Immunofluorescent Staining: Fresh BALB/c spleen cells were activated by incubation for 72 hours with concanavalin A. Control cells were incubated in medium alone. At the end of 72 hours, the cells were harvested and stained with Rat anti-Mouse CD72-PE. Total cells were then gated and analyzed on a FACScan (TM) flow cytometer (BDIS, San Jose, CA). Amount Used: / = 0.1 ug/10e6 cells.