Cryptic MBP epitope 1-20 is inducing autoimmune anterior uveitis without EAE in Lewis rats

Lewis rats immunized with myelin basic protein (MBP) developed experimental autoimmune encephalomyelitis (EAE) and associated anterior uveitis (AU). Although several cryptic epitopes of MBP have strong encephalitogenic and uveitogenic properties, the peptide corresponding to the MBP residues 1-20 was uniquely capable of inducing AU without EAE. In this study, we showed that acetylation of the N-terminal amino acid did not produce encephalitogenicity, did not enhance uveitogenicity, and did not improve T cell proliferation in Lewis rats. The cytokine production profile induced by MBP_1-20 immunization was consistent with a Th1 response. In MBP-injected rats and in peptide-injected rats, the frequency of the IFN-γ-secreting cells in MBP_69-89-stimulated T cells was significantly higher than the frequency of IFN-γ-secreting cells in MBP_1-20-stimulated T cells. However, similar numbers of IFN-γ-producing specific cells were found in the eyes of MBP_69-89 and MBP_1-20 immunized rats. In these rats, the iris-infiltrating cells consisted of a much higher percentage of CD4⁺ T cells expressing L-selectin (CD62L) than did those cells found in the spinal cord. The results demonstrate that MBP_1-20 is immunogenic and uveitogenic, although it induced only weak proliferation and weak Th1 reaction. The fact that T cells with the same specificity have different effects on target organs suggested that, in the eye and spinal cord, a distinct mechanism might mediate the recruitment of cells to these organs.