CEACAM1 and colorectal carcinoma: F. nucleatum induced by Fap2 mediates T-cell immunoglobulin and ITIM domain (TIGIT) or promotes the apoptosis of lymphocytes and NK cells by activating carcinoembryonic antigen-related cell adhesion molecules 1 (CEACAM1), and protects CRC cells from the cytotoxic effects of NK cells and T lymphocytes [18,89].