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Celiac.com 06/06/2011 - The interplay among the different immune cells mediating intestinal inflammation in celiac disease is complicated indeed. A subset of T regulatory (Treg) cells that express the Foxp3 protein are present in higher numbers in the intestines of patients with active celiac disease than in healthy controls. Treg cells act to suppress the immune system, providing tolerance to self-antigens. A recent report in the American Journal of Gastroenterology demonstrates that these cells proliferate upon the ingestion of gluten in order to suppress an overactive inflammatory response, but that their suppression is in turn suppressed by interleukin-15. First they confirmed that there is in fact increased expression of Foxp3+ cells in the intestinal mucosa of untreated celiac patients; happily, they write that "no significant differences were noted in the number of Foxp3+ cells in biopsy samples of treated celiac disease in comparison with biopsy samples of non-celiac disease controls." Next, they used an in vitro gliadin challenge system - no celiac patients were harmed during the course of this study! - to see if the increase in this cell population was dependent on gliadin, and it was. T cells are so named because they are made in the thymus; this demonstration that they can originate in the small intestine lamina propria is interesting. Treg cells are generally immunosuppressive, and the Treg cells isolated from celiac guts demonstrated this immunosuppressive ability in vitro. So the researchers wondered: why is there still so much inflammation in untreated celiac disease patients? They found that the cytokine IL-15 could suppress the proliferation of Treg cells, and completely shut down their ability to produce interferon gamma (IFN- Î³ ). This is at least partially because Treg cells from celiac patients turn out to have a significantly higher surface density of receptors for IL-15 than Treg cells from healthy controls, rendering them more sensitive to IL-15's effects. Zanzi et al bolstered their findings by achieving the same results using two independent experimental methods. It is not yet clear how IL-15 impairs the suppressive activity of Treg cells. But these scientists are actively working on it. Source: Am J Gastroenterol advance online publication, 5 April 2011; doi: 10.1038/ajg.2011.80
Celiac.com 05/19/2010 - Enteropathy-associated T cell lymphoma is a serious complication of celiac disease, and a major cause of mortality in untreated celiac disease. One possible trigger for Enteropathy-associated T cell lymphoma development is chronic exposure of intraepithelial lymphocytes (IELs) to strong anti-apoptotic signals, that is, signals that interfere in the normal mortality of the IEL cells. These signals are triggered by IL-15, a cytokine that is over-expressed in the enterocytes of people with celiac disease. However, researchers have not yet fully mapped the signaling pathway by which IL-15 transmits these anti-apoptotic signals. Researchers consider type II refractory celiac disease (RCDII) to be a middle step between celiac disease and enteropathy-associated T cell lymphoma. Eliminating abnormal IELs at the RCDII stage would likely block EATL development. So far, though, scientists have not found successful immunosuppressive and/or chemotherapeutic approaches able to accomplish this, and RCDII outcomes remain very poor. A team of researchers recently set out to map the IL-15–driven survival pathway in human IELs, and to determine whether IL-15 triggered pathway in human intraepithelial lymphocytes represents a possible new target in type II refractory celiac disease and enteropathy-associated T cell lymphoma. The research team was made up of Georgia Malamut, Raja El Machhour, Nicolas Montcuquet, Séverine Martin-Lannerée, Isabelle Dusanter-Fourt, Virginie Verkarre, Jean-Jacques Mention, Gabriel Rahmi, Hiroshi Kiyono, Eric A. Butz, Nicole Brousse, Christophe Cellier, Nadine Cerf-Bensussan, and Bertrand Meresse. The are variously affiliated with INSERM U989, the Université Paris Descartes, Faculté de Médecine René Descartes, the Department of Gastroenterology, AP-HP, Hôpital Européen Georges Pompidou, the Institut Cochin, Université Paris Descartes, CNRS (UMR 8104), INSERM U1016, the Department of Pathology, AP-HP, of the Hôpital Necker-Enfants Malades in Paris, with the Division of Mucosal Immunology, Department of Microbiology and Immunology at the Institute of Medical Science at the University of Tokyo in Japan, and the Inflammation Department of AMGEN Inc., in Seattle, Washington, USA. Their current findings reveal that the survival signals IL-15 directs to freshly isolated human IELs, and to human IEL cell lines derived from celiac disease patients with type II refractory celiac disease, depend on anti-apoptotic factors Bcl-2 and/or Bcl-xL. The signals require IL-15RÎ², Jak3, and STAT5 for proper function, but functioned independently of PI3K, ERK, and STAT3. In support of these findings, the team recorded elevated levels of Bcl-xL, phospho-Jak3, and phospho-STAT5 in IELs from patients with active celiac disease and RCDII. Moreover, by incubating patient duodenal biopsies with a fully humanized human IL-15–specific Ab, the team effectively blocked Jak3 and STAT5 phosphorylation. Also, treatment with IL-15–specific Ab caused IEL cell mortality, and wiped out the massive IEL build-up in mice over-expressing human IL-15 in their gut epithelium. The study marks the first successful mapping of the IL-15–driven survival pathway in human IELs, and demonstrates that IL-15 and its downstream effectors are meaningful therapeutic targets in RCDII. These findings will likely help to pave the way for the development of successful immunosuppressive and/or chemotherapeutic treatments that destroy abnormal IELs at the RCDII stage and help to block EATL development, improving outcomes for RCDII patients. Source: Journal of Clinical Investigation doi:10.1172/JCI41344
Celiac.com 03/10/2010 - A team of researchers recently observed that monocytes differentiated with IL-15 support Th17 and Th1 responses to wheat gliadin. They discuss the implications of this discovery for celiac disease in a recent article in Clinical Immunology. The research team included K. M. Harris, A. Fasano, and D. L. Mann of the Pathology Department at the University of Maryland School of Medicine. It is understood that interleukin (IL)-15 contributes to the immuno-pathogenesis of celiac disease. However, the effect of IL-15 on APC that shape adaptive immune responses to gliadin is not well understood. Using PBMC from healthy individuals, the team demonstrated that monocytes differentiated with IL-15 (IL15-DC) produced IL-1beta, IL-6, IL-15, IL-23, TNFalpha and CCL20 in response to pepsin-trypsin digested gliadin (PTG) and activated contact-dependent Th17 and Th1 responses from autologous CD4(+) T cells. Compared with control subjects, PBMC from celiac disease patients showed lower concentrations of IL-15 augmented IFNgamma responses to PTG. So, by generating IL15-DC, IL-15 supports Th17 and Th1 responses to a dietary antigen that produces no such responses in healthy individuals.The team notes that IL-15 hypersensitivity may cause these potentially pathogenic immune responses to develop in celiac patients, but not in healthy individuals. They conclude that the pathogenesis of celiac disease is likely due in part to genetic and/or environmental factors that control IL-15 expression and responsiveness in the gut. Source: Clin Immunol. 2010 Feb 10.