Binding of intercellular adhesion molecule-1 to the β₂-integrin leukocyte function associated antigen-1 (LFA-1) is known to induce cross-talk to the α₄β₁ integrin. Using different LFA-1 monoclonal antibodies, we have been able to study the requirement and mechanism of action for the cross-talk in considerable detail. LFA-1-activating antibodies and those inhibitory antibodies that signal to α₄β₁ induce phosphorylation of Thr-758 on the β₂-chain, which is followed by binding of 14-3-3 proteins and signaling through the G protein exchange factor Tiam1. This results in dephosphorylation of Thr-788/789 on the β₁-chain of α₄β₁ and loss of binding to its ligand vascular cell adhesion molecule-1. The results show that with LFA-1 antibodies, we can activate LFA-1 and inhibit α₄β₁, inhibit both LFA-1 and α₄β₁, inhibit LFA-1 but not α₄β₁, or not affect LFA-1 or α₄β₁. These findings are important for the understanding of integrin regulation and for the interpretation of the effect of integrin antibodies and their use in clinical applications.