CD64. also known as Fcγ receptor I (FcγRI), is a high-affinity receptor for the Fc portion of immunoglobulin G (IgG). It belongs to the immunoglobulin superfamily and is encoded by the FCGR1A gene in humans. Structurally, CD64 is a transmembrane glycoprotein composed of three extracellular immunoglobulin-like domains. Unlike low-affinity Fcγ receptors (CD32 and CD16), CD64 binds monomeric IgG with high specificity, playing a critical role in antibody-mediated immune responses.
CD64 is constitutively expressed on myeloid cells, including monocytes, macrophages, and dendritic cells, but its expression can be upregulated by inflammatory cytokines like interferon-gamma (IFN-γ). This receptor facilitates phagocytosis, immune complex clearance, and antibody-dependent cellular cytotoxicity (ADCC). Its activation also triggers pro-inflammatory signaling pathways, enhancing antigen presentation and cytokine release. Due to its restricted expression pattern and responsiveness to inflammation, CD64 serves as a biomarker for immune activation. For instance, elevated CD64 levels on neutrophils are clinically associated with bacterial infections and sepsis, aiding in differential diagnosis.
CD64-specific antibodies are widely used in research and diagnostics. They enable immune cell profiling via flow cytometry and help study receptor-ligand interactions. Therapeutic applications include targeting CD64 for drug delivery or modulating immune responses in autoimmune diseases. However, its role in certain pathologies, such as chronic inflammation or cancer, remains under investigation. Overall, CD64 bridges innate and adaptive immunity, making it a focal point in immunology and translational medicine.