期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1978
卷号：75
期号：8
页码：4042-4046
DOI：10.1073/pnas.75.8.4042
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：High levels of nerve growth factor (NGF) determined by competition radioimmunoassay do not agree with values obtained by bioassay. This discrepancy is illustrated here with rat and mouse serum as examples in which values up to 1000 ng/ml have been found by using competition radioimmunoassays. An explanation for the discordant results is presented: serum components bind NGF with an intermediate affinity (Kd = 10(-7) M) but with a very large capacity (up to 0.5 mg of NGF per ml of rat serum). The binding of 125I-labeled NGF to serum components competes with the binding to the solid-phase antibodies (Kd = 10(-9)M) present in limiting amounts, according to the principle of competition radioimmunoassays. Thus, less radioactivity is recovered bound to the antibodies and this gives the erroneous impression that NGF is present. To overcome this difficulty, a two-site radioimmunoassay has been developed which utilizes nonlimiting numbers of antibody binding sites. This assay provides a reliable determination of NGF levels in serum and it can be shown that in rat and mouse serum (either sex) there is less than 5 ng of NGF per ml, in agreement with the results of the bioassay.
