CEACAM3 (Carcinoembryonic Antigen-Related Cell Adhesion Molecule 3) is a transmembrane glycoprotein predominantly expressed on human granulocytes, particularly neutrophils. It belongs to the CEACAM family, which plays roles in cell adhesion, immune regulation, and pathogen recognition. CEACAM3 features an extracellular immunoglobulin-variable-like domain, a transmembrane region, and a cytoplasmic tail containing an immunoreceptor tyrosine-based activation motif (ITAM). Unlike other CEACAM members, CEACAM3 is primarily involved in innate immunity, acting as a pathogen receptor that directly binds bacterial pathogens like *Neisseria* species and *Moraxella catarrhalis*. Upon ligand binding, CEACAM3 triggers rapid phagocytosis and oxidative burst via Syk kinase signaling, aiding in bacterial clearance.
Antibodies targeting CEACAM3 are critical tools for studying its function in neutrophil-mediated immunity and inflammatory responses. They are used in immunoassays, flow cytometry, and immunohistochemistry to localize CEACAM3 expression or modulate its activity in experimental models. Dysregulation of CEACAM3 has been implicated in chronic inflammatory diseases and susceptibility to infections. Therapeutic antibodies are also being explored to enhance bacterial clearance or dampen excessive inflammation. However, research remains focused on elucidating its precise interactions with pathogens and signaling pathways, highlighting CEACAM3's potential as a target for immune modulation.