Format determinants of synthetic myelin basic protein peptide S82 mimicked by a mixture of synthetic peptides S8 and S79

Immunochemical analysis of Lewis rat antisera to the synthetic encephalitogenic peptide S49

Discrete populations of anti-S49 antibodies were found in the antisera of Lewis rats recovered from S49-induced experimental allergic encephalomyelitis (EAE). A potent inducer of EAE in Lewis rats, S49 is a synthetic peptide representing residues 69-84 of bovine myelin basic protein but with deletions at Gly-77 and His-78 to form an analogue of guinea pig or rat 69-84, GSLPQKAQRPQDENG. Each population within a given antiserum, as identified by Scatchard and Sipsian window analysis, was found to exhibit reactivity for a different S49 determinant, and the affinities of each population were relatively restricted and discontinuous. The high affinity populations (10(7)-10(8) M-1) were cross-reactive with YS8 (YGSLPQKAQGHRPQDENG) in equilibrium competitive inhibition reactions whereas the low affinity populations (10(5)-10(6) M-1) were reactive only with S49 and YS49 among a panel of peptide analogues. Of the YS8 cross-reactive antibodies the highest affinity (10(8) M-1) were also cross reactive with S81 (YGSLPQKAQGHRPQDEG) but not S49 (69-84-Gly), thus emphasizing the need for Tyr-68 for format stability of the determinant involved. The other YS8 cross-reactive population (10(7) M-1) was completely reactive with S49 but totally unreactive with S81 in equilibrium reactions, thus emphasizing the requirement for Asn-84 but not Tyr-68 for the determinant's topographic stability. Peptides shorter than S49 from the N-terminal end, but retaining the sequences AQRPQDEN or SQRSQDEN (suspected residence of minimal encephalitogenic determinants), reacted only under conditions of two-step non-equilibrium competitive inhibition assays. Such reactions would occur only at very low affinity (less than 10(5) M-1) with the anti-S49 antibodies. It was hypothesized that the encephalitogenic T-cell determinant for Lewis rats, although permitting B-cell responses at very low affinity, may exclude high affinity responses in susceptible animals.

Affinity purification of two populations of antibodies against format determinants of synthetic myelin basic protein peptide S82 from S82-AH- and S82-CH-Sepharose 4B columns

Two different kinds of immunosorbents were prepared that contained the synthetic myelin basic protein didecapeptide S82 (TTHYGSLPQKAQGHRDQDEG)--one coupled with AH-Sepharose 4B through hexanoate spacers to the C-terminal glycyl residue; the other, with CH-Sepharose 4B through hexanoate spacers to the N-terminal threonine residue. An antiserum rich in antibodies to a format determinant of S82 was passed through each column, and, by means of affinity purification, two homogeneous populations of anti-format antibodies were obtained, each with a binding affinity of 1 X 10(8)M-1 for S82. The population recovered from S82-AH-Sepharose 4B cross-reacted to a considerable extent with synthetic peptide S8 (GSLPQKAQGHRPQDENG) but only to a limited extent with S79 (AQGHRPQDEG). The population recovered from S82-CH-Sepharose 4B cross-reacted poorly, if at all, with S8. An equimoler mixture of S8 + S79, however, reacted well with either population of anti-format antibodies, thus showing that the mixture could mimic the format of S82. It was concluded that secondary structural conformation of S82 could be preserved during the coupling procedure and that the resulting immunosorbents could be used for the affinity purification of anti-S82 antibodies to the format determinants.