Increased intracellular cAMP induces SS RBC adhesion to EC-RF24 cells. (A) SS RBCs were sham treated or treated with 0.025 to 0.2 mM IBMX and tested for adhesion to EC-RF24 cells at different shear stresses. (B) Sham-treated or IBMX-treated normal RBCs were tested for their ability to adhere to EC-RF24 cells. Each graph is representative of 2 different experiments. (C) SS RBCs were sham treated (n = 8) or treated with 0.2 mM IBMX (n = 5), 0.2 mM IBMX + 176 μM db-cAMP (n = 9), or 0.2 mM IBMX + 176 μM Br-cAMP (n = 9). As controls, EC-RF24 cells were incubated with 0.2 mM IBMX + 176 μM db-cAMP (n = 3) or with the supernatant obtained from the last wash of SS RBCs treated with 0.2 mM IBMX + 176 μM db-cAMP (n = 3). Adhesion was assayed at a shear stress of 2 dynes/cm². Error bars in panel C show standard deviation (SD). ^*P < .0002 compared with sham-treated SS RBCs; ^**P < .002 compared with SS RBCs + IBMX; and ^***P < .0002 compared with SS RBCs + IBMX.