CHANGES in DUODENAL INNATE LYMPHOCYTE SUBSETS INDICATE a SHIFT TOWARDS a PRO-INFLAMMATORY STATE in CELIAC DISEASE

Innate lymphoid cells (ILCs) comprise distinct subsets of immune cells with unique functions. Although alterations in the frequencies of certain ILCs have been reported in inflammatory diseases, including Crohn's disease, their roles in celiac disease (CD) pathogenesis have not been adequately explored. Hence, we investigated the frequency, phenotype and transcription factor and cytokine profiles of ILC populations in patients with newly diagnosed or active celiac disease (ACD) and those on a gluten-free diet (GFD).

Intraepithelial lymphocyte fractions isolated from proximal small intestinal (duodenal) biopsies from ACD (n=7) and GFD (n=9) patients and normal controls (n=11), were analyzed. Lineage-negative (Lin-) CD103⁺ cells comprised two ILC1 populations, NKp44⁺CD56⁺ and NKP44^-CD56^-. The percentage and absolute numbers of NKp44⁺CD56⁺ ILCs were significantly reduced in ACD (%: 4.5±2.7, p<0.0001; abs#: 466±198, p<0.001) and GFD (%: 7.2±2.2, p<0.0001; abs#: 2239±1482, p<0.02) compared to controls (%: 49.9±6.3; abs#: 11608±2987). On the contrary, NKP44^-CD56^- ILCs were increased in ACD (%: 63.6±4.0, p<0.0001; abs#: 8360±2485, p=0.08) and GFD (%: 33.8±3.8, p=0.025; abs#: 5877±1875, p=0.29) compared to controls (%: 19.4±4.0; abs#: 4180±941). Upon in vitro stimulation with PMA and ionomycin, NKp44⁺CD56⁺ ILCs did not secrete IFN-γ, IL-17, IL-22 or IL-5 and they lacked expression of ILC subset-specifying transcription factors. In contrast, NKP44^-CD56^-ILCs expressed T-bet and a significant fraction (34.18± 6.6%) produced IFN-γ.

Our findings indicate heterogeneity within the ILC1 subset in the duodenal epithelium. The observed changes in ILC composition, especially an increase in the NKp44^-CD56^- ILC1 population, suggest that ILCs may contribute to the ongoing inflammation in CD.