Quantification of IgG by the ammonium sulfate technique—I. Interference of the primary interaction between 125I Fc and rabbit anti-human Fc

Abstract

A sensitive, reproducible method to quantitate human IgG, utilizing 125I Fc, derived from either the papain sensitive (ps) or papain resistance (pr) conformational forms of IgG, as the test antigen in the ammonium sulfate technique is described. Since 125I Fc fragments so obtained are innately soluble in 45 per cent saturated ammonium sulfate, free antigen may be separated from bound antigen-antibody complexes. The test system takes advantage of the capacity of IgG containing materials to block the interaction between human 125I Fc and a standard rabbit anti-human Fc.