C4BPB (C4b-binding protein β-chain) is a critical component of the complement regulatory system. C4b-binding protein (C4BP), a large glycoprotein in plasma, consists of seven α-chains and one β-chain (C4BPB) linked by disulfide bonds. Primarily synthesized in the liver, it regulates the classical and lectin complement pathways by binding to C4b, accelerating decay of C3 convertase, and acting as a cofactor for factor I-mediated proteolysis of C4b. This activity prevents excessive complement activation, protecting host cells from unintended damage.
C4BPB specifically interacts with the β-chain of C4BP, which also binds anticoagulant protein S, linking complement regulation and coagulation. Autoantibodies targeting C4BPB are clinically significant. In antiphospholipid syndrome (APS), anti-C4BPB antibodies disrupt C4BP-protein S interactions, impairing anticoagulant activity and promoting thrombosis. These antibodies are also detected in infections (e.g., streptococcal diseases) and autoimmune conditions like systemic lupus erythematosus (SLE), correlating with disease severity.
C4BPB antibodies are typically measured via ELISA, aiding in APS diagnosis and risk stratification. Research explores their role in vascular inflammation, pregnancy complications, and as therapeutic targets. Understanding C4BPB antibody dynamics offers insights into complement-related pathologies and personalized treatment strategies.