Abnormal apical-to-basal transport of dietary ovalbumin by secretory IgA stimulates a mucosal Th1 response

Celiac disease in children

Celiac disease is an autoimmune enteropathy, triggered by ingestion of gluten in genetically predisposed individuals. Since the use of anti-transglutaminase and anti-endomysium antibodies in the early 1990s, two main groups of clinical presentation can be identified: patients with a symptomatic form of the disease, and patients with a pauci (a)-symptomatic form detected during the work-up of another autoimmune disease or due to a family history of celiac disease. The prevalence of both forms of the disease is currently estimated between 1/100 and 1/400. Classical form of the disease is characterized by occurrence of diarrhoea, failure to thrive, and abdominal bloating in young infants in the months following gluten introduction. Serological tests show high level of anti-transglutaminase and anti-endomysium antibodies. Until recently, the diagnosis required duodenal biopsies that show villous atrophy. HLA genotype can help for diagnosis: the absence of the HLA-DQ2 or DQ8 alleles has a high negative predictive value. European guidelines recently proposed to reconsider the need for systematic endoscopy in typical symptomatic forms with high level of anti-transglutaminase and positive anti-endomysium. These recommendations are being assessed now. Currently, the gluten-free diet remains the only effective treatment for celiac disease. Children with celiac disease have to exclude from their diet all products containing wheat, barley and rye. Gluten-free diet causes clinical remission within a few weeks, but normalization of the small bowel mucosa and negativity of anti-transglutaminase antibodies are obtained in several months or even years. Gluten-free diet is useful to obtain clinical assessment, but also to prevent long-term complications of celiac disease, mainly osteoporosis, other autoimmune diseases, decreased fertility and cancers.

Interleukin-15, a master piece in the immunological jigsaw of celiac disease

BACKGROUND

The immune response causing celiac disease (CD) depends on the activation of intestinal CD4+ T cells by gluten-derived peptides presented by HLA-DQ2 or HLA-DQ8 molecules, the main genetic risk factor. However, additional factors are necessary to impair immune tolerance to dietary gluten, to stimulate intraepithelial lymphocytes (IEL) and to induce intestinal damage.

KEY MESSAGES

Current data point to a central role of interleukin-15 (IL-15). In situ and ex vivo studies indicate that IL-15 stimulates the accumulation and cytotoxic activation of CD8+ T IEL in active CD, and that of the malignant innate-like IEL in type II refractory CD (RCDII). Other studies show that IL-15 impairs the immunoregulatory control of effector T cells, notably CD8+. Recently, animal models have been designed to investigate the respective role of CD4+ T cells and IL-15 in CD. We discuss more particularly our results in such a model, which shows that IL-15 produced in excess in the intestine can cooperate with CD4+ T cells specific for a dietary antigen to trigger a celiac-like enteropathy. In this mouse model, CD4+ T cells activated by dietary ovalbumin secreted IL-2 which, along with IL-15, stimulated the expansion of noncognate intestinal cytotoxic CD8+ T cells containing large amounts of granzyme B. In the presence of IL-15, the latter cells did not respond to regulatory T cells, and accumulated in the intestine close to epithelial damage.

CONCLUSION

On the basis of these data, we propose that, in CD, gluten-specific CD4+ T cells synthesize cytokines that synergize with IL-15 to license the expansion and activation of cytotoxic IEL, which drive tissue damage. We suggest that IL-15 is a meaningful therapeutic target, notably in patients with RCDII in which malignant IEL can respond to IL-15 independently of signals provided by CD4+ T cells.

Lessons from rodent models in celiac disease

Over the past 25 years, studies led in humans have considerably improved our understanding of celiac disease, a complex disease that is generally defined as an autoimmune-like enteropathy induced by dietary gluten in genetically predisposed individuals. Recently, large efforts were also invested in the development of mouse models in order to explore pathogenic hypotheses, and also with the goal to design pretherapeutic models that could be used to test innovative therapies. Yet, modeling this complex multifactorial disease has been a very challenging task. Herein, we review how approaches in rodents have provided insight into celiac disease pathophysiology and also highlight the difficulties met to fully recapitulate the human disease.