Human immunoglobulin Fc region (Fc region)

The Human immunoglobulin Fc (fragment crystallizable) region is the C-terminal portion of an antibody molecule, composed of the constant domains of the heavy chains. It serves as the critical link between the adaptive immune system's specificity and innate effector mechanisms by binding to Fc receptors (FcRs) on leukocytes and the C1q component of the complement system (Janeway's Immunobiology, 2017). These interactions facilitate essential immune processes, including antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-mediated lysis (Wang et al., 2018, Nature Reviews Drug Discovery). Beyond effector functions, the Fc region interacts with the neonatal Fc receptor (FcRn) in a pH-dependent manner to protect IgG from lysosomal degradation, thereby extending its serum half-life to approximately three weeks (Roopenian & Akilesh, 2007, Nature Reviews Immunology). In modern pharmacology, the Fc region is a primary target for FcRn antagonists like efgartigimod, which are designed to lower the levels of pathogenic autoantibodies in diseases such as myasthenia gravis (Howard et al., 2021, The Lancet Neurology). Additionally, the Fc region is frequently used as a scaffold for Fc-fusion proteins to improve the stability and pharmacokinetics of therapeutic peptides and receptors (Gessner et al., 1998, Annals of the Rheumatic Diseases).

Other names

Fragment crystallizable regionFc domainIgG Fc regionImmunoglobulin G Fc fragment

Therapeutic agents targeting the Fc region primarily function by modulating its interaction with Fc receptors. FcRn antagonists bind to the neonatal Fc receptor to block the recycling of endogenous IgG, leading to the rapid clearance of pathogenic autoantibodies from circulation (Howard et al., 2021, The Lancet Neurology). Other strategies involve using the Fc region as a fusion partner to extend the half-life of therapeutic proteins or engineering the Fc domain to enhance or silence effector functions like ADCC and CDC (Wang et al., 2018, Nature Reviews Drug Discovery). Additionally, enzymes like imlifidase can specifically cleave the Fc region to neutralize IgG-mediated inflammation (Lonze et al., 2018, Annals of Surgery).