Fragment crystallizable region of immunoglobulin G (Fc region (of IgG))

The **fragment crystallizable (Fc) region of immunoglobulin G (IgG) antibodies** is the constant tail portion of the IgG molecule, composed mainly of the C-terminal domains of the heavy chains (CH2 and CH3), which mediates binding to cell surface Fc receptors and complement proteins[1][2][3][4][5][6]. This constant region determines effector functions critical for immune responses—including antibody-dependent cell-mediated cytotoxicity (ADCC), phagocytosis, and complement activation—by bridging antigen recognition (via the Fab regions) and the recruitment of immune effector mechanisms[1][2][7]. Fc region structure and glycosylation, particularly N-glycan on the CH2 domains, modulate its affinity for different Fc receptors (such as FcγRI, FcγRII, FcγRIII on immune cells) and for complement component C1q, leading to functional differences among IgG subclasses[1][2][4]. The Fc region is the main site for therapeutic antibody and Fc-fusion protein engineering, aiming to modulate half-life, effector function, and immunogenicity[2][4][5][7]. It is central to many diseases (e.g., cancer, autoimmune disorders, infections) as a mediator for antibody-based therapies, with Fc receptor polymorphisms and Fc glycosylation status serving as clinically relevant biomarkers[1][2][4]. Therapeutic manipulation of Fc–receptor interactions or FcRn-mediated recycling is an active area in immunology and drug development.

Other names

Fc region of IgGIgG FcFc domain (of IgG)Fragment crystallizable region (of IgG)

Engages Fc gamma receptors (FcγRs) on immune cells to trigger effector functions (e.g., ADCC, phagocytosis)[2][3][7] Binds and activates complement system (especially via C1q binding)[1][2][3] Interacts with neonatal Fc receptor (FcRn) for IgG recycling and prolonged half-life Allows formation of immune complexes and their clearance