In Situ Tolerance within the Central Nervous System as a Mechanism for Preventing Autoimmunity

Brabb, Thea; von Dassow, Peter; Ordonez, Nadia; Schnabel, Bryan; Duke, Blythe; Goverman, Joan

In Situ Tolerance within the CNS CNS of healthy, older transgenic mice than in younger mice was inconsistent with the fact that the incidence of spontaneous EAE is significantly higher in younger rather than older mice. Therefore, we investigated the possibility that, in contrast to activated T cells, naive MBP-specific transgenic T cells entering the CNS undergo tolerance in situ and become unresponsive to MBP. CNS T cells isolated from 14-17 healthy MBP TCR1 transgenic mice were pooled and cultured in vitro with MBP Ac1-11. T cell-depleted splenocytes from wild-type mice were added as APCs. V ␣ 2 ϩ T cells isolated from the CNS of MBP TCR1 transgenic mice did not proliferate in response to antigen (Fig. 4, A and B , P ϭ 0.004). In contrast, V ␣ 2 ϩ T cells from LNs of the same animals plated at the same density as the CNS T cells proliferated robustly in response to MBP Ac1-11. CNS T cells isolated from MBP TCR2 transgenic mice also did not proliferate in response to antigen, whereas LN T cells proliferated strongly (Fig. 4 B) . To determine whether the induction of nonresponsiveness in T cells within the CNS was unique to T cells specific for MBP, two different MHC class II-restricted TCR transgenic mouse models specific for non-CNS antigens were analyzed using the same experimental protocol. Both CNS and LN T cells harvested from TEa TCR transgenic mice specific for the MHC class II E␣ peptide and DO11.10 TCR transgenic mice specific for ovalbumin proliferated equally when stimulated with E␣ peptide and Ova peptide, respectively, in vitro (Fig. 4 B) . Thus, nonresponsiveness of T cells from the CNS was observed only when the T cells were specific for a CNS antigen. Previous studies of tolerance to tissue-specific antigens have implicated draining LNs as the site for induction of T cell tolerance. Therefore, we investigated the possibility that nonresponsiveness may be induced in the MBP-specific T cells by presentation of MBP epitopes in the cervical LNs that are believed to drain the CNS (29, 30) . In the experiments in Fig. 4 B, T cells from multiple peripheral LNs draining different tissues were pooled together such that nonresponsiveness in the cervical LNs might not have been detected. Fig. 4 C compares the proliferative responses to MBP Ac1-11 of V ␣ 2 ϩ T cells isolated from the cervical and inguinal LNs of MBP TCR1 transgenic mice. T cells from both types of LNs proliferated strongly to MBP peptide, supporting the idea that induction of tolerance in MBPspecific T cells occurs within the CNS itself.