Since RFs can be IFN-regulated, we used microarray analysis to assess whether the proviral and antiviral clusters might be selectively up- or down-regulated by either IFN-α or IFN-β, the two IFN subtypes previously used in HAM/TSP trials (Izumo et al., 1996; Oh et al., 2005). This evidence concerns the gene IFNA1 and tropical spastic paraparesis.