A major function of NKG2D linking innate and adaptive immunity is to upregulate antigen-specific CTL-mediated cytotoxicity in tissues expressing stress-induced NKG2D ligands, such as MIC, by coactivating TCR signaling. Here, we show that, under conditions of dysregulated IL15 expression in vivo in patients with celiac disease and in vitro in healthy individuals, multiple steps of the NKG2D/DAP10 signaling pathway leading to ERK and JNK activation are coordinately primed to activate direct cytolytic function independent of TCR specificity in effector CD8 T cells. These findings may not only explain previous reports of transformation of CTL into NK-like "lymphokine-activated killers" (LAK cells) under high doses of IL2 (a substitute for IL15) but may also have significant implications for understanding and treating immunopathological diseases.

Celiac disease is an intestinal inflammatory disorder induced by dietary gluten in genetically susceptible individuals. The mechanisms underlying the massive expansion of interferon γ–producing intraepithelial cytotoxic T lymphocytes (CTLs) and the destruction of the epithelial cells lining the small intestine of celiac patients have remained elusive. We report massive oligoclonal expansions of intraepithelial CTLs that exhibit a profound genetic reprogramming of natural killer (NK) functions. These CTLs aberrantly expressed cytolytic NK lineage receptors, such as NKG2C, NKp44, and NKp46, which associate with adaptor molecules bearing immunoreceptor tyrosine-based activation motifs and induce ZAP-70 phosphorylation, cytokine secretion, and proliferation independently of T cell receptor signaling. This NK transformation of CTLs may underlie both the self-perpetuating, gluten-independent tissue damage and the uncontrolled CTL expansion leading to malignant lymphomas in severe forms of celiac disease. Because similar changes were detected in a subset of CTLs from cytomegalovirus-seropositive patients, we suggest that a stepwise transformation of CTLs into NK-like cells may underlie immunopathology in various chronic infectious and inflammatory diseases.

SUMMARY Tissue-resident lymphocytes play a key role in immune surveillance, but it remains unclear how these inherently stable cell populations respond to chronic inflammation. In the setting of celiac disease (CeD), where exposure to dietary antigen can be controlled, gluten-induced inflammation triggered a profound depletion of naturally occurring Vγ4+/Vδ1+ intraepithelial lymphocytes (IELs) with innate cytolytic properties and specificity for the butyrophilin-like (BTNL) molecules BTNL3/BTNL8. Creation of a new niche with reduced expression of BTNL8 and loss of Vγ4+/Vδ1+ IELs was accompanied by the expansion of gluten-sensitive, interferon-γ-producing Vδ1+ IELs bearing T cell receptors (TCRs) with a shared non-germ-line-encoded motif that failed to recognize BTNL3/BTNL8. Exclusion of dietary gluten restored BTNL8 expression but was insufficient to reconstitute the physiological Vγ4+/Vδ1+ subset among TCRγδ+ IELs. Collectively, these data show that chronic inflammation permanently reconfigures the tissue-resident TCRγδ+ IEL compartment in CeD.

Coeliac disease (CeD) is a complex, polygenic inflammatory enteropathy caused by exposure to dietary gluten that selectively occurs in a subset of genetically susceptible HLA-DQ8 and HLA-DQ2 individuals 1 , 2 . The need to develop non-dietary treatments is now widely recognized 3 , but it is hampered by the lack of a pathophysiologically relevant gluten- and HLA-dependent preclinical model. Furthermore, while human studies have led to major advances in our understanding of CeD pathogenesis 4 , direct demonstration of the respective roles of disease-predisposing HLA molecules, and adaptive and innate immunity in the development of tissue damage is missing. To address these unmet needs, we engineered a mouse model that reproduces the dual overexpression of IL-15 in the gut epithelium and the lamina propria (LP) characteristic of active CeD, expresses the predisposing HLA-DQ8 molecule, and develops villous atrophy (VA) upon gluten ingestion. We show that overexpression of IL-15 in both the epithelium and LP is required for the development of VA, demonstrating the location-dependent central role of IL-15 in CeD pathogenesis. Furthermore, our study reveals that CD4 + T cells and HLA-DQ8 are required for VA development, because of their critical role in the licensing of cytotoxic T cells to mediate intestinal epithelial cell (IEC) lysis. Finally, it establishes that IFN-γ and transglutaminase 2 (TG2) are central for tissue destruction. This mouse model, by reflecting the complex interplay between gluten, genetics and the IL-15-driven tissue inflammation, represents a powerful preclinical model for the characterization of cellular circuits critically involved in intestinal tissue damage in CeD, and the identification and testing of new therapeutic strategies.

Celiac disease (CeD), caused by immune reactions to cereal gluten, is treated with gluten -elimination diets. Within hours of gluten exposure, either perorally or extraorally by intradermal injection, treated patients experience gastrointestinal symptoms. To test whether gluten exposure leads to systemic cytokine production time -related to symptoms, series of multiplex cytokine measurements were obtained in CeD patients after gluten challenge. Peptide injection elevated at least 15 plasma cytokines, with IL-2, IL-8, and IL-10 being most prominent (fold-change increase at 4 hours of 272, 11, and 1.2, respectively). IL-2 and IL-8 were the only cytokines elevated at 2 hours, preceding onset of symptoms. After gluten ingestion, IL-2 was the earliest and most prominent cytokine (15-fold change at 4 hours). Supported by studies of patient-derived gluten-specific T cell clones and primary lymphocytes, our observations indicate that gluten-specific CD4+ T cells are rapidly reactivated by antigen -exposure likely causing CeD-associated gastrointestinal symptoms.