Phenotypic shift of small intestinal intra-epithelial type 1 innate lymphoid cells in celiac disease is associated with enhanced cytotoxic potential

Abstract

The small intestinal (SI) epithelium harbors a heterogeneous population of lymphocytes that mediate mucosal damage and repair in celiac disease (CD). The composition and roles of human proximal SI intra-epithelial innate lymphoid cells (ILCs), and their alterations in CD, are not well understood. We report that duodenal intra-epithelial ILCs predominantly consist of natural killer (NK)p44 + CD127 − cytotoxic ILC1s and NKp44 − CD127 + helper ILC1s, while ILC3s only represent a minor population. In patients with newly diagnosed or active CD (ACD) and refractory CD type 1 (RCD I), the frequency of SI NKp44 + ILCs is decreased, with restoration of NKp44 + ILC frequency observed in patients adhering to a gluten-free diet who show evidence of mucosal healing. Moreover, the frequency of SI NKp44 − ILCs is increased in ACD and RCD I patients and correlates with the severity of villous atrophy and epithelial damage, as assessed by serum levels of fatty acid binding protein 2 (FABP2). We show that the ILC alterations in CD represent a phenotypic shift of cytotoxic ILC1s rather than an increase in helper ILC1s or transdifferentiation of ILC1s to ILC3s, and activation-induced loss of NKp44 by cytotoxic ILC1s is associated with increased interferon (IFN)-γ expression and release of lytic granules. These findings suggest that intra-epithelial NKp44 − CD127 − cytotoxic ILC1s may contribute to mucosal damage in CD.

Innate Lymphoid Cells and Celiac Disease: Current Perspective

“…In contrast to the down-regulation of NKp44 in functionally exhausted NK cells, 116,117 elevations in NKp44 -ILC1s in CD correlated with increased severity of villous atrophy and enterocyte damage and they produced higher amounts of IFN-g and cytotoxic granule proteins. 77 An increase in small intestinal lamina propria TNF-a-and IFN-g-producing ILCs, likely representing ILC3s and possibly a proportion of helper ILC1s, has also been reported in active CD. 118 Because TNFa has been shown to contribute to increased intestinal permeability, 119 these ILCs may facilitate the transfer of luminal antigens to APCs in the lamina propria.…”

“…72 CD103 þ , CD127 -, NKp44 þ ieILC1s, and CD127helper ILC1s represent the major non-NK cell ILC subsets within the small intestinal epithelium, while CD127 þ ILC3s account for only a minor component. 66,77 An increase in lamina propria helper ILC1s, however, has been observed in active Crohn's disease. 78 Both tissue-resident NK cells and ILC1s are the main sources of IFN-g required for early defense against intracellular pathogens such as Toxoplasma gondii 56,79 and Salmonella typhimurium.…”

“…In newly diagnosed or active CD, TCR þ IELs expand to a greater degree than CD7 (bright)þ iCD3ε þ /sCD3innate IELs, which comprise predominantly ieILC1s and helper ILC1s. 77,105,111,112 In addition to stimulating T-IELs, IL15 also induces the proliferation and enhanced survival of iCD3 þ ILC1-like innate IELs in CD. 66,75,113,114 On the other hand, NKp44 and NKp46-double positive NK cells are decreased in the small intestinal epithelium in active CD.…”

Innate Lymphoid Cells as Regulators of Epithelial Integrity: Therapeutic Implications for Inflammatory Bowel Diseases

“…With an increasing number of intestinal ILC1s in CD ( 17 , 44 ), their TGF-β1-mediated beneficial effect on crypt stem cells ( 45 ) might contribute to the resolution of intestinal inflammation by promoting the reconstruction of an intact epithelial barrier. In contrast, via the secretion of IFN-γ, ILC1s were suggested to additionally have a negative influence on tight junctions ( 54 , 79 , 80 ), implying functional subgroups of ILC1s. Despite their overall low number in the healthy and inflamed intestine, ILC2s could be demonstrated to favor mucosal healing and disease control on the level of enterocytes, goblet cells, tuft cells and crypt stem cells by secreting AREG and IL-13 ( 69 , 71 , 84 ).…”

“…Deletion of intraepithelial ILC1s with an anti-NK1.1 antibody was associated with reduced epithelial disruption and a diminished accumulation of inflammatory cells ( 54 ), proposing a negative influence of ILC1s on colitis-associated barrier destruction. In the context of celiac disease, increased percentages of intraepithelial NKp44 − cytotoxic ILC1s have been reported in the human small intestine, which significantly correlated with an increased IFN-γ production as well as an increased disease severity and epithelial breakdown ( 79 ). In addition, enhanced levels of ILC1- and ILC3-derived IFN-γ and TNF-α upon simian immunodeficiency virus infection in rhesus macaques associated with an increased loss of colonic tight junctions, resulting in epithelial instability and increased microbial translocation ( 80 ), supporting a detrimental functional role of ILC1s on the maintenance of an intact epithelial gut barrier ( Figure 2 ).…”