Polyethylene glycol antibody precipitation with

Skinner, R. P., and Maddison, P. J., Analysis of polyethylene glycol precipitates from SLE sera Antibody enrichment in association with disease activity. Clin. Exp. Rheum. 8, 553-560... 

In terms of overall efficiency, chemical precipitation of the bound fraction with ammonium sulfate or polyethylene glycol is often less satisfactory than systems such as second antibody. In particular, they tend to yield high assay blank values. However, for many routine assays this defect is compensated by their high level of practicality. 

Applicability—the ability to apply a single procedure to a wide variety of different assays—is desirable but not essential. Some procedures, such as second antibody and solid-phase antibody, are universal. Precipitation with ammonium sulfate or polyethylene glycol is not, because in some cases the properties of the antigen in the bound and free phases are not sufficiently distinct. 

Precipitation with salts, organic solvents and polyethylene glycol (PEG) has often been employed as an approach for fraction separation, which usually attracts the water essential for maintaining the 3D structure of antibody molecules, so that they precipitate [5]. Ammonium sulphate is a common salt used for antibody precipitation [125], but since it results in high levels of unspecific binding (i.e., 5-20%), it is seldom used nowadays for fraction separation purposes. 

Immunoglobulins can also be precipitated out of solution with polymers. The most frequently used polymer is polyethylene glycol (PEG or antifreeze). PEG tends to stabilize proteins and the antibody solution can be stored in the cold for long periods with PEG. 

Subsequently, it was found (101) that the presence of specificities el4 or el5 can be demonstrated by direct precipitation, using the Ouch-terlony method, if 2% polyethylene glycol (102) is incorporated in the agar. The authors suggested that the antigen is bivalent and that the linear complexes formed with bivalent antibody precipitate in the presence of polyethylene glycol the mechanism is not clear. 

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