We observed a highly similar in vitro response (mean % increase ± SEM) to IFN-β for CD80, CD86 and another IFN-regulated (Rep et al., 1999; Van Weyenbergh et al., 2001) surface molecule (Fas/CD95, data not shown) in both HAM/TSP and MS patients. This evidence concerns the gene IFNB1 and myeloid sarcoma.