In MS naïve T cells are found in the cerebrospinal fluid during relapses [26] and the experiments from Brabb et al. support a possible function for the development of tolerance [9]: Using MBP (myelin basic protein)-recognizing T-cell receptor transgenic mice, they showed that naïve MBP-specific T cells isolated from the brain did not show any reactivity for MBP in vitro. Here, MBP is linked to myeloid sarcoma.