As we did not detect upregulation of these genes in cortical neurons from MS patient autopsy tissue, it is possible that they are only transiently upregulated (as we have noted in response to IFN-γ signaling; ref. 40), that these mRNA molecules are transported into the axon and only translated locally at the site of peptide presentation (67), or that neurons are limited to TAP1/2-independent MHC class I peptide presentation mechanisms (68, 69). This evidence concerns the gene IFNG and myeloid sarcoma.