Critical requirement for aspartic acid at position 82 of myelin basic protein 73-86 for recruitment of V beta 8.2(+) T cells and encephalitogenicity in the Lewis rat

We synthesized single amino acid-substituted peptide analogues of guinea pi g myelin basic protein (MBP) 73-86 to study the importance of aspartic acid at residue 82 (QKSQRSQDENPV), which previous reports have suggested is a c ritical TCR contact residue. Whereas the wild-type 73-86 peptide elicited s evere experimental autoimmune encephalomyelitis (EAE) in the Lewis rat, non e of the peptide analogues with substitutions at position 82 were capable o f inducing EAE, The inability to cause EAE was not due to a failure to bind MHC or to elicit T cell proliferation and cytokine secretion, T cells spec ific for MBP73-86 did not cross-react with any of the analogues tested, fur ther indicating the importance of this residue in T cell responses to 73-86 , Analysis by flow cytometry showed that only the wild-type 73-86 peptide w as capable of recruiting V beta 8.2(+) T cells, which have been shown previ ously to be important for disease induction. Reduced expression of the V be ta 8.2 TCR was also seen in Lewis rats protected from EAE by communication of MBP73-86 with 73-86(82D --> A), despite an increase in cytokine producti on when both peptides were present during in vitro culture. The data indica te that aspartic acid 82 is a critical TCR contact residue and is required for the recruitment of V beta 8.2(+) T cells and the encephalitogenic activ ity of MBP73-86.