Leukocyte β2 integrins and CD44 are involved in interaction with SS RBCs. (A,B) Inhibition of PBMC interaction with epi-treated SS RBCs was performed as described in “Inhibition assays.” Results are presented as percentage of adherent PBMCs at a shear stress of 1 dyne/cm². (A) PBMC adhesion was measured after preincubation of PBMCs with anti-β2 integrin antibody followed by exposure to epi-treated SS RBCs. Error bars show SEM of 3 different experiments. *P < .001 compared with unstimulated PBMCs; **P < .001 compared with PBMCs preincubated with P3. (B) PBMC adhesion was measured after exposure to epi-treated SS RBCs, or epi-treated SS RBCs preincubated with sCD44 or sLW. Error bars show SEM of 4 different experiments. *P < .001 compared with unstimulated PBMCs; **P < .001 compared with PBMCs coincubated with SS RBCs preincubated with sLW, then treated with epi. (C) Phosphorylation of leukocyte CD44. Inorganic ³²P radiolabeled intact PBMCs were coincubated or not with sham-treated SS RBCs for 15 minutes or 30 minutes, or with epi-treated SS RBCs for 15 minutes or 30 minutes. Leukocyte CD44 was immunoprecipitated (IP) with anti-CD44 antibody or P3 as a control, as indicated. RBC CD44 was IP from sham-treated SS RBCs with anti-CD44 antibody. The cpm shown are quantitative data of the radioactive band at 85 kDa. One representative experiment is shown (n = 3). (D) Total immunoprecipitates (lanes 1-8) obtained using the same conditions as described in panel C but immunostained with A3D8 mAb against CD44.