S. H. Stone

Progressive Demyelination and Reparative Phenomena in Chronic Experimental Allergic Encephalomyelitis

Chronic experimental allergic encephalomyelitis (EAE), produced in inbred guinea pigs given a single inoculation during the juvenile period with isologous spinal cord in complete Freunds adjuvant, has been studied by light and electron microscopy. Most animals showed a delayed onset of nurologic signs from 12 to 68 weeks post-inoculation (PI), while several were asymptomatic up to 74 weeks PI. Two animals showed a relapsing clinical course. Examination of the spinal cords of all animals revealed chronic demyelination, remyelination, and recent demyelination. Marked perivascular inflammation, including plasma cells, was seen within demyelinated plaques. The usual type of central nervous system (CNS) remyelination was documented but in addition, remyelination of CNS axons by invading Schwann cells was noted. This Schwann cell invasion, not previously seen in EAE, was predominantly in the area of the root entry zone, and occasionally involved extensive areas of the dorsal or ventral horns. The extent of Schwann cell invasion, as well as the usual CNS-type remyelination, demonstrates the reparative capacity of the CNS. The recurrent clinical and morphologic changes in these long-term animals provides further evidence that this model of chronic EAE has many features reminiscent of multiple sclerosis. The underlying immunologic mechanisms responsible for the recurrent disease in these animals are unknown. The presence of plasma cells in the inflammatory exudates might suggest a role for B cells in these chronic animals. The possibility of an intermittent release of loculated adjuvant/antigen accounting for the recurrent disease was considered.

Experimental allergic encephalomyelitis--migration of early T cells from the circulation into the central nervous system.

Study of lymphocytes from the blood of guinea pigs with acute EAE induced by isologous spinal cord in adjuvant reconfirmed that in comparison to normals, the percentage of early (active or high affinity rosetting) T cells decreases dramatically and that these changes can be correlated with clinical signs. In addition, we have investigated matching samples of CNS infiltrating cells recovered by ultrasonication and have found that coinciding with the decrease in early T cells in the circulation, significantly higher levels (P less than 0.001) of these cells appear within the CNS compartment; It is concluded that the decrease of early T cells in the circulation is caused by their migration to the target organ, the CNS.

Glial bridges and Schwann cell migration during chronic demyelination in the C.N.S.

SummaryThe formation of fibrotic bridges from subpial astrocytes into the subarachnoid space of the spinal cord and the migration of Schwann cells to the central nervous system (C.N.S.) is appraised in chronically demyelinated C.N.S. lesions. Spinal cord tissue was studied from inbred, Strain 13 guinea pigs with chronic experimental allergic encephalomyelitis (EAE). It has been found that uncommitted Schwann cells are present around remyelinated fibres in nerve root entry zones, between meningeal cells at a distance from the roots and along blood vessels within the spinal cord parenchyma. It is speculated that these cells migrate via the above route to the C.N.S. In the present model, this invasion might be aided by glial fibrosis, a process which leads to surface irregularities in the spinal cord, an extensive extracellular space and possible breaches in the glia limitans through which Schwann cells might penetrate.

Chronic relapsing experimental allergic encephalomyelitis: CNS plaque development in unsuppressed and suppressed animals

SummaryCentral nervous system (CNS) lesion morphology has been studied in inbred Strain 13 guinea pigs sensitized for chronic relapsing EAE in which the disease was either left to develop (unsuppressed) or was suppressed with injections containing myelin basic protein (MBP). Pathologic changes correlated well with clinical activity. In unsuppressed chronic EAE animals, active clinical disease was invariably matched by acute inflammation in the CNS. In more chronic states, the CNS displayed fibrosis and remyelination while response showed the CNS to contain recent changes superimposed upon old lesions. In animals in which the disease was suppressed by injections of MBP, clinical signs did not develop. However, some early subclinical changes were seen morphologically. These lesions were able to remyelinate early on and there was no progression in lesion formation. Apparently, therefore, MBP had a beneficial effect upon the course of the disease and had promoted structural repair. It thus appears that MBP therapy might be one effective approach for the prevention of chronic relapsing EAE. The findings should prove relevant to future MBP trials in multiple sclerosis.

Dose-dependency of MBP-induced demyelination in the guinea pig☆

The pathology of experimental allergic encephalomyelitis (EAE) induced by bovine myelin basic protein (MBP) has been examined in the guinea pig with a series of doses ranging from 37.5 micrograms to 600 micrograms. This was to investigate whether the previously demonstrated lack of demyelinative effect by MBP was dose-related. At all doses tested, MBP induced clinical disease. Inflammation was the major feature of lesions in all animals. However, no demyelination was seen when 75 micrograms MBP or less was given. At higher doses (150 micrograms upwards), MBP always induced intense inflammation but demyelination was encountered inconsistently. These observations support the contention that in addition to an immune response to MBP, other factors contribute to autoimmune demyelination.

Cataracts and Allergic Encephalomyelitis

Juvenile guinea pigs developed cataracts during severe acute allergic (autoimmune) encephalomyelitis produced actively by injection of central nervous system antigens in complete Freund’s adjuvants. C