Fragment crystallizable region of immunoglobulin (Fc fragment (or Fc region))

The Fc fragment (Fragment crystallizable region) is the constant portion of an antibody produced by proteolytic cleavage, distinct from the antigen-binding Fab regions. It consists primarily of the C-terminal constant domains (CH2, CH3, sometimes CH4 for IgM/IgE) of the heavy chains. The Fc fragment is crucial for immune effector activity: it binds to Fc receptors expressed on various immune cells (including macrophages, NK cells, neutrophils), and to components of the complement system, mediating cell lysis, phagocytosis, degranulation, and clearance of opsonized targets. Fc glycosylation is critical for these functions. While not a standalone therapeutic target, engineering the Fc region is central to therapeutic antibody development, regulating their efficacy, serum half-life, and immune activation.

Other names

Fc regionFragment crystallizable regionImmunoglobulin FcFc tail

Mediates antibody-dependent cellular cytotoxicity (ADCC) via Fcγ receptor binding; Mediates antibody-dependent cellular phagocytosis (ADCP); Activates complement-dependent cytotoxicity (CDC) via complement protein binding; Modulates serum half-life via neonatal Fc receptor (FcRn) interaction.