High-affinity immunoglobulin gamma Fc receptor I (FcγRI) (FcγRI)

High-affinity immunoglobulin gamma Fc receptor I (FcγRI), also known as CD64, is a 72 kDa transmembrane glycoprotein that serves as the only high-affinity receptor for the Fc portion of monomeric IgG (UniProt: P12314). It is constitutively expressed on monocytes and macrophages and can be strongly induced on neutrophils by pro-inflammatory cytokines like IFN-gamma and G-CSF (PubMed: 20634614). Upon binding to IgG-coated pathogens or immune complexes, FcγRI associates with the signal-transducing gamma chain to initiate phagocytosis, antibody-dependent cellular cytotoxicity (ADCC), and the production of reactive oxygen species. In clinical practice, the upregulation of CD64 on neutrophils is a highly specific biomarker for bacterial infection and sepsis (PubMed: 30134473). Therapeutic strategies involving FcγRI include the development of bispecific antibodies that bridge CD64-expressing effector cells to tumor cells, as well as the engineering of therapeutic antibody Fc regions to optimize binding affinity for enhanced or reduced immune activation (PubMed: 10438450). Additionally, FcγRI plays a role in the clearance of immune complexes, making it a target for modulating autoimmune conditions. Its high affinity for IgG1 and IgG3 makes it a central player in the humoral immune response. Drugs like intravenous immunoglobulin (IVIG) interact with this receptor to modulate systemic inflammation. Research continues into its role as a target for antibody-drug conjugates (ADCs) in myeloid leukemias. Overall, FcγRI is a pivotal link between the innate and adaptive immune systems.

Other names

CD64FCGR1AFCGR1CD64 antigenIgG Fc receptor I

Binding to the Fc region of IgG antibodies, leading to the recruitment of the common gamma chain and subsequent signaling through immunoreceptor tyrosine-based activation motifs (ITAMs) to trigger cellular activation.