CD64 (Monocytic Macrophage Marker)

CD64 (FcγRI) is a high‑affinity IgG receptor expressed mainly on macrophages and monocytes and upregulated on activated neutrophils. It is a marker of innate immune activation—particularly neutrophil activation during bacterial infection and sepsis—and of systemic inflammation. Measuring neutrophil CD64 by flow cytometry helps distinguish infectious from noninfectious causes of acute inflammatory responses.

Yes. CD64 (FcγRI) is constitutively and strongly expressed on monocytes and macrophages, where it binds IgG with high affinity and mediates phagocytosis, antibody-dependent cellular cytotoxicity, and immune-complex clearance. Neutrophils have little CD64 at rest but upregulate it with inflammatory cytokines or bacterial infection, so CD64 levels are used clinically as an activation and sepsis marker.

CD64 (FcγRI) on macrophages is a high‑affinity IgG receptor that recognizes and binds opsonized pathogens and immune complexes, promoting phagocytosis and antibody‑dependent cellular phagocytosis. Ligand engagement activates intracellular signaling leading to oxidative burst, cytokine release and enhanced antigen processing/presentation to T cells, contributing to pathogen clearance and inflammation.

The principal marker for circulating monocytes is CD14 (often used with CD16 to define subsets). Tissue macrophages are commonly identified by CD68 (an intracellular lysosomal protein); other widely used markers include CD11b and CD45. Polarization markers include CD80/CD86 for M1 and CD163/CD206 for M2 macrophages. Marker choice depends on species, tissue and method.

CD64 (FcγRI) is a high-affinity Fc gamma receptor for IgG expressed mainly on macrophages, monocytes, dendritic cells and activated neutrophils. It binds IgG-opsonized pathogens to mediate phagocytosis, antigen uptake and presentation, trigger inflammatory cytokine release, and enhance antibody-dependent cellular cytotoxicity. CD64 upregulation on neutrophils is also used clinically as a marker of bacterial infection and systemic inflammation.

Neutrophil CD64 is a sensitive and relatively specific biomarker that rises early in bacterial infection and sepsis, helping distinguish infectious from non-infectious inflammation. It can support diagnosis, guide antibiotic decisions, and monitor response, but should not be used alone; results must be interpreted alongside clinical assessment and other laboratory tests (e.g., cultures, procalcitonin, CRP).