absence of any increase in M30(+) cells suggest that the apoptosis rate of intraepithelial lymphocytes, but not of enterocytes, is increased in the small IELs in CMSE. However, the number of intraepithelial lymphocytes is still elevated in CMSE, indicating that a disturbance of homeostasis of intraepithelial lymphocytes is important in its pathogenesis.

Interleukin-12 up-regulates perforin- and Fas-mediated lymphokine-activated killer activity by intestinal intraepithelial lymphocytes

Human intraepithelial lymphocytes (IELs) comprise a unique compartment of memory T cell receptor (TCR)-alphabeta( +)CD8(+) T lymphocytes interspersed between intestinal epithelial cells. They develop potent lymphokine-activated killer (LAK) activity with interleukin (IL)-15, a cytokine that is found in excess in certain mucosal inflammatory states. IL-12, released by activated antigen-presenting cells, is known to potentiate perforin-induced cytotoxicity. This study evaluates the mechanism by which IL-12 up-regulates LAK activity. When IELs were stimulated with IL-15, the CD94(+) IEL subset expanded and carried out cytotoxic activity in redirected lysis against P815 cells as well as Fas ligand (FL)- and tumour necrosis factor (TNF)-alpha-mediated lysis of Jurkat and WEHI cells, respectively. IL-12 enhanced the perforin- and FL-, but not TNF-alpha-mediated events. In addition, the up-regulated killing of HT-29 cells by IL-12 was reduced by concanamycin (which targets perforin) and antibody neutralizing FL but not by anti-TNF-alpha antibody. Furthermore, IL-12 augmented IL-15-stimulated release of serine esterases as well as expression of perforin and FL by IELs, but not TNF-alpha. This study shows that LAK activity, carried out by the CD94(+) IELs, involves perforin, FL and TNF-alpha. IL-12 up-regulates the first two mechanisms of action, showing for the first time its effect on FL production and lytic activity.

Cytolytic capabilities of lamina propria and intraepithelial lymphocytes in normal and chronically inflamed human intestine

Cell-mediated lymphocyte cytotoxicity in ileum and colon of patients with ulcerative colitis (UC), Crohn's disease (CD) and controls was investigated. Frequencies of cells expressing perforin and Fas-ligand (FasL) were determined by immunomorphometry. mRNA expression of perforin, granzyme B and FasL in T cells and subsets was assayed by reverse transcriptase-polymerase chain reaction. Cytotoxicity of intraepithelial and lamina propria lymphocytes was analysed without ex vivo activation in three functional assays: (1) anti-CD3-dependent T-cell receptor (TCR)-/CD3-mediated redirected cytotoxicity, (2) Fas-/FasL-mediated TCR-/CD3-independent cytotoxicity and (3) natural killer (NK) cell cytotoxicity. Inflammation in ileum of CD patients caused increased frequency of perforin-expressing cells and enhanced perforin-dependent TCR-/CD3-mediated cytotoxicity. In contrast, lymphocytes in the inflamed colon of UC or Crohn's colitis patients did not display this cytotoxicity nor did lymphocytes of normal colon. Normal colon lymphocytes showed spontaneous Fas-/FasL-mediated cytotoxicity. This activity was retained but not enhanced in inflamed UC colon. In contrast, a significant increase of FasL-expressing cells was seen in situ. Inflammation did not induce NK cell activity in colonic lymphocytes. Intestinal lymphocytes comprise effectors active in two different cytolytic processes. 'Classical' cytotoxic T lymphocytes in small intestine and lymphocytes executing TCR-/CD3-independent FasL-/Fas-mediated killing of unknown biological role present throughout the intestinal mucosa. Ongoing normal cytolytic processes seem to be enhanced by chronic inflammation.

Abundant expression of granzyme A, but not perforin, in granules of CD8+ T cells in GALT: implications for immune control of HIV-1 infection

Because GALT is a major portal of entry for HIV-1 and reservoir for viral replication, we hypothesized that an ineffective cellular immune response in intestinal mucosa might partially explain the failure of immune control in AIDS. In this study, we demonstrate that the vast majority of CD8+ T cells in rectal tissue, including HIV-1-specific cells, fail to express the cytolytic protein, perforin. However, rectal CD8+ T cells do express granzyme A, and are also capable of releasing IFN-gamma upon stimulation with cognate peptide. Confocal microscopy showed that granzyme A was located in intracellular granules in the absence of perforin. The majority of rectal CD8+ T cells exhibit an effector memory phenotype, expressing CD45RO but not CCR7. Quantitative real-time PCR analysis demonstrated that perforin RNA is expressed in rectal CD8+ T cells from healthy and HIV-1-positive individuals. In HIV-1-positive individuals, similar amounts of perforin RNA were detected in CD8+ T cells from rectal tissue and PBMC, despite a relative absence of perforin protein in rectal tissue. These findings demonstrate an important difference in perforin expression between CD8+ T cells in blood and mucosa. Furthermore, the relative absence of armed effector cells may serve to protect the integrity of rectal mucosa under normal conditions, but might also provide an early advantage to HIV-1 and other sexually transmitted viruses.

Immunohistochemical study of the apoptotic mechanisms in the intestinal mucosa during children's coeliac disease

Mechanisms leading to morphological changes of the small intestine during coeliac disease (CD) are not yet completely recognized; however, two main processes have been suggested recently: remodeling of mucosa by matrix metalloproteinases, and mucosal atrophy by apoptosis. The aim of this study was analysis of the expression of proteins regulating apoptosis in the small intestine of children with active CD (ACD) and potential CD (PCD). Jejunal biopsies of 43 children with PCD and untreated ACD and 21 control samples were analyzed by means of standard indirect immunohistochemical technique for Fas, Fas ligand (Fas-L), tissue transglutaminase (tTG), Bcl-2, and glutathione S-transferase (GST) expression. We found significantly lower numbers of Fas-expressing enterocytes in the ACD patients than in PCD patients and controls. Similarly, the number of Fas-positive mucosal lymphocytes was decreased in ACD when compared with PCD. The number of Fas-L- and tTG-expressing enterocytes and mucosal lymphocytes was higher in both PCD and ACD. On the other hand, the number of Bcl-2-positive mucosal lymphocytes in PCD as well as ACD was significantly lower. The expression of tTG in extracellular matrix was significantly higher in PCD and ACD when compared with controls. Our results showed that Fas and/or Fas-L, Bcl-2, and tTG may be involved in apoptotic pathways leading to mucosal atrophy in children with CD. tTG changes are in agreement with the presumed role of this protein in the pathogenesis of CD.

Celiac disease association with CD8+ T cell responses: identification of a novel gliadin-derived HLA-A2-restricted epitope

One of the diagnostic hallmarks of the histological lesions associated with celiac disease is the extensive infiltration of the small intestinal epithelium by CD8(+) T cells of unknown Ag specificity. In this study, we report recognition of the gliadin-derived peptide (A-gliadin 123-132) by CD8(+) T lymphocytes from celiac patients. A-gliadin 123-132-specific IFN-gamma production and cytotoxic activity were detected in PBMCs derived from patients on gluten-free diet, but not from either celiac patients on gluten-containing diet or healthy controls. In contrast, A-gliadin 123-132-specific cells were isolated from small intestine biopsies of patients on either gluten-free or gluten-containing diets. Short-term T cell lines derived from the small intestinal mucosa and specific for the 123-132 epitope recognized human APC pulsed with either whole recombinant alpha-gliadin or a partial pepsin-trypsin gliadin digest. Finally, we speculate on a possible mechanism leading to processing and presentation of class I-restricted gliadin-derived epitopes in celiac disease patients.

Coeliac disease

In the last few decades, the comprehension of epidemiological, pathogenic and clinical aspects of coeliac disease has increasingly improved. Serological screening studies on the general population have shown that the true coeliac disease prevalence in Europe is higher than previously reported. It has become clear that tissue transglutaminase has a crucial role in the pathogenesis of coeliac disease pathogenesis, and there is evidence that substitution of deamidated amino acidic residues at a critical position along the gliadin sequence dramatically increases immunological activation. The toxicity of many gluten epitopes has been investigated, so far, but recent studies have indicated the region 57-75 of alpha gliadin as a possible candidate epitope in the pathogenesis of coeliac disease. However, the wide heterogeneity of gliadin and glutenin molecules complicate any attempts to identify the toxic epitope, and the fascinating idea to produce detoxified grains will represent a great challenge in the near future. From a clinical point of view, there is now evidence of a broad spectrum of gluten conditions. Extra-intestinal signs, i.e., alopecia, unexplained neurological disorders, cryptic hypertransaminasaemia, increased red cell width, frequently constitute the only clinical manifestation at the diagnosis.

Defining the roles of perforin, Fas/FasL, and tumour necrosis factor alpha in T cell induced mucosal damage in the mouse intestine

BACKGROUND AND AIMS

Mucosal flattening and epithelial cell apoptosis are typical features of T cell induced inflammatory diseases of the bowel, such as coeliac disease and graft versus host disease. Mice injected with a T cell activating anti-CD3 antibody develop a severe diarrhoeal illness. We describe the histological features of this enteropathy and define the effector mechanisms involved in T cell induced mucosal injury in this in vivo model.

METHODS

Wild-type and genetically modified mice were injected with the anti-CD3 antibody 3C11 (50 microg). Changes in the murine intestine were characterised by light microscopy analysis and terminal uridine nick-end labelling (TUNEL) assay. The role of perforin, Fas/Fas ligand (FasL), tumour necrosis factor alpha (TNF-alpha), and interferon gamma (IFN-gamma) in T cell induced mucosal damage was assessed using selected immunodeficient mouse strains.

RESULTS

T cell activation caused severe damage, including small intestinal mucosal flattening and apoptosis of crypt epithelial cells. Mucosal damage was unaltered in anti-CD3 treated mice lacking IFN-gamma, Fas, or TNF-alpha receptors. In mice lacking TNF-alpha receptors and Fas (TNF-R1xR2 lpr/lpr strain), enterocyte apoptosis was diminished but there was no significant reduction in tissue damage. Apoptosis and mucosal injury were significantly reduced in perforin knockout mice. Abrogation of both FasL and perforin (perforin KOxgld mice) further significantly reduced tissue damage and apoptotic bodies.

CONCLUSIONS

T cell induced mucosal injury is mediated by the combined effect of multiple pathways but predominantly by perforin. The redundancy of the mechanisms of tissue damage will have significant impact on therapeutic strategies aimed at specific and targeted inhibition of inflammatory processes.

Mechanisms of villous atrophy in autoimmune enteropathy and coeliac disease

Since in coeliac disease mucosal flattening has been suggested to result from an increased enterocyte apoptosis triggered by Fas/Fas ligand system and perforin cytolytic granules, we looked for a similar mechanism in autoimmune enteropathy. Moreover, we tried to assess whether enterocyte autoantibodies, which are the hallmark of autoimmune enteropathy, may be involved in triggering enterocyte apoptosis in this condition. Immunohistochemical staining with anti-Fas, -FasL and -perforin MoAb, and TUNEL technique were applied on endoscopic duodenal biopsies of two autoimmune enteropathy patients, two untreated coeliac patients and two biopsied controls. Cytotoxicity assays were carried out by incubating peripheral blood mononuclear cells from a healthy subject (effectors) with enterocytes primed with patient or control sera (targets). In autoimmune enteropathy a large number of enterocytes were apoptotic, as in coeliac disease, whereas neither Fas/Fas ligand or perforin expressions were up-regulated. On the other hand, antibody-dependent cellular cytotoxicity assay revealed the ability of sera from patients with autoimmune enteropathy to mediate enterocyte death through apoptosis. These results point to enterocyte autoantibody-dependent cellular cytotoxicity as the prevalent mechanism of increased enterocyte apoptosis in autoimmune enteropathy but not in coeliac disease.

Update on immunologic basis of celiac disease

During the past few years several seminal studies have greatly expanded our knowledge on celiac disease pathogenesis. This review focuses on aspects that have been most properly addressed and where substantial new information has been gathered include. Topics covered include (a) the identification of T-cell epitopes in gluten and the mechanisms of specific T-cell response in celiac disease small intestine; (b) the mechanisms of induction of mucosal lesion; and (c) the putative role of non-T-cell factors in driving mucosal response to gliadin. After discussing a brief history of the "quest for the cause of celiac disease," we examine the development of the typical celiac lesion (the crypt hyperplastic mucosal atrophy) as it generally unfolds: the increased entry of dietary antigens; the early changes, linked to specific components of the innate immunity rather than to its adaptive branch; the most thoroughly investigated subsequent response, involving a strong T-cell response and cytokines; and the factors responsible for enterocytes' death. The emerging pattern is that of a complex interaction of factors, although far from being completely understood, but fascinating as it opens an incredible window of knowledge on an autoimmune disorder whose environmental factor is known, whose autoantigen is known, whose autoantibodies are known: a truly unique situation in medicine.

Intraepithelial and lamina propria lymphocytes show distinct patterns of apoptosis whereas both populations are active in Fas based cytotoxicity in coeliac disease

BACKGROUND

Lamina propria (LPLs) and intraepithelial (IELs) lymphocytes are markedly increased in coeliac mucosa, and are thought to play a crucial role in the generation of villous atrophy in coeliac disease (CD). However, the mechanisms by which they mediate the killing of enterocytes in this condition are still poorly characterised.

AIM

We investigated Fas mediated cytotoxicity and apoptosis of both LPLs and IELs, isolated from 10 untreated coeliac patients, 10 coeliac patients on a gluten free diet, and 10 biopsied controls.

METHODS

Fas and Fas ligand expression were assessed by flow cytometry and immunocytochemistry. Lymphocyte cytotoxicity against Fas expressing Jurkat cells was determined by the Jam test. The effect of the antagonist ZB4 anti-Fas antibody on apoptotic activity exerted by coeliac lymphocytes against enterocytes was analysed. Lymphocyte apoptosis was assessed by oligonucleosome ELISA.

RESULTS

LPLs and IELs showed increased apoptotic activity and higher levels of Fas ligand expression in untreated CD compared with treated CD patients and controls. Enterocyte apoptosis observed after coculturing coeliac lymphocytes and enterocytes in the presence of ZB4 antibody was reduced. In active CD, LPLs manifested increased apoptosis whereas IELs showed decreased apoptosis.

CONCLUSIONS

Our results support the involvement of the Fas/Fas ligand system in CD associated enterocyte apoptosis. Increased LPL apoptosis is likely to downregulate mucosal inflammation whereas decreased IEL apoptosis could be responsible for autoimmune and malignant complications of CD.

Increased enterocyte apoptosis and Fas-Fas ligand system in celiac disease

Our aim was to evaluate whether increased enterocyte apoptosis was responsible for mucosal flattening in celiac disease (CD), and, since the mechanisms responsible for tissue injury in this condition are unknown, we studied the possibility that the Fas-Fas ligand (FasL) system may be involved. Endoscopic duodenal biopsy specimens from 12 patients with untreated and 12 with treated CD and 12 control subjects were evaluated for enterocyte apoptosis by the terminal deoxynucleotidyl transferase-mediated digoxigenin-deoxyuridine triphosphate nick-end labeling assay and for Fas and FasL expression by immunohistochemistry. A coculture of isolated enterocytes (targets) and purified lamina propria mononuclear cells (LPMCs) (effectors) was performed in the absence or presence of an antagonistic ZB4 anti-Fas antibody. We found a significant correlation between the degree of villous atrophy, morphometrically evaluated, and the level of enterocyte apoptosis, suggesting that mucosal flattening is a consequence of exaggerated epithelial cell death. Most celiac enterocytes express Fas, and LPMCs express FasL. The abolishment of enterocyte apoptosis observed in the presence of ZB4 antibody suggests that enterocytes are potential targets of lymphocyte infiltrate. These results directly demonstrate that FasL-mediated apoptosis is a major mechanism responsible for enterocyte death in CD.