An immunochemical analysis of a myelin basic protein serum factor: Cross reactivity with residues 69–71 of the rabbit encephalitogenic sequence 65–74 of myelin basic protein

Abstract

A partially purified myelin basic protein serum factor (MBP-SF), cross-reactive with residues 65–74 (TTHYGSLPQK) of myelin basic protein, has been employed in an immunochemical study to identify the nature of the cross-reacting determinant, more precisely. To probe the structural requirements of this determinant, Scatchard inhibition analyses and competitive peptide inhibition radioimmunoassays were employed with a series of peptide analogs of the 65-74 region and with three different reagent antisera: a rabbit anti-rat myelin antiserum (#My05) and two antisera, one rabbit (#162) and one chicken (#66), raised against synthetic peptide S24 (TTHYGSLPQKG). Scatchard inhibition analyses with MBP-SF revealed specific inhibition of binding of ¹²⁵I-S24 to #162 and #My05, but not to #66. Further delineation of the structural requirements of the cross-reactive determinant, employing a liquid-phase radioimmunoassay, revealed a unique reactivity pattern for the chicken anti-S24 antiserum which, unlike #162 and #My05, did not cross-react under high-affinity conditions with synthetic peptide S20 (GSLPQK, representing the C-terminal half of S24). This, in concert with the Scatchard data, is suggestive of the presence of a cross-reactive determinant centered around residues 69–71 of MBP.