Dose response of ATP- and BzATP-induced shedding of CD23 and L-selectin. B-CLL lymphocytes were incubated with the indicated concentration of ATP (A) or BzATP (B) for 7 minutes before labeling with anti-CD23 (○) or for 1.5 minutes before labeling with anti–L-selectin (•). Results are expressed as mean percentage of initial expression ±SEM (n = 3).