Functional phenotype of resting and anergic T cells. The proliferative response of resting and anergic T cells to various doses of agonist peptide in the presence of irradiated autologous PBMCs was determined by [³H]-thymidine incorporation. The resting T cells proliferated in a dose-dependent manner, whereas anergic T cells were hyporesponsive upon stimulation with agonist peptide/PBMCs. However, both resting and anergic T cells proliferated upon stimulation with IL-2 or T-Stim. The results are expressed as mean counts per minute (cpm) for triplicate cultures and the data shown are representative of at least 3 independent experiments. (A) T-cell clone 7P.73, (B) T-cell line HA 308, (C) T-cell line Fel d 1 p4. (D) Irradiated anergic or resting Fel d 1 p4 T cells were coincubated with resting CFSE-labeled responder Fel d 1 p4 T cells in the presence of Ag-loaded APCs for 7 days. Proliferation of responder T cells was measured by flow cytometry. Panels i-ii show the extent of proliferation of restimulated resting responder or anergic T cells alone as controls. Panels iii-iv show the proliferation of restimulated responder T cells in the presence of irradiated resting or anergic T cells. Panels v-vi depict data from transwell experiments in which irradiated anergic or irradiated resting T cells were separated from the responder T-cell population by a transwell membrane (TW). Both the irradiated cells and the responders were incubated with Ag-loaded APCs. The right-hand peaks represent the parental population and generations of dividing cells are depicted leftwards along the x-axis. The results shown here are representative of 3 independent experiments.