The spinal cord protein (SCP): appraisal of physiological and immunological hypotheses of anti-encephalitogenic action

Distribution of P2 antigen in neural and non-neural bovine tissues

Rabbit antisera to bovine nerve preparations were used to study the tissue distribution in the ox of P2, an antigen specific for the peripheral nervous system. Double diffusion gel precipitation tests were able to demonstrate P2 in spinal nerves, trigeminal nerve, spinal cord, medulla oblongata, and pons, but not in higher centers of the CNS, optic nerve, or non-neural tissues. A highly sensitive inhibition of enzyme immunoassay was developed to detect and quantitate low levels of P2. By this assay, P2 was found to be most concentrated in peripheral nerves, with decreasing amounts found in the spinal cord, medulla oblongata, pons, cerebellum, and cerebral peduncle. No P2 was found in the thalamus, cerebrum, or optic nerve; however, low levels of P2 were detected in the adrenal medulla, a non-neural tissue composed largely of cells derived from the embryonic neural crest region.

The protein antigens of peripheral nerve myelin

Peripheral nervous system (PNS) tissue contains a variety of proteins, lipids, and carbohydrates that may serve as immunogens in proving immune responses, as antigens participating in immunological reactions, or as both types of agents. Three proteins P0, P1, and P2, account for approximately 70% of PNS myelin proteins. P0 is the major PNS myelin protein and is restricted to the PNS. P1 is similar to, if not identical with, myelin basic protein, the component of central nervous system myelin which induces experimental allergic encephalomyelitis. P2 has neuritogenic properties for inducing experimental allergic neuritis and may be involved in immune-mediated PNS myelin injury in humans. The complete amino acid sequence for P2 has recently been delineated, and its neuritogenic, immunogenic, and antigenic features can now be further characterized.

Evidence that the bovine spinal cord protein is not an intrinsic component of peripheral myelin

Bovine spinal cord protein from peripheral nerve (BSCP-PN) was detected in the soluble fraction of the initial 0.8 M sucrose homogenate of bovine peripheral nerves by immunodiffusion analyses and by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The BSCP-PN in the soluble fraction of the 0.8 M sucrose homogenates was 25% of the BSCP-PN found in the soluble fraction of 0.3 M NaCl homogenates of peripheral nerve. BSCP-PN was also identified in purified bovine peripheral nerve myelin by immunodiffusion analyses and by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Densitometry data indicated that the BSCP-PN in myelin decreased from 25% of the total protein to approximately 8% when myelin was extracted with 0.3 M NaCl or 0.05 M HCl. The protein that remained in the BSCP-PN band of the NaCl-extracted myelin was identified as the periodic acid-Schiff II glycoprotein of peripheral myelin. Basic proteins such as BSCP-PN or lysozyme bound to myelin and to NaCl-extracted myelin when they were added to homogenates of myelin in 0.8 M sucrose. Pepsin, an acidic protein, did not bind to myelin under the same conditions. The results suggest that in 0.8 M sucrose, positively charged BSCP-PN released from the cytoplasm by homogenization binds to negatively charged myelin; thereafter, the BSCP-PN-myelin complex remains intact until it is dissociated in media of sufficiently high ionic strength. This interpretation is consistent with the immunohistological studies which demonstrated that BSCP-PN was not in the myelin sheath but was clearly localized in axons and in, or adjacent to, the Schwann cell basement membrane.

Evidence that rat peripheral myelin does not contain the rat spinal cord protein (RSCP-PN)

Rat spinal cord protein (SCP) from peripheral nerves (RSCP-PN) was not detected in purified rat peripheral nerve myelin by sodium dodecyl sulfate (SDS)-polyacrylamide slab gel electrophoresis or by immunodiffusion analyses using an anti-rat SCP in peripheral nerve (RSCP-PN) serum. The slab gel electrophoretic analyses also revealed that RSCP-PN has an appreciably lower molecular size than the component of rat peripheral myelin that is identified as P2 by its molecular size of 13,600 daltons. Thus, RSCP-PN and rat P2 are unrelated proteins.

Bovine-derived spinal cord protein (SCP) protects guinea pigs from experimental allergic encephalomyelitis (EAE) - a confirmatory report

An axonally localized, non-encephalitogenic protein derived from bovine spinal cord can protect guinea pigs from EAE following challenge with bovine myelin basic protein. Protection from neurologic signs is significant although CNS pathology is present. The protective regimen apparently varies depending upon the species and strain of animal; this specific requirement may account for a previous negative report.