Serum and plasma fibronectin binds to complement reacted immune complexes primarily via Clq.
The binding of fibronectin to human Clq, C3b, and complement-reacted immune complexes (IC) was investigated by enzyme-linked immunosorbent assays. Microplates were coated with BSA followed by incubation with rabbit-anti-BSA IgG or F(ab')2 fragments of rabbit anti-BSA. Incubation of the solid phase with serum at 37 degrees C caused attachment of Clq and C3b. Addition of EDTA to the serum inhibited the binding of C3b, but not Clq, whereas substitution of the anti-BSA IgG on the solid phase with the F(ab')2 fragments abrogated the Clq, but not the C3b binding. Fibronectin binding was observed after incubation of the solid-phase IC with serum or plasma at conditions where Clq was also bound, whereas only minor amounts of fibronectin bound to the solid phase IC via C3b. Purified fibronectin showed a dose-dependent binding to solid-phase IC pretreated with Clq or fibronectin-depleted serum, confirming that the binding of fibronectin to IC largely occurred via Clq. Significantly smaller amounts of fibronectin were bound to solid-phase IC incubated with plasma instead of serum, despite the higher fibronectin concentration in plasma. This difference was found not to be due to a fibrinogen-fibronectin interaction in plasma. Binding of fibronectin to preformed fluid phase IC incubated with serum was demonstrated by SDS-PAGE analysis of PEG-precipitated IC.
D000936:Antigen-Antibody Complex / Q000378:metabolism*; D003166:Complement Activating Enzymes / Q000378:metabolism*; D015922:Complement C1q; D003179:Complement C3b / Q000378:metabolism; D004492:Edetic Acid / Q000494:pharmacology; D005340:Fibrinogen / Q000494:pharmacology; D005353:Fibronectins / Q000378:metabolism*; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism; D012710:Serum Albumin, Bovine / Q000276:immunology
D000936:Antigen-Antibody Complex; D005353:Fibronectins; D007074:Immunoglobulin G; D012710:Serum Albumin, Bovine; D015922:Complement C1q; D003179:Complement C3b; D005340:Fibrinogen; D004492:Edetic Acid; D003166:Complement Activating Enzymes