The percentage of double positive (perforin⁺ and surface marker⁺) lymphocytes (mean ± SE). CB lymphocytes (A, ▨;) and PBL from children (B, ▤), men (C, □), women (D, ▪), and elderly persons (E, ▥). Levels of significance (from P < .05 to P < .001) for: CD3 = (A) versus (B, C, D); (B) versus (D); (B, C, D) versus (E); CD4 = (B) versus (A, C, D, E); CD16 = (B) versus (A, C, D, E); (A) versus (E); (C) versus (D, E); (D) versus (E); CD8 = (A) versus (C, E); (B, C, D) versus (E); CD56 = (A) versus (C, E); (C) versus (D); (B, D) versus (E).