With regard to HTLV-1 genes other than the previously reported genes, we examined the expressions of HTLV-1 bZIP factor (HBZ) and tax gene by ISH, which showed that both genes expressed in infiltrating MNCs and SGECs from HAM-SS patients and a patient with adult T-cell leukemia (ATL), although the expression of tax gene was dominant in MNCs of the HAM-SS patients [127] (Figure 1A,B). This evidence concerns the gene HBZ and tropical spastic paraparesis.