Given the hypothesized role of KP metabolism in the mechanism underlying the depressive side-effects associated with IFN-α-based immunotherapy (Bonaccorso et al., 2002a), KP activation may be similarly involved in the depressive side-effects often reported for MS patients undergoing IFN-β treatment (Goeb et al., 2006). This evidence concerns the gene IFNA1 and myeloid sarcoma.