IDENTIFICATION OF AN N-TERMINALLY ACETYLATED ENCEPHALITOGENIC EPITOPEIN MYELIN PROTEOLIPID APOPROTEIN FOR THE LEWIS RAT

Proteolipid apoprotein (PLP) is a major component of the central nervo us system myelin. As such, it is capable of inducing experimental alle rgic encephalomyelitis (EAE) in many subhuman species. On the basis of a putative MHC class II binding motif in Lewis rats (RT-1B(1)) recent ly identified in our laboratory, the present study identifies one path ogenic T cell epitope of PLP for the Lewis rat, located in the area be tween amino acid residues 217 and 240. Four overlapping synthetic pept ides derived from this region were tested for their antigenicity and e ncephalitogenicity. Although the longer peptides could not induce EAE in the Lewis rats in their ''theoretically'' native form after immuniz ation, they were endowed with encephalitogenic ability when modified b y N-terminal acetylation. All animals immunized with N-acetylated pept ides PLP 217-233 and PLP 224-240 developed inflammation in the lower s pinal cord, but with very low incidence of clinical EAE (1 of 12). In contrast, none of the animals immunized with nonacetylated peptides de veloped either clinical or histologic EAE. Mild inflammation of the sp inal cord was also found in two of four rats immunized with N-acetylat ed peptide PLP 220-234. The animals immunized with the decapeptide, N- acetylated PLP 224-233, did not develop inflammation of the spinal cor d. Despite the low incidence of clinical disease, it was possible to g enerate vigorous T cell lines against all the peptides synthesized fro m this region of PLP. Both clinical and histologic EAE were adoptively transferred by T cells specific for N-acetylated forms of PLP 217-233 , PLP 220-234, and PLP 224-240, but not the T cells specific for N-ace tytated PLP 224-233, indicating that a PLP peptide longer than 10 amin o acid residues is required for encephalitogenicity. In vitro studies showed that acetylation of the N-terminal amino acid greatly enhanced both T cell proliferative responses and IL-2 production.