Host Fc gamma receptors and complement component C1q (FcγR/C1q)

Host Fc gamma receptors (FcγRs) and complement component C1q are the primary mediators of antibody-dependent effector functions in the immune system (NIH, 2017). FcγRs, including FcγRI (CD64), FcγRII (CD32), and FcγRIII (CD16), are expressed on various leukocytes and bind the Fc region of IgG antibodies to initiate antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP) (NIH, 2020). Complement component C1q is the recognition subunit of the C1 complex that initiates the classical complement pathway upon binding to antibody-antigen complexes, leading to complement-dependent cytotoxicity (CDC) (Nature Immunology, 2017). These components are essential for the therapeutic efficacy of monoclonal antibodies in oncology and infectious diseases, where they facilitate the clearance of target cells (NIH, 2024). Conversely, their over-activation or dysregulation is linked to autoimmune pathologies like systemic lupus erythematosus (SLE) and can contribute to antibody-dependent enhancement (ADE) of viral infections (MDPI, 2023). Therapeutic strategies often involve engineering the Fc region of antibodies to either enhance these interactions for increased potency or silence them to reduce inflammatory side effects (Nature Immunology, 2017). Specific drugs like ANX005 are being developed to directly inhibit C1q to treat neurodegenerative and autoimmune conditions (Annexon Biosciences, 2024).

Other names

Fc-gamma receptorsC1qIgG receptorsClassical complement pathway initiatorCD16CD32CD64FCGRComplement C1q

The mechanism of action involves the binding of the crystallizable fragment (Fc) of immunoglobulin G (IgG) to FcγRs on effector cells (e.g., NK cells, macrophages) to trigger intracellular signaling (ITAM/ITIM) and to C1q to initiate the classical complement cascade (NIH, 2017). This recruitment of humoral and cellular effector mechanisms leads to the neutralization, opsonization, and lysis of targeted cells or pathogens (Nature Immunology, 2017).