Immunoglobulin G Fc region (IgG Fc region)

The **Immunoglobulin G Fc region** is the constant tail portion found in all human IgG antibodies. It is composed primarily of paired CH2 and CH3 domains from each heavy chain. Unlike Fab regions that bind antigens specifically, the **Fc** ("fragment crystallizable") mediates interactions with various cellular receptors—most notably **Fc gamma receptors** on innate immune cells—and proteins such as C1q from the complement system. These interactions enable key antibody effector functions including opsonization, phagocytosis, antibody-dependent cellular cytotoxicity (**ADCC**), degranulation responses in granulocytes/mast cells/basophils/eosinophils, regulation of serum half-life via neonatal **Fc receptor** (**FcRn**) binding, placental transfer during pregnancy, and initiation/amplification/modulation of inflammation. The structure includes a highly conserved N-glycosylation site at Asn297; modifications here critically influence both stability and functional engagement with downstream effectors like complement proteins and cell-surface receptors. The sequence homology among different subclasses is high (>90%), but subtle differences—especially in hinge regions—modulate subclass-specific activities. In therapeutics development, engineering changes within this domain can enhance desired clinical effects such as increased ADCC/CDC activity against cancer targets while minimizing adverse events by reducing unwanted activation pathways.[1][2][3]

Other names

Fc region of immunoglobulin GFragment crystallizable region of IgGIgG-Fc fragmentFcγ (for gamma heavy chain-specific receptors)

For drugs utilizing the Immunoglobulin G Fc region, mechanisms include: Engagement with immune cell surface receptors (FcγRs) to trigger ADCC or phagocytosis[2][3]; Activation of complement cascade leading to cell lysis (CDC)[1][3]; Modulation of serum half-life by interaction with neonatal Fc receptor (FcRn), affecting recycling and degradation rates[3].