Development and Applications of a Solid-Phase Radioimmunoassay for the P_0 Protein of Peripheral Myelin

Abstract

This is the first report of a quantitative radioimmunoassay for P_0. The assay uses antigen‐coated plastic microwells, with antibody binding detected by ^(125)I‐labeled protein A. Either peripheral myelin proteins or purified P_0 may be used as the antigen. Optimal extraction of tissue samples for P_0 immunoassay requires careful attention to the sodium dodecyl sulfate‐to‐protein ratio. Sodium dodecyl sulfate interference with antibody binding can be minimized by adding an excess of nonionic detergent and carrier protein to the incubation buffer. This method allows the detection of 0.8 ng of P_0 (20 ng/ml). Results from this assay showed little or no im‐munoreactivity in extracts of brain, central myelin, liver, purified myelin basic proteins, cultured, purified second ary Schwann cells, or membrane preparations from these cells. P0 was clearly detectable in Schwann cell cultures from 3‐ to 4‐day‐old rats at 12–18 h after dissociation (4% of the level in adult sciatic nerve) and in extracts of one‐day‐old rat sciatic nerve (2% of the level in adult nerve). Myelin basic protein radioimmunoassays showed that the ratio of P_0 to myelin basic protein is essentially constant in extracts of sciatic nerve from one‐day‐old, four‐day‐old and young adult rats. Another result was that P_0 levels are reduced in the trembler mouse sciatic nerve.

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