IL-2 is a potent inducer of apoptosis in unprotected but not protected γδ-T cells.

Unprotected and protected PBMC cultures were initiated on day 0, as described above. All cultures received OKT3 and IL-2 after 24 hours (day 1 mitogenic signals). On day 7, γδ-T cells in both unprotected and protected cultures were analyzed for apoptosis, as measured by the uptake of annexin V-FITC and PI (upper dot plots, day 7). The percentages of viable γδ-T cells (annexin⁻/PI⁻) and apoptotic γδ-T cells (annexin⁺/PI⁻) in each dot plot are indicated in the corresponding quadrants. Subsequently, IL-2 (100 U/mL) was added to equivalent numbers of cells from both protected and unprotected PBMC cultures. After overnight incubation, apoptosis in γδ-T cells was once again determined (middle dot plots, day 8, IL-2). Agonistic mouse antihuman CD95/Fas mAb CH11 (mouse IgM) was included in identical cultures as a positive control (lower dot plots, day 8, CH-11). Day 8 cultures (protected and unprotected) to which PBS alone or to which mouse IgM isotype control for CH11 was added were essentially unchanged with respect to apoptosis when compared to day 7 cultures (not shown). Addition of IL-2 had a minimal effect on apoptosis detected in αβ-T cells within either protected or unprotected cultures (not shown). Results are representative of experiments performed using materials obtained from at least 2 different persons.