CEACAM3 is a granulocyte-specific immunoglobulin-related glycoprotein that functions as a major opsonin-independent phagocytic receptor for human-restricted bacterial pathogens 1. Expressed constitutively on neutrophil surfaces 2, CEACAM3 mediates efficient recognition and elimination of Gram-negative bacteria including Neisseria gonorrhoeae, Haemophilus influenzae, and Moraxella catarrhalis 1. The receptor contains an ITAM-like motif in its cytoplasmic tail that serves as a central signaling hub 3, directly coupling upstream activators and downstream effectors of the small GTPase Rac to coordinate actin cytoskeleton rearrangements essential for bacterial internalization and intracellular destruction 4. CEACAM3 represents one of the fastest-evolving human proteins, reflecting its specialized role in pathogen defense 5. Beyond classical antibacterial functions, CEACAM3 modulates responses to fungal pathogens like Candida albicans and participates in broader neutrophil immunoregulation 6. Clinically, CEACAM3 genetic variants influence respiratory syncytial virus-induced asthma exacerbations; specifically, rs7251960 associates with reduced CEACAM3 expression in subjects experiencing exacerbations 7. CEACAM3-mediated phagocytosis is negatively regulated by protein tyrosine phosphatase PTPRJ and Rac-GTP scavenger Cyri-B, suggesting therapeutic targets for enhancing phagocytic capacity 3.