Fine tuning of the DNAM-1/TIGIT/ligand axis in mucosal T cells and its dysregulation in pediatric inflammatory bowel diseases (IBD).

De-regulated T-cell activation and functions are pivotal in the orchestration of immune-mediated tissue damage in IBD. We investigated the role of DNAM-1 (co-activating)/TIGIT (co-inhibitory)/ligand axis in the regulation of T-cell functions and its involvement in IBD pathogenesis. We show that DNAM-1 and TIGIT display a peculiar expression pattern on gut mucosa T-cell populations, in a microenvironment where their shared ligands (PVR and Nectin-2) are physiologically present. Moreover, DNAM-1 family receptor/ligand system is perturbed in IBD lesions, in a disease activity-dependent manner. The expression profile of CCR6 and CD103 mucosa addressins suggests that microenvironment-associated factors, rather than skewed recruitment of circulating T-cell populations, play a more relevant role in supporting the establishment of DNAM-1 and TIGIT expression pattern in mucosal T-cell populations, and may explain its alteration in IBD. Although both co-receptors mark functionally competent T cells, DNAM-1 and TIGIT segregate on T cells endowed with different proliferative potential. Moreover, their opposing role in regulating T-cell proliferation exquisitely depends on ligand availability. All together, our data propose a role for DNAM-1 and TIGIT in regulating mucosal T-cell activation and immune homeostasis, and highlight the involvement of an imbalance of this system in IBD.

Size and dynamics of mucosal and peripheral IL-17A+ T-cell pools in pediatric age, and their disturbance in celiac disease.

Mucosal interleukin (IL)-17A-producing T cells contribute to protective antimicrobial responses and to epithelial barrier integrity; their role in celiac disease (CD) is debated. We analyzed the frequency and developmental dynamics of mucosal (intraepithelial lymphocytes (IEL)) and circulating (peripheral blood (PB)) IL-17A (T17) and/or interferon (IFN)-γ-producing (T1, T1/T17) T-cell populations in 86 pediatric controls and 116 age-matched CD patients upon phorbol myristate acetate/ionomycin or CD3/CD28 stimulation. T17 and T1/17 are physiologically present among IEL and PB populations, and their frequency is selectively and significantly reduced in CD IEL. The physiological age-dependent increase of Th17 IEL is also absent in CD, while IFN-γ-producing PB-T cells significantly accumulate with patient's age. Finally, the amplitude of IL-17A+ and IFN-γ+ T-cell pools are significantly correlated in different individuals; this relationship only applies to CD4+ T cells in controls, while it involves also the CD4- counterpart in CD patients. In conclusion, both size and dynamics of mucosa-associated and circulating IL-17A+ T-cell pools are finely regulated in human pediatric subjects, and severely disturbed in CD. The impaired IL-17A+ IEL-T pool may negatively impact on epithelial barrier efficiency, and contribute to CD mucosa damage; the disturbed dynamics of circulating IL-17A+ and IFN-γ+ T-cell pools may be involved in the extraintestinal autoimmune manifestations associated with CD.