Phenotype and proliferative ability of regulatory DC-maintained long-lived CD4 T cells. (A) Naive CD4⁺ T cells, effector CD4⁺ T cells, and the long-lived CD4 T cells maintained by regulatory DCs for > 30 days (Longeval CD4⁺ T cells) were stained for the indicated markers and analyzed by flow cytometry. Slim solid line, background staining. Shaded histograms, specific antibodies. (B) Long-lived CD4 T cells or naive CD4 T cells were stimulated with mDCs and 200nM OVA_323-339, and viable CD4⁺ T cells were counted by flow cytometry on days 1, 2, and 3. (C) The long-lived CD4 T cells or naive CD4 T cells were labeled with 5μM CFSE and then cultured with mDCs in the presence of 200nM OVA_323-339. Viable CD4⁺ T cells were then gated for analyzing the CFSE content of CD4 T cells by flow cytometry on days 1, 2, and 3. Numbers in the histograms indicate the geometric mean fluorescence of the test samples. **P < .01. Similar results were obtained in at least 3 independent experiments.