Up‐regulation of small intestinal interleukin‐17 immunity in untreated coeliac disease but not in potential coeliac disease or in type 1 diabetes

A. I. Lahdenperä, V. Hölttä, T. Ruohtula, H. M. Salo, L. Orivuori, M. Westerholm‐Ormio, E. Savilahti, K. Fälth‐Magnusson, L. Högberg, J. Ludvigsson, O. Vaarala

Up-regulation of interleukin (IL)-17 in small intestinal mucosa has been reported in coeliac disease (CD) and in peripheral blood in type 1 diabetes (T1D). We explored mucosal IL-17 immunity in different stages of CD, including transglutaminase antibody (TGA)-positive children with potential CD, children with untreated and gluten-free diet-treated CD and in children with T1D. Immunohistochemistry was used for identification of IL-17 and forkhead box protein 3 (FoxP3)-positive cells and quantitative polymerase chain reaction (qPCR) for IL-17, FoxP3, retinoic acid-related orphan receptor (ROR)c and interferon (IFN)-γ transcripts. IL-1β, IL-6 and IL-17 were studied in supernatants from biopsy cultures. Expression of the apoptotic markers BAX and bcl-2 was evaluated in IL-17-stimulated CaCo-2 cells. The mucosal expression of IL-17 and FoxP3 transcripts were elevated in individuals with untreated CD when compared with the TGA-negative reference children, children with potential CD or gluten-free diet-treated children with CD (P < 0·005 for all IL-17 comparisons and P < 0·01 for all FoxP3 comparisons). The numbers of IL-17-positive cells were higher in lamina propria in children with CD than in children with T1D (P < 0·05). In biopsy specimens from patients with untreated CD, enhanced spontaneous secretion of IL-1β, IL-6 and IL-17 was seen. Activation of anti-apoptotic bcl-2 in IL-17-treated CaCo-2 epithelial cells suggests that IL-17 might be involved in mucosal protection. Up-regulation of IL-17 could, however, serve as a biomarker for the development of villous atrophy and active CD.