Proliferation of PBLs from IM subjects in response to IL-2 or IL-15. CFSE-labeled PBLs prepared from one IM subject (IM02) were cultivated for 6 days with or without anti-CD3 mAbs in the absence or presence of various concentrations of IL-15 (1-100 ng/mL) or IL-2 (100 IU/mL). The percentage of proliferating cells was analyzed by flow cytometry measurements of the dilution of CFSE on day 6 in CD4+ or CD4− T-cell fractions after staining with an anti–CD4-PE mAb. Seven successive generations of lymphocytes were observed, and the indicated percentages represent the proliferating cells in the CD4− cell fraction for each cell treatment. Data are representative of 4 identical experiments. Similar results were obtained with T cells from healthy subjects (data not shown).