Fresh BALB/c spleen cells were activated by incubation for 20 hours with PMA + ionomycin, then stained with either hamster IgG-FITC (as an isotype control) or Cd69 monoclonal antibody, clone H1.2F3 (FITC) (Cat # MAB5742). Large, activated cells were then gated and analyzed on a FACScan™ flow cytometer (BDIS, San Jose, CA).