Spontaneous remission of autoimmune encephalomyelitis is inhibited by splenectomy, thymectomy or ageing.

Experimental autoimmune encephalomyelitis (EAE) can be induced in genetically susceptible animals by injecting them with basic protein of myelin (BP) in a suitable adjuvant. EAE in adult Lewis rats is expressed clinically by acute paralysis and histologically by mononuclear cell infiltration of the central nervous system. Most rats spontaneously recover from EAE and show little or no damage to myelin. We report here that chronic progressive EAE with marked myelin lesions can be induced by a single injection of BP in complete Freund's adjuvant in intact 13-month old rats, or in 4-month old rats provided they have been splenectomized. Juvenile 2 1/2-month old rats recover spontaneously despite splenectomy. Thymectomy of young adult rats leads to relapsing EAE. These results illustrate that the clinical course of EAE is markedly influenced by age and integrity of immune organs. Furthermore, they provide an experimental model with features similar to those of chronic relapsing disease of the nervous system of man.