CD5-mediated mTOR inhibition on T cells through binding of soluble CEACAM1

Introduction Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) controls immunity via self- or heteroligation. Its soluble isoform (sCC1) is elevated in sera of patients with obstructive and autoimmune liver diseases. In ConA-mediated hepatitis, Ceacam1-/- mice show exacerbation and persistence of hepatitis as a result of impaired Treg function and stability. T cell activation and Treg induction use the short CEACAM1 isoform (CECAM1-S), whereas its ITIM-bearing long isoform (CEACAM1-L) is required to impose T cell inhibition. Recently, we identified the Treg regulator CD5 as a novel binding partner for sCC1.