Cryoprecipitogogue from normal serum: mechanism for cryoprecipitation of immune complexes

We designed this study to examine the relationship of cryoglobulins to immune complexes in sera of patients with rheumatic or infectious diseases. Polyethylene glycol was used to precipitate large proteins from normal serum and then was dialyzed away. The precipitated proteins were soluble in warm phosphate-buffered saline but at 4 degrees C they reversibly reprecipitated. As they reprecipitated, they selectively coprecipitated cold-soluble immune complexes. By NaDodSO4/polyacrylamide gel electrophoresis, these normal, nonimmunoglobulin cryoproteins were similar to the nonimmunoglobulin constituents of washed cryoimmunoglobulins from patients with rheumatic or infectious diseases. These findings suggest that cryoprecipitability is a property not of immune complexes themselves but of a group of large normal serum proteins. In inflammatory diseases, the concentrations of some of these proteins, responding as acute-phase reactants, may increase to the point where intermolecular attractive forces become prominent, particularly in the cold. Cold-augmented molecular aggregation between these nonimmunoglobulin proteins and immune complexes could then act to decrease their collective solubility and result in the cryoprecipitation of otherwise cold-soluble immune complexes.