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

The Fragment crystallizable (Fc) region of Immunoglobulin G (IgG) is the tail portion of the antibody molecule, composed of the CH2 and CH3 constant domains of the heavy chains (Janeway et al., 2001, Immunobiology). It serves as the primary interface between the adaptive immune system and innate effector mechanisms, binding to Fc gamma receptors (FcγRs) on leukocytes and the C1q protein to initiate the complement cascade (Vidarsson et al., 2014, Frontiers in Immunology). A key regulatory interaction occurs with the neonatal Fc receptor (FcRn), which protects IgG from intracellular degradation and maintains its long half-life in the blood (Roopenian & Akilesh, 2007, Nature Reviews Immunology). In clinical practice, the Fc region is a major target for treating autoantibody-mediated diseases, where FcRn inhibitors are used to lower pathogenic IgG levels (Howard et al., 2021, The Lancet Neurology). Furthermore, the Fc region is a critical component of therapeutic monoclonal antibodies, often engineered to optimize their therapeutic index by enhancing or silencing immune effector functions.

Other names

Fc fragmentIgG Fc regionConstant region of IgGFc gamma

Therapeutic agents target the IgG Fc region primarily by inhibiting its interaction with the neonatal Fc receptor (FcRn). By blocking this salvage pathway, these drugs prevent the recycling of IgG back into circulation, leading to the rapid degradation of both healthy and pathogenic IgG antibodies (Gable et al., 2020, Frontiers in Immunology). Other strategies involve engineering the Fc region of monoclonal antibodies to modulate effector functions like ADCC or CDC (Wang et al., 2018, Protein & Cell).