Sites in Myelin Basic Protein that React with Monoclonal Antibodies

The epitopes (antigenic sites) for seven monoclonal antibodies (MAbs) evoked in rats or mice by guinea pig or monkey myelin basic protein (BP) have been located in four different sequences of the BPs extracted from various species. Six of the MAbs were evoked by guinea pig BP. (1) One epitope, possibly a pair, is included within residues 1-14 of all BPs tested and reacts with two rat IgG MAbs. (2) A definite pair of overlapping epitopes includes the central Phe91-Phe92 sequence. One epitope is contained entirely within sequence 90-99 and reacts with a rat IgG MAb. The substitution of Ser in chicken BP for Thr97 destroys this epitope. The other epitope appears to include residues on the amino side of Phe44 and even of His32 and suggests some tertiary structure in BP. This epitope reacts with a mouse IgM MAb that does not recognize the chicken substitution. (3) The third epitope lies within residues 114-121, specifically including Trp118, and reacts with a rat IgG MAb. A cross-reacting epitope probably includes residues 44-45 in certain species (guinea pig and bovine but not rabbit). (4) Another pair of epitopes is located within residues 131-140 but is severely species-restricted. This region in guinea pig BP evoked a species-specific mouse IgM MAb. The same region in monkey BP evoked the seventh MAb, a mouse IgG, which reacts with human, chimpanzee, monkey, bovine, and rat-18.5 kDa BPs and to a lesser extent rabbit BP but not with guinea pig, pig, or chicken BPs. Some tertiary structure in guinea pig BP is also suggested by the reactivities with the IgM MAb. All of the MAbs react with myelin in histologic preparations, but the optimum method of preparation of the tissue varies with each.