A neurochemical and immunocytochemical study of P2 protein in human and bovine nervous systems.

The anatomical distribution of P2 protein was studied in human autopsy tissue. Spinal cord (SC) and peripheral nerve (PN) were stained by the peroxidase-antiperoxidase method with antisera to bovine P2, glial fibrillary acidic protein, and myelin basic protein (BP). P2 antiserum did not stain all of the myelin in the PN. The staining was randomly distributed and discontinuous along a given myelinated axon. P2 antiserum also stained SC myelin in a pattern similar to the PN. Only a fraction of the sheaths stained, in contrast to BP antiserum that stained all myelin sheaths in both the SC and PN. P2-positive myelin was distributed throughout the SC white matter, including an occasional myelinated fiber in the SC grey matter. P2 and BP antisera did not stain regions of demyelination in a case of idiopathic polyneuritis, while adjacent myelinated PN stained normally. Absorption of the P2 antiserum with P2, bovine PN or bovine SC (carefully dissected to eliminate PN contamination) nullified the specific staining in both the PN and SC; however, absorption with BP or hemispheric myelin did not eliminate P2 staining. The P2 antiserum formed a single immunodiffusion line with pure P2 and acid extracts of bovine SC and PN myelin, but not with an acid extract of bovine hemispheric myelin. Electrophoresis of defatted bovine SC produced a distinct band corresponding to P2. Therefore, three lines of evidence, immunocytochemical, immunodiffusion and electrophoretic, suggest that P2 is present in PN and SC but not in hemispheric myelin.