Scheme for immune monitoring. Lymphocyte and monocyte populations were determined by forward scatter height (FSC-H) and side scatter height (SSC-H) levels (inside the central blue square). The former were gated as shown by the red ovals, and the latter were gated as shown by the green squares. (A) In the lymphocyte population, CD45⁺ cells were plotted according to CD2 (x-axis) and CD19 (y-axis) positivity, and these B cells were gated by quadrant (upper far left panel); also plotted are CD3⁺ (x-axis) and CD8⁺ (y-axis) cells, gated by quadrant (upper near left panel); CD16⁺ (x-axis) and CD56⁺ (y-axis) natural killer (NK) cells, gated by quadrant (upper near right panel); and CD4⁺ (x-axis) and CD25⁺ (y-axis) cells plotted as CD4⁺CD25^+dim-high cells gated by quadrant (upper far right panel). (B) In the monocyte population, CD45⁺ cells were plotted according to CD20 (x-axis) and CD11c (y-axis) positivity, and CD11c⁺ monocytes were gated by quadrant. (C) In the lymphocyte population, CD4⁺ cells were plotted according to FOXP3 (x-axis) and CD45RA (y-axis) positivity (lower left panel). Treg phenotypes of ATL cells were determined based on these data. CD4⁺ cells are also plotted according to CCR4 expression (x-axis) and CD25 (y-axis) positivity (lower middle panel). CD4 and CD25 double-positive cells are stained with anti-CCR4 monoclonal antibody (open graph) or isotype-control monoclonal antibody (filled graph) to show the level of CCR4 expression in ATL (CD4- and CD25-double positive) cells (lower right panel). (D) Within the lymphocyte population, CD4⁻, CD13⁻, and CD19⁻ cells were plotted according to HTLV-1 Tax tetramer (x-axis) and CD8 (y-axis) positivity (lower left panel) or CMV pp65 tetramer (x-axis) and CD8 (y-axis) positivity (lower right panel). These data were obtained from patient number 001.