Increased severity of experimental autoimmune encephalomyelitis in rats tolerized as adults but not neonatally to a protective TCR V beta 8 CDR2 idiotope.

The ability of synthetic V region peptides to induce regulatory T cells and Abs in rodents and humans provides clear evidence that these idiotopes do not naturally induce tolerance. In this study, we investigated the ability of TCR V beta 8.2 peptides to experimentally induce specific T cell tolerance, as measured by loss of Ag-specific proliferation and delayed-type hypersensitivity responses, and by increased susceptibility to experimental autoimmune encephalomyelitis (EAE). We found that both neonatal and adult exposure to V beta 8.2-39-59 or V beta 8-44-54 peptides could induce efficient T cell tolerance, resulting in a significant inhibition of peptide-specific proliferative responses. In addition, neonatal tolerance resulted in a partial reduction in delayed-type hypersensitivity response and an inability to vaccinate against EAE after adult immunization with the tolerizing peptide. We further evaluated the contribution of naturally induced TCR-specific responses to EAE resistance induced by challenging neonatally or adult tolerized rats with myelin basic protein in adjuvant. The clinical course of EAE was not significantly altered in rats tolerized neonatally to V beta 8.2 peptides, but both the severity and incidence of mortality from EAE was increased in rats tolerized as adults with V beta 8.2 peptides conjugated to syngeneic splenocytes. These results demonstrate that V beta 8.2 peptides are tolerogenic as well as immunogenic. Moreover, the observation of different effects of neonatal vs adult tolerization on the course of EAE suggests either the emergence of additional protective idiotopes after neonatal tolerization and/or mechanistic differences in the two tolerance-inducing protocols. Most importantly, the enhancement of clinical EAE in rats tolerized as adults with V beta 8.2 peptides provides evidence for an innate regulatory role of the CDR2 idiotope in recovery from EAE.

Epitope and functional specificity of peripheral tolerance induction in experimental autoimmune encephalomyelitis in adult Lewis rats.

Intravenous treatment of Lewis rats with neuroantigen-coupled splenocytes 7 days before the induction of experimental autoimmune encephalomyelitis with guinea pig myelin basic protein (GP-MBP) resulted in a significant reduction of both the incidence and severity of clinical disease. To test the epitope and functional specificities of the unresponsiveness, splenocytes (SP) coupled with the major encephalitogenic MBP determinant, GP-68-86, were compared with those coupled with intact GP-MBP for the ability to down-regulate clinical disease and Ag-specific T cell responses (proliferation, cytokine production, and delayed-type hypersensitivity) in animals primed with either intact GP-MBP/CFA or GP-68-86/CFA. GP-MBP-SP and GP-68-86-SP were equally efficient at significantly inhibiting clinical disease in animals primed with GP-68-86/CFA. In contrast, tolerization with intact GP-MBP-SP was significantly more efficient than that with GP-68-86-SP at reducing disease incidence and severity in GP-MBP/CFA-primed animals, which indicates a role for secondary (cryptic) encephalitogenic epitopes in GP-MBP-induced disease. By testing a panel of GP-68-86 peptides that contained conservative amino acid substitutions at either position 75 (A75) or 80 (P80) or at both, residues that previously had been shown to be TCR contact residues, for their ability to inhibit experimental autoimmune encephalomyelitis induction, were assessed for the fine specificity of tolerance induction. None of the substituted peptides were capable of affecting the course of paralytic disease that had been induced by sensitization with the native GP-68-86 epitope, but all significantly reduced a milder form of the disease that had been produced by priming with the (A75,P80) 68-86 substituted peptide. With regard to the functional specificity of tolerance induction, lymph node T cells derived from either GP-MBP-SP- or GP-68-86-SP-treated animals exhibited a marked reduction in both proliferation and production of Th1-derived cytokines (IL-2, IFN-gamma, and lymphotoxin/TNF-alpha) in response to either GP-MBP or GP-68-86 in culture. In contrast, no consistent significant differences in delayed-type hypersensitivity responses were observed in any of the experimental groups relative to controls. Histologic examination of central nervous system tissues from the tolerant and control groups revealed significantly reduced, but still demonstrable, levels of perivascular infiltration even in asymptomatic animals.

Differential recognition of sequences within the encephalitogenic region of myelin basic protein capable of eliciting cell-mediated immune responses in experimental autoimmune encephalomyelitis.

The fine specificity of myelin basic protein (MBP) epitopes capable of eliciting in vivo delayed-type hypersensitivity responses in Lewis rats with experimental autoimmune encephalomyelitis (EAE) was compared to those eliciting in vitro antigen-specific T cell proliferation and augmentation of disease transfer. Utilizing a panel of synthetic peptides with sequences representing the 68-86 region of guinea pig (GP-) or bovine myelin basic protein (B-MBP), animals were primed with one species of peptide and subsequently challenged with either the same peptide or peptides with truncations or substitutions representative of the other species of MBP. In regard to minimal length sequences capable of eliciting delayed-type hypersensitivity (DTH), rats primed with GP-MBP and complete Freund's adjuvant (CFA) exhibited a hierarchical pattern of responsiveness to challenge with a series of truncated peptides, ranking as follows: GP-68-86 > GP-72-86 > GP-68-84 > > GP-75-86 = no activity. This response pattern corresponds to that previously reported for T cell proliferation and activation for disease transfer. Furthermore, a comparison of these T cell-mediated immune parameters, as elicited by the substituted peptides, revealed the response patterns of DTH reactivity to be similar to that previously described for in vitro T cell proliferation with significant DTH responses generated only by the peptide species for which the animal was primed. In contrast, a cross-reactive pattern of recognition was observed in cells mediating disease transfer, with all four 68-86 sequences capable of augmenting activation for adoptive transfer of disease, regardless of the peptide species for which the animal was primed.(ABSTRACT TRUNCATED AT 250 WORDS)