Flow cytometric analysis of human peripheral blood mononuclear cells, untreated (left column) or treated with anti-CD3 plus anti-CD28 (10 μg/ml, 72 hr; right column), using Granzyme B (D2H2F) Rabbit mAb (top row) or concentration-matched Rabbit (DA1E) mAb IgG XP<sup>®</sup> Isotype Control #3900 (bottom row), and co-stained with a CD8 Antibody. Anti-rabbit IgG (H+L), F(ab')<sub>2</sub> Fragment (Alexa Fluor<sup>®</sup> 488 Conjugate) #4412 was used as a secondary antibody.