In addition, soluble factors such as interferon-α/β (IFN-α/β), released as a result of infection, appear to be involved in the induction of MHC class I on CNS cells (Njenga et al., 1997b) . Of interest, electrically silent neurons upregulate MHC class I molecules on their surface (Neumann et al., 1995) , thus predisposing them to cytotoxic attack.