Large subpial plaques of demyelination in a new form of chronic experimental allergic encephalomyelitis in the guinea pig.

The current report describes a new technique for producing chronic experimental allergic encephalomyelitis (EAE)+ accompanied by demyelination in adult strain 13 guinea pigs. The disease is induced by a combination of passive transfer of lymph node cells sensitized to myelin basic protein (BP) and active challenge of the recipients with homologous spinal cord in Freund's complete adjuvants. The clinical-pathologic spectrum ranges from a progressively fatal form of chronic EAE leading to death in 4-7 wk, through a remitting-relapsing form, to a chronic-stable form lasting many months. In all of these forms large subpial plaques of demyelination occur in the spinal cord with active phagocytosis of myelin debris, especially at the edges. The axons are swollen, but remain intact throughout. The histologic appearances of the lesions suggest that lysis of myelin occurs before phagocytosis, one of the hypotheses proposed for the pathogenesis of lesions occurring in humans with multiple sclerosis.