Kinetics of intracellular cAMP changes in BL cells treated by 38.13 MoAb. CD77⁺ Ramos, Daudi, and MUTU I cells, and CD77⁻ Namalwa, MUTU III, and VT500 cells were cultured with 38.13 anti-CD77 MoAb for various times, and cAMP concentrations were measured. Results are expressed in fold increase (left ordinate) of the basal cAMP level measured before stimulation (Ramos, 5.3; Daudi, 5.4; MUTU I, 2.3; Namalwa, 9; MUTU III, 3.2; VT500, 2.7 pmol/10⁶ cells). The effect of forskolin (50 μmol/L) on cAMP concentrations (fold increase on the right ordinate) in Ramos cells is also shown. Results are representative of seven independent experiments.