The antigenic reactivity of small fragments derived from human myelin basic protein peptide 43-88

In an effort to develop immunochemical reagents for detecting small peptides originating from myelin basic protein (BP), the antigenic determinants of fragments from human BP peptide 43-88 were examined. Antisera were produced in nine sheep and forty rabbits immunized with BP, BP peptide 43-88, or a region derived from within or containing a portion of BP peptide 43-88. These included custom synthesized peptides 51-67, 67-80, 74-84, 79-88, and 83-95. Reactivities were assessed by double antibody radioimmunoassay (DA-RIA) using radiolabeled BP or BP peptides. For peptides 74-84, 79-88, and 83-95 it was necessary to synthetically add a terminal tyrosine residue for radioiodination. Antisera to peptides 51-67, 67-80, 74-84, 79-88, and 83-95 showed much greater reactivity with the homologous antigen, with variable, but sometimes no, reactivity against BP or BP peptide 43-88. This was particularly evident in displacement DA-RIA. Of the small peptides, antisera to whole BP reacted best with peptide 83-95, whereas antisera to peptide 43-88 reacted best with peptide 79-88. Placement of the synthetically added tyrosine had a marked influence on the reactivity of BP peptide 79-88: antisera to BP peptide 43-88 reacted much better with radioiodinated tyrosinyl peptide 79-88 than with radioiodinated peptide 79-88-tyrosine. These results indicate that within a region of BP encompassing residues 51 through 95 a number of potential antigenic determinants exist. Some of the determinants on the small peptides represent distinctive conformational determinants or are inaccessible in BP peptide 43-88. The ability to detect small BP peptides by immunoassay necessitates that the identity of the peptide be known and that antibody reagents capable of reacting with the peptide(s) be available.