Figure 4E demonstrates that the amount of SAP expression in Tax11-19 tetramer+ CD8+ T cells was significantly correlated with HTLV-I proviral DNA loads in PBMCs (P = 0.0401, R2 = 0.4746) and the frequency of Tax11-19 tetramer+ CD8+ T cells in HTLV-I-infected individuals (P = 0.0062, R2 = 0.6811). These results suggest that expansion of HTLV-I-specific CD8+ T cells particularly in patients with HAM/TSP is associated with the expression of SAP and can distinguish patients with neurologic disease from HTLV-I infected asymptomatic carriers. This evidence concerns the gene SH2D1A and tropical spastic paraparesis.