Evidence That Fibronectin-Immunoglobulin Complexes Occur Normally in Plasma

This study was done to ascertain whether complexes of plasma flbronectin (PFn) and immunoglobulins (Igs) are normally present in plasma. P.F.n preparations from plasmas of six random human donors were analyzed for IgG, IgM, and IgA by competitive E.L.ISA procedures. To look for direct evidence of circulating complexes, two of the plasma samples were chromatographed on Sephacryl S-300. P.F.n prepared from a pool of three plasmas by cryoprecipitation was studied by crossed Immunoelectrophoresis to detect P.F.n-lg complexes. The Ig content of P.F.n ranged from 0.78% to 9.0% IgG; 0.25% to 4.9% IgM, and 0.15% to 0.71% IgA. The relative amounts were IgG < IgM < IgA in every sample, but the total Ig content of P.F.n varied with the plasma donor. The Sephacryl S-300 chromatogram of the plasma from which Ig-rich P.F.n was made showed distortion of the P.F.n peak by Ig peaks. P.F.n prepared by cryoprecipitation contained P.F.n-Immunoglobulin complexes. Plasma from adult beagle dogs was used to prepare canine P.F.n. IgM was detected in canine P.F.n by S.D.S-Page and by double diffusion experiments against antiserum to canine IgM. By crossed Immunoelectrophoresis, a P.F.n-IgM complex was detected in canine plasma. The cryoprecipitate recovered from a Sephacryl S-300 chromatogram of canine plasma contained equivalent amounts of IgM and P.F.n. These data suggest that complexes of Igs with P.F.n are normally present in plasma.