Spontaneous and experimental neuritis and the distribution of the myelin protein P2 in the nervous system.

The P2 contents of nervous tissues from the human, rabbit, guinea pig, and Lewis rat were measured by radioimmunoassay. The ventral spinal roots contained more P2 than any other tissue. Human dorsal roots and peripheral nerves contained 41-65% of the amount in human ventral roots. Human olfactory and optic nerves and brain contained 1.1-2.7%, spinal cord, 2.8%, cranial nerve VIII, 11%, and cerebral grey matter, 0%. The relative amounts in the rabbit nervous system were similar except that the spinal cord contained 20% of the amount in the ventral roots. Qualitative estimates in the guinea pig showed that the spinal roots and peripheral nerves contained more P2 than the spinal cord, and that none was present in the brain. In the Lewis rat, P2 could be detected in the spinal roots and peripheral nerves but not in the CNS. The distribution of P2 in the human nervous system parallels the incidence and severity of lesions in acute polyradiculoneuritis. It also explains the absence of any lesions in the CNS when experimental allergic neuritis is induced in the Lewis rat.