The frequency of pro-inflammatory cytokine positive cells within the OX40+CD4+ and Tax+CD4+ populations from HAM/TSP patients are significantly higher than OX40-CD4+ and Tax-CD4+ T cells, respectively (p < 0.001, Student's t- test) (Figure 2F and Table 1). This evidence concerns the gene TNFRSF4 and tropical spastic paraparesis.