Interestingly, PBMC from the three asymptomatic carriers analyzed, PH1614, PH1619 and PH1621, did not show any positivity for HBZ (Fig 3A), although they expressed Tax-1 in a small but distinctive proportion of cells (11%, 1% and 6%, respectively, Table 1) with a preferential, although not exclusive, nuclear localization (Fig 3B). Taken together, these results establish for the first time a striking difference in the subcellular localization of HBZ protein in HAM/TSP patients as compared to ATL patients, showing the unprecedented exclusive cytoplasmic localization of HBZ in HAM/TSP patients. This evidence concerns the gene HBZ and tropical spastic paraparesis.