Peripheral blood T-cell counts in frequent plateletpheresis donors. Cell counts are plotted for the 3 donor groups. (A) CD4⁺ T-cell counts. The horizontal dotted line indicates 200 cells/µL. (B) CD8⁺ T-cell counts. The horizontal dotted line indicates the lower limit of normal. Blue symbols indicate volunteers who donated 20 to 24 times in a 365-day period during the past 20 years. (C) CD4⁺ T-cell counts by total plateletpheresis sessions. (D) CD8⁺ T-cell counts by total sessions. The vertical dotted line indicates 50 donations.