Clonotypic heterogeneity of Lewis rat T cells specific for the encephalitogenic 68-86 region of myelin basic protein

Abstract

Experimental autoimmune encephalomyelitis was induced in a Lewis rat by sensitization with synthetic peptide GP68-86, representing the 68-86 sequence of guinea pig myelin basic protein (GPMBP). To delineate T cell determinants of GP68-86, lymph node cells from this rat were activated in culture with GP68-86 and were fused with cells of the mouse thymoma BW5147. The resultant hybrids were cloned by limiting dilution and screened for GP68-86-evoked secretion of IL2 in the presence of rat splenocytes. Twelve T cell hybrids derived in this manner were tested for reactivity to different heterologous species of MBP as well as to substituted or truncated analogs of GP68-86. The hybrids generally exhibited potent reactivity to GPMBP but differed markedly in their reactivity to autologous rat MBP (RMBP). A few exceptional hybrids exhibited crossreactivity with peptides in which native serine75 or serine80 residues of GPMBP were substituted with either alanine75 (A75) or proline80 (P80) residues. These cross-reactive hybrids also possessed high levels of anti-RMBP reactivity. The remaining hybrids were unresponsive to the A75 and P80 substituted peptides and, with one exception, had relatively low levels of anti-RMBP reactivity. Unique reactivity patterns were also revealed by hybrid responses to peptides having modified C-terminal 84-86 residues. In summary, the contrasting fine specificities of different hybrids indicated that several distinct clones of T cells mediate the immune response of Lewis rats against the 68-86 region of GPMBP. Furthermore, heterogeneity in the hybrid response to "self" RMBP may reflect substantial differences in encephalitogenic potency of the T cell clones from which these hybrids were derived.