Detection of Antibodies and Soluble Antigen-Antibody Complexes by Precipitation with Polyethylene Glycol

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Abstract
Polyethylene glycol (PEG) was used in a modification of the Farr antigen binding test in order to separate free antigen from antibody-bound antigen. Most of the immunoglobulins are precipitated at 20% PEG while smaller antigens like bovine serum albumin or insulin are quite soluble at this concentration of PEG. Such antigens are therefore precipitated in 20% PEG if they are bound to antibodies. Furthermore, PEG has been used at lower concentrations in order to precipitate soluble antigen-antibody complexes in conditions at which free antigen or free antibody would be soluble. This second method could be applied to larger antigens such as IgG or thyroglobulin.