Integrin binding is required for talin-1–dependent LFA-1 activation. K562 cells expressing wild-type α_L chain and wild-type or mutant β₂ chain were incubated with PMA (1μM) and then labeled with KIM127 mAb. Flow cytometry was used to measure the binding of KIM127. Data are the fold increase mean fluorescence intensity (MFI) ± SEM over control untreated cells (n = 3).