Tax expression in CD4+ lymphocytes from HTLV-I infected individuals. The proportion of CD4+ cells expressing the viral protein Tax after 18 h ex vivo incubation in the absence of CD8+ cells was measured by flow cytometry. Tax expression was significantly higher in lymphocytes from HAM/TSP patients than from ACs of comparable proviral load (ANOVA, two tailed test p = 0.014. Permutation test two-tailed test p = 0.017). This result was robust to removal of outliers: the P value either remained unchanged or decreased on removal of outliers.