T- and B-cell nonresponsiveness to self-alphaB-crystallin in SJL mice prevents the induction of experimental allergic encephalomyelitis.

The myelin-associated stress protein alphaB-crystallin triggers strong proliferative responses and IFN-gamma production by human T cells and it is considered a candidate autoantigen in multiple sclerosis. In this study we examined the capacity of alphaB-crystallin or peptides derived thereof to induce experimental autoimmune encephalomyelitis (EAE) in SJL mice. Despite extensive efforts to induce EAE using active immunization with whole alphaB-crystallin, using adoptive transfer of lymphocytes or using peptide immunizations, no clinical or histological signs of EAE could be induced. SJL mice were unable to mount proliferative T-cell responses in vitro or delayed-type hypersensitivity responses in vivo to self-alphaB-crystallin. Also, immunization with self-alphaB-crystallin did not lead to any antibody response in SJL mice while bovine alphaB-crystallin triggered clear antibody responses within 1 week. Immunizations with alphaB-crystallin-derived peptides led to the activation of IL-4-producing Th2 cells and only a few IFN-gamma-producing Th1 cells. Peptide-specific T cells showed no cross-reactivity against whole alphaB-crystallin. The inability of SJL mice to mount proinflammatory T-cell responses against self-alphaB-crystallin readily explains the lack of EAE induction by immunization with whole protein or peptides derived from it. T- and B-cell nonresponsiveness is associated with constitutive expression of full-length alphaB-crystallin in both primary and secondary lymphoid organs in SJL mice, which is seen in other mammals as well, but not in humans.

Tolerance controls encephalitogenicity of alphaB-crystallin in the Lewis rat.

The myelin-associated protein, alphaB-crystallin, is considered a candidate autoantigen in multiple sclerosis (MS). In the present study, we examined the potential of alphaB-crystallin to induce experimental autoimmune encephalomyelitis (EAE) in Lewis rats. Attempts to induce EAE with either bovine, rat or murine alphaB-crystallin or alphaB-crystallin peptides consistently failed. Immunization with either autologous rat or murine alphaB-crystallin did not trigger any antigen-specific T cell response. Immunization with bovine alphaB-crystallin or a synthetic peptide representing the cryptic epitope 49-64 did trigger T cell responses but these failed to crossreact with autologous rat alphaB-crystallin. Examination of lymphoid tissues of the Lewis rat revealed constitutive expression of alphaB-crystallin in thymus, spleen, and peripheral lymphocytes. Our data show that in Lewis rats, constitutive lymphoid expression of alphaB-crystallin is associated with a state of nonresponsiveness to autologous alphaB-crystallin that effectively controls the development of EAE in response to this myelin antigen.

T cells discriminate between differentially phosphorylated forms of alphaB-crystallin, a major central nervous system myelin antigen.

Factors such as developmental stage or physiological and infectious stress may change patterns of post-translational protein modification. In order to determine whether such regulated types of modification may influence T cell responsiveness to self proteins we examined the T cell response of SJL (H-2s) mice to alphaB-crystallin, a small heat shock protein that can exist in differentially phosphorylated forms. Epitope mapping revealed the presence of two T cell epitopes that are presented by I-As. One major epitope including residues 41-56 contains an amino acid residue (Ser45) that can be phosphorylated as the result of aging or stress. Accordingly, T cells from SJL mice discriminate between preparations of alphaB-crystallin that differ in their extent of phosphorylation at the level of whole protein as well as at the level of determinant-specific responses. Phosphorylation at Ser45 does not prevent binding of the peptide 41-56 to I-As and computer-assisted modelling of the peptide-MHC complex suggests that the phosphate group of the bound peptide extends outwards from the peptide-binding cleft and may thus be available for direct contact with TCR. Together, our data provide evidence that stress-inducible phosphorylation of alphaB-crystallin creates neo-determinants for T cells and, therefore, may contribute to the breakdown of peripheral tolerance to this self protein.