Carcinoembryonic antigen-related cell adhesion molecule 1 controls IL-2-dependent regulatory T-cell induction in...

A dysbalance between effector T cells (Tconv) and regulatory T cells (Tregs) and impaired Treg function can cause autoimmune liver disease. Therefore, it is important to identify molecular mechanisms that control Treg homeostasis. Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1; CD66a) is an immune coreceptor with dichotomous roles in T-cell regulation: its short isoform (CEACAM1S) can activate T cells and induce Tregs, whereas its long isoform (CEACAM1L), containing two intracellular immune receptor tyrosine-based inhibitory motifs, can inhibit activated T-cell function. In the liver, CEACAM1 has antifibrotic effects in models of nonalcoholic steatohepatitis. However, its role in immune-mediated hepatitis is unknown. In the mouse model of concanavalin A-induced CD4⁺ T-cell-dependent liver injury, liver damage was aggravated and persisted in Ceacam1^-/- mice. Concomitantly, we observed hyperexpansion of Tconv, but reduction of interleukin (IL)-2 production and hepatic forkhead box protein P3⁺ (Foxp3⁺ )CD4⁺ Treg numbers. CEACAM1^-/- CD4⁺ T cells showed impaired IL-2-mediated signal transducer and activator of transcription 5 (STAT5) phosphorylation, which correlated with a failure of naïve CEACAM1^-/- CD4⁺ T cells to convert into Tregs in vitro. Furthermore, CEACAM1^-/- Tregs expressed reduced levels of Foxp3, CD25, and B-cell lymphoma 2. Adoptive transfer experiments demonstrated that hepatic Treg expansion and suppressive activity required CEACAM1 expression on both CD4⁺ T cells and Tregs. We identified predominant CEACAM1S expression on hepatic CD4⁺ T cells and Tregs from mice with acute liver injury and expression of both isoforms in liver-derived CD4⁺ T-cell clones from patients with liver injury.

Our data suggest that CEACAM1S expression in CD4⁺ T cells augments IL-2 production and STAT5 phosphorylation leading to enhanced Treg induction and stability, which, ultimately, confers protection from T-cell-mediated liver injury. (Hepatology 2018;68:200-214).