A new pattern of spinal-cord demyelination in guinea pigs with acute experimental allergic encephalomyelitis mimicking multiple sclerosis.

A technique is described for producing large demyelinating lesions of the spinal cord in the guinea pig. Guinea pigs were pretreated by immunization with ovalbumin and water-soluble adjuvant (N-acetyl-muramyl L-alanyl D-isoglutamine, MDP) in water-in-oil emulsion (Freund's incomplete adjuvant). They were given a large dose (10 mg) of ovalbumin i.p. one month later. After a few weeks the animals were sensitized with guinea-pig basic protein in Freund's complete adjuvant. Five out of 11 animals developed large, distinctive, sharply demarcated, symmetrical demyelinating lesions within 30 days. These lesions occurred in the dorsal and anterior columns, root entry zones and subpial region of the spinal cord. Histology showed a considerable amount of free lipids. There were also infiltrative lesions of classical experimental allergic encephalomyelitis (EAE) of normal severity in the same animals. The demyelinating lesions resembled those seen in multiple sclerosis in their location and extent in the spinal cord and in the presence of free lipids. Control experiments indicated that pretreatment with ovalbumin/MDP and the second injection of ovalbumin was necessary for all the demyelination; moreover guinea pigs immunized with basic protein in Freund's complete adjuvant or Freund's incomplete adjuvant plus MDP without pretreatment only developed classical EAE with minimal or no demyelination.