Measurement of human nerve growth factor binding sites in brain and in peripheral tissues by a specific immunoprecipitation assay.

Using a monoclonal antibody against the human nerve growth factor (NGF) receptor (20.4 IgG), a specific immunoprecipitation assay for the quantitation of human NGF binding sites has been established. The procedure involves specific labeling of NGF receptors by covalent crosslinking to 125I-NGF with a carbodiimide reagent, and subsequent immunoprecipitation of the detergent-extracted 125I-NGF-receptor complexes with the 20.4 IgG. This two-site assay provides a specific method to measure NGF binding sites in peripheral tissues and central nervous system. Moreover, it allows analysis of the immunoprecipitated receptor species by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The finding that specific NGF binding sites are expressed on human neuronal and nonneuronal tissues, including lymphoid tissues, indicates that NGF exerts a broader physiological function than originally ascribed.