Artifactual presence of β-nerve growth factor in adult mouse brain

Adult male mouse brain extracts were determined to contain 0.7 ng β-nerve growth factor (NGF)/mg total protein in a one-site radioimmunoassay (RIA) and 3.6 ng NGF/mg protein in a competition radioreceptor assay using PC 12 cells. When brain extract were immunoprecipitated with antiserum to NGF prior to use in a radioreceptor assay, no reduction in measured NGF content resulted, whereas immunoprecipitation of submaxillary gland extract reduced the NGF level by 83–100%. The immunoassay and radioreceptor assay were then modified by incubating antisera or PC 12 cells first with brain extract, and then, after washing, with ¹²⁵I-labeled authentic mouse NGF. In the modified assays, no NGF was detected in the extracts, indicating that adult mouse brain does not contain NGF itself but does contain an NGF-binding component that causes false positive results in standard one-site RIAs and competition radioreceptor assays.