The frequency of perforin expressing cells (mean ± SE) in the various lymphocyte phenotypes in CB lymphocytes (A, ▨;) and PBL from children (B, ▤), men (C, □), women (D, ▪), and elderly persons (E, ▥). Levels of significance (from P < .05 toP < .001) for: CD3 = (A) versus (E); (B) versus (C, D, E); (C, D) versus (E); CD4 = (B) versus (A, C, D, E). CD8 = (A) versus (C, E); (B) versus (E); (C, D) versus (E); CD16 = (A) versus (B); (B) versus (C, D, E); (C, D) versus (E). CD56 = (A) versus (B, C, E); (B) versus (D, E); (C) versus (D, E); (D) versus (E).