A Simplification of the Radioactive Antigen-Binding Test by a Double Label Technique

Abstract

Abstract The radioactive antigen-binding test developed by Farr is a relatively simple quantitative technique to measure primary antigen antibody interaction (1). The principle of the test is that radioactive antigen will remain bound to antibody when the latter is precipitated with ammonium sulfate. To quantitate the test one may either determine the radioactivity of the precipitated globulins after washing them with half-saturated ammonium sulfate or, alternatively, one may determine the amount of radioactive antigen remaining in the supernatant. Both of these methods become technically difficult when one is dealing with very small volumes of sera, which may become necessary when working with small animals or with human specimens obtained by fingerstick. It is the purpose of this communication to present an alternative method that requires neither the removal of an accurate sample of the supernatant nor the washing of the precipitate. The basis of this method is to add radioactive 22Na to the 125I-labeled antigen as a volume marker.