Association of Tax and 4-1BB expression on CD4⁺ and CD8⁺ lymphocytes from HTLV-1–infected patients. (A) PBMCs were cultivated in the presence of concanamycin A for 18 hours. Subsequently, they were stained for CD4, Tax, and 4-1BB and analyzed by flow cytometry. Cells were gated on the CD4⁺ T-cell population. One representative dot plot is shown. (B) Expression of 4-1BB in the Tax-positive (•) and Tax-negative (▴) CD4⁺ T cells was compared using a 2-tailed Mann-Whitney test. PBMCs from 19 subjects were analyzed by flow cytometry as exemplified in panel A. Horizontal bars indicate the median. (C) Expression of 4-1BB in the Tax-positive (•) and Tax-negative (▴) CD8⁺ T cells from 17 subjects was compared in analogy to panel B. Horizontal bars indicate the median.