Separate and cognate help lead to qualitatively and quantitatively different H60-specific memory CD8 T-cell responses. (A) B6 mice that had been immunized with male H60 cells were boosted with male H60 cells or a mixture of male B6 and female H60 cells. PBLs from the immunized mice (5 mice per group) were stained periodically with H60-tetramer-PE, anti–CD8-APC, and anti–CD11a-FITC, and the percentage of H60-tetramer⁺ CD11a⁺ CD8 T cells was plotted. The FACs results from day 7 postsecondary immunization are shown (gated for CD8⁺ cells). The data are taken from 1 of 5 independent experiments. (B) Female B6 mice were adoptively transferred with CD8 T cells purified from female Ly5.1 (CD45.1⁺) mice that had been immunized with male H60 cells 40 days earlier and then challenged with male H60 cells or a mixture of male B6 and female H60 cells. PBLs from the challenged adoptive hosts were stained with H60-tetramer-PE, anti–CD8-APC, and anti–CD45.1-FITC and flow cytometric analysis was performed after gating for the CD45.1⁺ cells. The data are representative of 2 independent experiments.