Experimental allergic encephalomyelitis in mice: encephalitogenicity of mouse central myelin basic proteins

Critical threshold for dose of myelin basic protein in murine autoimmune encephalomyelitis

The clinical and pathologic features of experimental allergic encephalomyelitis (EAE) in the SJL mouse are described after inoculation with different amounts of myelin basic protein (MBP) in adjuvant. A dose threshold was apparent in that 400 micrograms produced the most severe central nervous system (CNS) changes. These comprised an extensive multifocal destructive myelitis with minimal demyelination. Doses greater than 400 microgram produced less white matter pathology and showed demyelinative rather than destructive lesions. No CNS parenchymal changes were seen in animals given less than 400 micrograms. Inflammation was invariably present in all animals showing CNS pathology, a prominent cellular component of which was the polymorphonuclear leukocyte. These findings illustrate the relationship of clinical signs and pathologic changes to the dose of MBP administered. Thus, it has been shown that the dose requirements for MBP-induced EAE in the SJL mouse are different from and greater than those for other species and that, unlike rats and guinea pigs, lesions were more extensive. Although demyelination was present, lesions tended to be destructive in type. This murine MBP model may serve as an experimental analog for the acute destructive myelopathies occasionally associated with the human autoimmune demyelinating disorders.

Studies on myelin-basic-protein methylation during mouse brain development

The synthesis and methylation in vivo of myelin basic protein (MBP) during the mouse brain development has been investigated. When mice ranging in age from 13 to 60 days were injected intracerebrally with L-[methyl-3H]methionine, the incorporation of radioactivity into MBP isolated from youngest brain was found to be the highest and declined progressively in mature brains. This pattern of radioactivity incorporation was inversely correlated with the total amount of MBP in the brains, suggesting a higher ratio of MBP methylation to synthesis in younger brain. To differentiate the relative rate of protein synthesis and methylation, animals were given intracerebral injections of a L-[methyl-3H]methionine and L-[35S]methionine mixture and the ratio of 3H/35S (methylation index) was determined. The ratios in the isolated MBP fractions were higher than those of 'acid extracts' and 'breakthrough' fractions, with a maximal ratio in the youngest brain. This high ratio was well correlated with the higher protein methylase I (PMI) activity in younger brains. The MBP fractions were further separated on SDS/polyacrylamide-gel electrophoresis into several species with apparent Mr ranging from 32,400 to 14,500. The results indicated that each protein species accumulated at a characteristic rate as a function of age. The high-Mr (32,400) species was predominant in younger brain, whereas the smaller MBP was the major species in older brain tissue. The importance of this developmental pattern of MBP synthesis and methylation is discussed in relation to PMI activity.

Delayed, relapsing experimental allergic encephalomyelitis in mice. Role of adjuvants and pertussis vaccine

The effect was studied of varying the dosage of mycobacteria and pertussis vaccine in the immunization emulsion on the development of delayed, relapsing experimental allergic encephalomyelitis (DR-EAE) in SJL/J mice. DR-EAE could be induced with dosages of mycobacteria from 0.2 mg to 1.0 mg per mouse. Animals given pertussis vaccine from different batches and different sources all developed DR-EAE with similar percentages of animals sick, animals relapsing, and delay to onset. Mice immunized without pertussis vaccine also developed DR-EAE but had fewer relapses and a longer delay to onset. The role of antigens and adjuvants in relapsing EAE and analogies with multiple sclerosis are discussed.