CD66d/CEACAM3

CD66d/CEACAM3 is a granulocyte-restricted member of the CEACAM family, carrying a single IgV-like extracellular domain and a short cytoplasmic tail with an ITAM-like motif. Unlike its relatives, CEACAM3 functions mainly as a pattern-recognition receptor for human-specific pathogens: it directly binds Opa proteins of Neisseria gonorrhoeae and Neisseria meningitidis, and the bound bacteria are engulfed through a Rac-dependent actin-remodeling process driven by its cytoplasmic tail. CD66d therefore represents a dedicated opsonin-independent phagocytic receptor of innate immunity. Its expression is essentially confined to neutrophils, which supports its use in myeloid immunophenotyping.