The accumulation of GrB⁺CD8⁺ T cells and 4-1BBL⁺ B cells is evolutionarily conserved in old mammals. (A,C) In rhesus macaques (PB) and (B,D) mice (spleen). Shown is the mean ± SEM of GrB⁺ within CD8⁺ T cells in macaques (A, %) and in mice (B, representative dot plots, %, left panel; and absolute #, right panel) and 4-1BBL⁺ B cells in gated macaque CD20⁺ cells (MFI, C) and splenic murine CD19⁺ cells (B, representative dot plots, %, left panel; and absolute #, right panel). The increase of 4-1BBL⁺ B cells and GrB⁺CD8⁺ T cells in old mice is lost after regeneration of B cells induced with anti-CD20 Ab treatment (B,D, Old-restored). Control old mice (Old-IgG) were treated with isotype control Ab. (B,D) Representative results of 5-mice-per-group experiment independently reproduced 4 times. No correlation between age and IFNγ⁺CD8⁺ T cells was detected (A).