Fibrinogen binds IgG antibody and enhances IgG-mediated phagocytosis.

While Fibrinogen (Fg) and Immunoglobulin G (IgG) are traditionally thought to have separate functions in thrombosis and immune response, recent studies suggest overlapping functions. Here we present evidence that Fibrinogen binds to IgG specifically, and that Fibrinogen-IgG interactions enhance phagocytosis. We demonstrate specific, saturable binding of Fibrinogen to immobilized IgG and its fragments on nitrocellulose or poly-(L)-Lys styrene plates using Biotin/Streptavidin-Horse Radish Peroxidase detection systems. We also demonstrated that GFP-expressing E.coli coated with anti-E.coli antibody (IgG) and Fibrinogen elicit higher rates of phagocytosis than either Fibrinogen or IgG-treated E.coli alone (p < 0.001). We conclude that Fibrinogen enhances phagocytosis and possibly other leukocyte functions in concert with IgGs. This mechanism might focus leukocyte action triggered by fibrinogen towards specific antigens.