Interleukin-15-Dependent T-Cell-like Innate Intraepithelial Lymphocytes Develop in the Intestine and Transform into Lymphomas in Celiac Disease.

The nature of gut intraepithelial lymphocytes (IELs) lacking antigen receptors remains controversial. Herein we showed that, in humans and in mice, innate intestinal IELs expressing intracellular CD3 (iCD3(+)) differentiate along an Id2 transcription factor (TF)-independent pathway in response to TF NOTCH1, interleukin-15 (IL-15), and Granzyme B signals. In NOTCH1-activated human hematopoietic precursors, IL-15 induced Granzyme B, which cleaved NOTCH1 into a peptide lacking transcriptional activity. As a result, NOTCH1 target genes indispensable for T cell differentiation were silenced and precursors were reprogrammed into innate cells with T cell marks including intracellular CD3 and T cell rearrangements. In the intraepithelial lymphoma complicating celiac disease, iCD3(+) innate IELs acquired gain-of-function mutations in Janus kinase 1 or Signal transducer and activator of transcription 3, which enhanced their response to IL-15. Overall we characterized gut T cell-like innate IELs, deciphered their pathway of differentiation and showed their malignant transformation in celiac disease.

Interleukin 15 and CD4⁺ T cells cooperate to promote small intestinal enteropathy in response to dietary antigen.

BACKGROUND & AIMS: CD4(+) T cells specific for dietary gluten and interleukin 15 (IL15) contribute to the pathogenesis of celiac disease. We investigated whether and how they interact to damage the intestine using mice that overexpress human IL15 in the intestinal epithelium and have CD4(+) T cells specific for ovalbumin, a dietary antigen. METHODS: We crossed mice with CD4(+) T cells specific for ovalbumin (OTII) with mice that overexpress human IL15 under an intestine-specific promoter (B6 × IL15Tge). The offspring (OTII × IL15Tge mice) received control or ovalbumin-containing diets until 3 months of age. Enteropathy was monitored by weight, ratio of villous:crypt length, and the number of intestinal lymphocytes. Phenotype, cytokine production, and degranulation of mucosal and spleen lymphocytes were analyzed by multicolor flow cytometry or enzyme-linked immunosorbent assay. Regulatory T-cell function and CD8(+) T-cell activation were analyzed in co-culture assays. RESULTS: Exposure to ovalbumin reduced growth and led to enteropathy in OTII × IL15Tge mice but not in control OTII × B6 littermates. Enteropathy was associated with expansion of mucosal granzyme B(+) CD8(+) T cells, and developed despite increased frequency of functional ovalbumin-specific regulatory T cells. Ovalbumin-activated CD4(+) T cells secreted IL2, which along with IL15 stimulated expansion of noncognate intestinal cytotoxic CD8(+) T cells, which did not respond to regulatory T cells and induced epithelial damage. CONCLUSIONS: We observed that in mice given food antigen, cooperation between IL15 and CD4(+) T cells is necessary and sufficient to activate CD8(+) T cells and damage the small intestine. We propose that this process is involved in the development of celiac disease.

Activation of the receptor NKG2D leads to production of Th17 cytokines in CD4+ T cells of patients with Crohn's disease.

BACKGROUND & AIMS: The natural killer group 2 member D (NKG2D) is a stimulatory receptor expressed on a subset of mucosal and peripheral CD4+ T cells in patients with Crohn's disease (CD) and other inflammatory diseases. Ligand activation of NKG2D in patients induces CD4+ T cells to release T-helper (Th) 1 cytokines and become cytotoxic. We investigated the Th17 cytokines produced by T cells that express NKG2D in blood and intestinal mucosa samples from patients with CD. METHODS: We isolated CD4+ T cells from peripheral blood and lamina propria samples of patients with CD or ulcerative colitis (UC) and healthy individuals (controls). We analyzed the phenotype and functions of the CD4+NKG2D+ T cells and the cytokines they produce in response to NKG2D stimulation. RESULTS: In patients with CD, CD4+ T cells that express NKG2D produced high levels of interleukin (IL)-17 and IL-22 and expressed high levels of CCR6, the IL-23 receptor, CD161, and RORC (a transcription factor that regulates expression of Th17 cytokines). CD4+ T cells that produced IL-17 expressed high levels of NKG2D and CD161. Costimulation of NKG2D and the T-cell receptor (TCR) significantly increased production of IL-17 and tumor necrosis factor α by CD4+ T cells, compared with activation of only the TCR. CD4+NKG2D+ T cells also responded to Th17 polarization. CONCLUSIONS: NKG2D is a functional marker of CD4+ T cells that produce IL-17 in patients with CD, via costimulation of the TCR and NKG2D. Reagents developed to block NKG2D might reduce gastrointestinal inflammation in patients with CD.