LFA-1– and VLA-4–mediated adhesion of PBL from a healthy donor both measured with the fluorescent beads and the plate adhesion assay. Binding of ICAM-1–coated fluorescent beads by PBL after stimulation with PMA (A) and in the presence of anti–LFA-1 blocking antibody NKI-L15 (B). (C and D) Comparison of the adhesion as measured with both assays. Adhesion was measured without any stimulus and after stimulation with PMA or an activating anti-β2 (KIM185) or anti-β1 (TS2/16) MoAb. The specificity was determined by measuring adhesion in the presence of blocking anti–LFA-1 (NKI-L15) or anti–VLA-4 (HP2/1) MoAb.