Antibody fragment crystallizable region (Fc region) (Fc region)

The Antibody fragment crystallizable (Fc) region is the tail portion of an immunoglobulin molecule that mediates essential effector functions of the immune system [1]. It consists of the constant domains of the antibody heavy chains (CH2 and CH3 in IgG) and serves as the interface between the adaptive immune response and innate effector mechanisms [1]. By binding to various Fc gamma receptors (FcγRs) on leukocytes, the Fc region triggers processes such as antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) [1, 3]. It also interacts with the C1q component of the complement system to initiate complement-dependent cytotoxicity (CDC) [1]. Furthermore, the Fc region's interaction with the neonatal Fc receptor (FcRn) is the primary mechanism regulating the long serum half-life of IgG antibodies through a pH-dependent recycling pathway [2]. In drug development, the Fc region is frequently engineered to enhance therapeutic efficacy, reduce side effects, or extend the duration of action of monoclonal antibodies and Fc-fusion proteins [3]. Conversely, blocking the Fc-binding site on FcRn has emerged as a potent strategy to treat autoantibody-mediated diseases by accelerating the clearance of pathogenic IgG [4].

Other names

Fc fragmentConstant region of immunoglobulinIgG Fc domainFragment crystallizable region

The Fc region mediates immune responses by binding to Fc gamma receptors (FcγRs) to trigger ADCC and ADCP, and to C1q to initiate CDC [1, 3]. It also binds to the neonatal Fc receptor (FcRn) to protect IgG from lysosomal degradation, thereby extending its half-life [2]. Therapeutic modulation involves engineering the Fc region to alter these affinities or using FcRn antagonists to block the Fc-FcRn interaction and promote the clearance of endogenous IgG [4].