Radioimmunoassay of myelin basic protein. A methodological evaluation.

Three techniques for separating free antigen from antigen-antibody complexes have been applied to radioimmunoassay of myelin basic protein: cold ethanol precipitation of complexes, dextran-coated charcoal precipitation of free antigen, and second antibody precipitation of complexes. After optimization of the incubation and separation steps, the 3 methods were evaluated for precision and accuracy when applied to both spinal fluid and brain tissue homogenates. For determinations in brain tissue all 3 methods showed the same precision and gave largely the same values, though the ethanol method gave slightly lower levels. For spinal fluid the ethanol and dextran-charcoal methods gave the same values, but the double antibody method gave values only 1/3 as high. With spinal fluid, the precision of the dextran-charcoal method was poor compared with that of the other two. The double antibody method proved to be the method of choice for brain tissue samples, when the results of the incubation and separation steps, and the precision and accuracy of the determinations were taken into account. However, for an unknown reason values for spinal fluid were too low by this method. Therefore the ethanol precipitation method is recommended for spinal fluid samples and the double antibody method for brain tissue samples.