Decreased threshold for KIR transcription in the elderly. (A) CD158b/j⁻ CD4 and CD8 T cells from 20- to 30-year-old persons (n = 15; □) and 70- to 85-year-old persons (n = 12; ▩) were activated with CD3/CD28 beads and cultured in the absence or presence of 1 μM 5-Aza-dC as described in Figure 2. Cells were examined at indicated time points by flow cytometry. At 24 hours, CD158b/j expression in CD8 T cells from elderly persons was higher than in CD4⁺CD158b/j⁻ (P < .001) and in young CD158b/j⁻ CD8⁺ T cells (P = .001). No difference among any of the 5-Aza-dC–cultured groups was seen at 72 hours. (B) CD158b/j⁻ cells from 3 young and 3 elderly persons were cultured with anti-CD3 (0.1 ng/mL) and IL-15 (5 ng/mL); (C) cells from 7 young and 7 elderly persons were stimulated with anti-CD3, IL-15 (5 ng/mL), or IL-7 (10 ng/mL). CD158b/j expression was assayed after 7 days. Frequencies (B) and MFI (C) in young (□) and elderly (▩) persons are shown.