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.