A quantitative study of encephalitogenic protein and peptides in guinea pigs.

The encephalitogenic activity of bovine encephalitogenic protein (EP) at at doses from 1 to 33.5 microgram was studied in guinea-pigs. Anencephalitogenicity can be demonstrated at a dose of 1 microgram of EP when given with Freund's complete adjuvant. An increase in the dose of EP results in an increase in encephalitogenicity. Data from a previous paper (Lindh and Bergstrand 1975) supplemented with new data on the encephalitogenic capacity of peptide 89--169 were compared concerning the incidence and strength of experimental allergic encephalomyelitis (EAE) to determine the relative contribution of the various parts of EP to the encephalitogenic properties of the total molecule. Peptide 89--169 shows the same degree of encephalitogenicity as EP, but when the tryptophan residue is blocked (HNB-89-169) the encephalitogenicity is reduced to approx. 15% of the initial amount. Peptide 43--115, tyr (modified at the tyrosine residue 67) appears to have an encephalitogenicity of rather less than 10% of the intact EP molecule, whereas peptide 1--42, if active at all, has an encephalitogenicity of approx. 1% of the total EP molecule. The findings are discussed in the light of a possible cross-reactivity between different determinants of EP.