CEACAM1, an inhibitory co-receptor in T lymphocytes

A number of reports examining the role of CEACAM1 (Carcinoembryonic Antigen-related Cell Adhesion Molecule 1) in T lymphocytes have defined for it both stimulatory or inhibitory co-receptor functions. Using our unique Ceacaml1-/- mouse model, we previously observed that CEACAM1 is not involved in the development nor in the migration of T cells, but that it exerts a co-inhibitory effect on their activation and proliferation. Here, we report that its loss does not affect the ratios of naive and memory helper or cytotoxic T cells. Moreover, cytotoxic T cells from OT-1:Ceacam1-/- mice, resulting from breeding OT-1 TCR transgenic mice with Ceacam1-/- mice, are hyperproliferative and secrete more interleukin-2 and interferon-7 than their OT-1 counterparts. Finally, studies involving CD2-CCl-L transgenic mice whose T cells overexpress CEACAM1 did not consistently yield the hypoproliferative behaviour expected. Together, these findings suggest that CEACAM1 is an inhibitory co-receptor in T cells