Preparation and characterization of antisera to the myelin-associated glycoprotein.

Rabbits were immunized with the myelin-associated glycoprotein (MAG) that had been purified from isolated rat brain myelin by selective extraction with lithium diiodosalicylate (LIS) and phenol followed by preparative SDS gel electrophoresis. Antibodies to MAG were detected qualitatively by immunodiffusion and quantitatively by a double antibody assay utilizing [3H]fucose-labeled MAG as antigen. The antisera were capable of precipitating between 300 and 500 micrograms of MAG/ml of serum under the conditions of the assay. Preincubation of the anti-MAG serum with other glycoproteins or glycolipids did not inhibit the precipitation of labeled MAG. Similarly, preincubation of the antiserum with LIS-phenol extracts of non-neural tissues did not inhibit the immune precipitation of MAG. The specificity of the antiserum was also indicated by the selective double antibody precipitation of MAG from solubilized whole myelin that contained a heterogeneous mixture of [3H]fucose-labeled glycoproteins. The antibodies to MAG were not effectively absorbed by whole brain homogenate or purified myelin, indicating that the antigenic site(s) is not accessible in the intact membranes, but can be exposed by treatment with detergent or partial purification. Low levels of antibodies reacting with MAG were detected in three rabbits with experimental allergic encephalomyelitis induced by injection of purified myelin in complete Freund's adjuvant.