Advances in the Immunogenetics of Coeliac Disease. Clues for ...

Advances in the Immunogenetics of Coeliac Disease. Clues for Understanding the Pathogenesis and Disease Heterogeneity ˜ A, J. A. GARROTE & J. B. A. CRUSIUS A. S. PEN Dept. of Gastroenterology and Hepatology, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain, Dept. of Gastroenterology, Gastrointestinal Immunology, Vrije Universiteit, Amsterdam, The Netherlands, and Paediatrics and Immunologic Laboratory, Valladolid, Spain

Scand J Gastroenterol Downloaded from informahealthcare.com by Vrije Universiteit Amsterdam on 04/18/12 For personal use only.

Penã AS, Garrote JA, Crusius JBA. Advances in the immunogenetics of coeliac disease. Clues for understanding the pathogenesis and disease heterogeneity. Scand J Gastroenterol 1998;33 Suppl 225:56–8. Recent studies using the technique of the human genome screening in families with multiple siblings suffering from coeliac disease have suggested the presence of at least four different chromosomes in the predisposition to suffer from coeliac disease. Two loci in chromosome 6 appear to be important in disease susceptibility. Other studies based on cytokine gene polymorphisms have found a strong association with a particular haplotype in the TNF locus. This haplotype carries a gene for a high secretor phenotype of TNFa. The finding may be important in understanding the heterogeneity of inflammatory response. Evidence has been presented in favour of a predominantly Th1 pattern of cytokine production by the coeliac disease associated HLA-DQ restricted T cell clones. HLA-DQ2 and -DQ8 restricted gliadinspecific T cells have been shown to produce IFN-g, which appears to be an indispensable cytokine in the damage to enterocytes encountered in the small intestine, since the histological changes can be blocked by anti-IFN-g antibodies in vitro. TNF-a, also produced by several T cell clones, may in conjunction with IFN-g have a toxic effect or enhance the IFN-g-induced increase of HLA-class II expression on surface enterocytes. In the lamina propria this leads to an increased expression of adhesion molecules such as ICAM-1 on T lymphocytes and macrophages. Th1 cells also activate cytotoxic CD8 T cells that migrate in the epithelial layer, and stimulate further LPL macrophages to produce IFN-g and TNF-a enhancing the inflammatory response. During this process autoreactive T cells proliferate, creating a situation which is very similar to the process that takes place in autoimmune diseases. Occasionally, this inflammatory destruction of the small intestinal integrity initiated by gluten peptides goes further and develops into a proper autoimmune disease which requires the use of immunosuppressive drugs in addition to a gluten-free diet. Key words: Coeliac disease; genetics; MHC; TNF A. S. Penã, Servicio Patologıá Digestiva, Hospital de la Santa Creu i Sant Pau, Sant Antoni Marıá Claret, 167, 08025 Barcelona, Spain (fax: 34 3 291 9278)

Recent studies in Italy and Sweden have demonstrated that coeliac disease has a greater prevalence than originally believed, with figures from 1:200 to 1:300 in the general asymptomatic population (1–3). There are also groups with an increased risk of suffering from this disease, such as the patients with autoimmune diseases. Diabetes mellitis (4), hypothyroidism, Sjo¨gren syndrome, Addison disease, vasculitis, lupus erythematosus (5), persons with Down syndrome (6), patients with osteopenia (7) or relatives of patients with coeliac disease (8). The classical triad of steatorrhoea, weight loss and anaemia is less common than we thought and the patients often consult other specialists of internal medicine, such as the haematologist, the immunologist or the endocrinologist before the gastroenterologist. Fortunately, the wide use of serological screening with antiendomysium, antigliadin and antireticulin as well as the relative easiness of obtaining duodenal biopsies has simplified the diagnosis (9, 10).

GENETIC BASIS OF COELIAC DISEASE Although the first-established association was made with class I molecules of the HLA system (HLA-B8) and with class II molecules (HLA-DR3 in northern Europe HLADR5/-DR7 in the south), the common base is the association with the HLA-DQ2 (11). HLA-DQ2 is present in 90 to 95% of the patients with coeliac disease and in 20 to 30% of the healthy European control group. Coeliac disease is primarily associated with the combination of two HLA-DQ alleles, the HLA-DQA1*0501 and the HLA-DQB1*02, arranged either in a cis or trans configuration in the majority of patients, whereas a minority carry the HLA-DR4 associated DQB1*0302, serologically known as HLA-DQ8 antigen. In spite of the very close association between the HLA system and coeliac disease, other genes within chromosome 6, such as the TNF genes (12), may influence the severity of the disease (Fig. 1).

Immunogenetics of Coeliac Disease

57


Fig. 1. Short arm of chromosome 6 Map of the MHC.

Tumour necrosis factor alpha (TNF alpha), lymphotoxin alpha (TNF beta), and interleukin-1 receptor antagonist (IL1ra) have been investigated. These cytokines are small polypeptides important in regulating proliferation, differentiation, and function of cells. They function as chemical messengers between cells of the immune, inflammatory and other systems and are therefore important in immune response, inflammation, and fibrosis. A balance between levels of cytokines, their receptors, and inhibitors controls inflammatory reactions. Using molecular typing techniques we have recently studied 4 polymorphisms at the TNFa/LTa locus. Bi-allelic polymorphisms in these loci are arranged in haplotypes and we established that 5 TNF haplotypes are present in the Dutch population (Fig. 2). We have found that in patients with coeliac disease, haplotype TNF-E is increased (P = 0.0001) (Fig. 3). Although large inter-individual differences in intrinsic capacity to produce TNFa and LTa exist, it seems that differences in secretion are related to polymorphisms in the TNF region. Position-308 (TNF-E) plays an important role in the regulation of TNFa secretion. Since the ‘high secretor’ haplotype TNF-E is significantly associated with coeliac disease we have postulated that this may represent the genetic basis for the chronic inflammatory response in the small-bowel tissue of CD patients. Studies to verify this hypothesis are under way. Haplotype TNF-E may be related to severity or other clinical characteristics of CD. Recent studies using the molecular biology technology of chromosome-wide screening the genes of the entire genome in coeliac concordant families have confirmed the involvement of various chromosomes in the predisposition to the disease (13). In this study, performed in families in the western counties of Ireland, it was found that in chromosome

Fig. 3. Frequencies of TNF haplotypes in coeliac disease patients and controls.

6 there was another locus outside the HLA region that was important in defining the susceptibility. There were other regions of possible influence in chromosome 11p, 7q, and chromosome 22 near the centromere. TOLERANCE INDUCTION To respond to the immunologic basis of coeliac disease it is necessary to consider the mucosal immunity and the phenomena known as tolerance. The antigens that are orally introduced to the organism induce a local immunological response or a state of non-response or tolerance. In the latter case, if a reminder dose of the antigen is given parenterally, no immunological response is produced. This lack of specific response to gliadin affects both the formation of antibodies and the cellular immunity. This phenomenon, which could not be completely clarified, is accompanied by the activation of a subgroup of T cells. These cells produce IL-4, -5, -6, -9, -10, and 13 (response type 2 or Th2/Th3), which together with the TGFb stimulate the formation of IgA and maintain the integrity of the epithelial barrier. At the same time this type 2 response induces the suppression of T cells with type 1 response (Th1), which would favour the production of IgM and IgG and the delayed type hypersensitivity (DTH) (14). In the mucosa the prime naive T cell response (Th0) when activated by small quantities of antigens normally are predominantly of type 2 (Th2 and Th3), probably due to the interactions with the B cells, which are very abundant in these tissues. In the following contacts with the antigen, the secondary response will still be of type 2, whichever the entry site is. Moreover, the Peyer’s patches, the complex antigen-antibody of class IgA and the liver, which receives the blood from the portal vein, contribute to favour immunological suppression (15). IMMUNOLOGICAL BASIS OF COELIAC DISEASE

Fig. 2. The four polymorphims are inherited as five haplotypes.

When the immune response is insufficient or non-existent,


58

A. S. Penã et al.

diseases are produced which are characterized by a humoral and/or cellular response to defend the individual against external agents. When, on the contrary, there is an over response, with the formation of abnormal proteins or without, the immune-proliferated disease is produced. Other times, the immune response is directed to the very elements of the individual, based on autoimmune phenomena. More often, in the digestive tract there are various diseases with an immune dysregulation, in which it is not yet known if the immunological phenomena are just partners or if they are involved in the pathogenesis. When there is an immediate response with IgE production, activation of mast cells and basophils, allergic diseases are produced. The strong association which exists between coeliac disease and the major system of the antigens for histocompatibility, the HLA system explains in greater part the genetic base of this disease, the immunological changes and the association to autoimmune diseases. These heterodimeric molecules play a crucial role in the presentation of processed peptide antigens to CD4 T cells. Associations with alleles at the closely linked HLA-DRB1 locus are thought to be secondary to those with the DQ loci. Studies among several ethnic patient groups failed to provide conclusive evidence for independent associations with polymorphisms in the major histocompatibility complex (MHC) class II genes centromeric to the HLA-DQ locus (e.g. TAP2, HLA-DP). Nor have studies provided evidence for independent associations with genes of the adjacent (non-HLA) MHC class III region (e.g. Bf, C2, C4 and HSP70). However, these and more telomerically located much less polymorphic MHC class III genes encode factors that modulate the immune response and may determine the clinical heterogeneity of the disease. It is possible that the variants of these genes play a different modulatory role in the control of inflammation. It may thus be that the combination of alleles at the primary disease associated HLA-DQ loci and at other non-HLA genes determine the clinical outcome of the disease. Short-chain toxic peptides produced by the ingestion of gluten (gliadin and related prolamines) are bound to HLA-class II molecules in the late endosomal or lysosomal compartment of enterocytes during uptake across the small intestinal epithelium. This is an early event characterized by HLA-DR over expression in the villus enterocytes. Antigen presenting cells in the lamina propria cells present digested peptides to antigen-specific CD4 T cells. It is interesting that the T cells, which carry these specific DQ2 molecules on the surface, are capable of responding to gliadin peptides, which would suggest they are involved in the abnormal immunological response (16, 17). Some patients with negative HLA-DQ2 have inherited other genes, apparently also very specific, the HLA-DR4 and the HLA-DQ8+. Isolated intestinal T cells that are HLA-DR4+ respond to the gliadin peptides when presented in the context of DQ8 molecules (18).

COELIAC DISEASE A POLYGENIC AND MULTIFACTORIAL DISEASE Coeliac disease is an enteropathy characterized by intolerance to gluten in individuals who are genetically predisposed to the disease. However, its aetiology is multifactorial and requires the addition of environmental factors (infections, dietary habits, and age of introduction to the gluten) to the genetic predisposition. The intestinal lesion is immunologically mediated, being gliadin the trigger of a series of not yet fully clarified chain reactions which produce an activation of the immune system, and results in the flattening of the intestinal mucosa and in a hyperplasia of the crypts.

REFERENCES 1. Stenhammar L. Childhood coeliac disease in Sweden [Letter; comment]. Lancet 1994;344:341–2. 2. Catassi C, Ratsch IM, Fabiani E, et al. Coeliac disease in the year 2000: exploring the iceberg [see Comments]. Lancet 1994;343:200–3. 3. Ascher H, Kristiansson B. Childhood coeliac disease in Sweden [Letter; comment]. Lancet 1994;344:340–1. 4. Maki M, Hallstrom O, Huupponen T, Vesikari T, Visakorpi J. Increase prevalence of coeliac disease in diabetes. Arch Dis Child 1984;59:739. 5. Penã AS, Crusius JBA. Malignancy, autoimmune disease, survival and quality of life in coeliac disease. Pedia´trika 1996; 16:406–11. 6. Dias JA, Walker-Smith J. Down’s syndrome and coeliac disease [see Comments]. J Pediatr Gastroenterol Nutr 1990;10:41–3. 7. Pistorius LR, Sweidan WH, Purdie DW, et al. Coeliac disease and bone mineral density in adult female patients. Gut 1995;37: 639–42. 8. Vazquez H, Sugai E, Pedreira S, et al. Screening for asymptomatic coeliac sprue in families. J Clin Gastroenterol 1995;21:130–3. 9. Blanco-Quiro´s A, Arranz E. Humoral immunity in coeliac disease. Pedia´trika 1996;16:363–6. 10. Von Blomberg BME, Mearin ML, Houwen RHJ, Penã AS. Serological assays for diagnosing coeliac disease. Pedia´trika 1996;16:367–71. 11. Lundin KE, Gjertsen HA, Scott H, Sollid LM, Thorsby E. Function of DQ2 and DQ8 as HLA susceptibility molecules in coeliac disease. Hum Immunol 1994;41:24–7. 12. Crusius JBA, Mulder CJJ, Mearin ML, Penã AS. Polymorphisms in non-HLA genes: contribution to coeliac disease. Pedia´trika 1996;16:399–405. 13. Zhong F, McCombs CC, Olson JM, et al. An autosomal screen for genes that predispose to coeliac disease in western countries of Ireland. Nat Genet 1996;14:329–33. 14. Mosmann TR, Sad S. The expanding universe of T-cell subsets: Th1, Th2 and more. Immunol Today 1996;17:138–46. 15. Kleinman RE, Harmatz PR, Walker WA. The liver: an integral part of the enteric mucosal immune system. Hepatology 1982;2: 379–84. 16. Jensen K, Sollid LM, Scott H, et al. Gliadin-specific T cell responses in peripheral blood of healthy individuals involve T cells restricted by the coeliac disease associated DQ2 heterodimer. Scand J Immunol 1995;42:166–70. 17. van de Wal Y, Kooy YMC, Drijfhout JW, Amons R, Koning F. Peptide binding characteristics of the coeliac disease-associated DQ(alpha1*0501, beta1*0201) molecule. Immunogenetics 1996;44:246–53. 18. Lundin KEA, Scott H, Fausa O, Thorsby E, Sollid LM. T-cells from the small intestinal mucosa of a DR4,DQ7/DR4,DQ8 coeliac disease patient preferentially recognize gliadin when presented by DQ8. Hum Immunol 1994;41:285–91.