Fc γ RI, also known as CD64, is an integral cell membrane glycoprotein that transmits activation signals through the associated Fc R γ chain, commonly referred to as Fc-γ receptor 1 (Fc γ RI), and the high affinity recognition of IgG by Fc γ RI allows it to trigger effector responses at lower low IgG concentrations in early immune responses. After binding to IgG, CD64 interacts with an accessory chain called the common gamma chain, which has an ITAM motif necessary for triggering the cell and for activation. It is usually constitutively expressed on monocytes and macrophages, and can be induced by neutrophils and eosinophils, where its expression is upregulated in bacterial infections and sepsis.