Cytoskeletal regulation couples LFA-1 conformational changes to receptor lateral mobility and clustering

The alpha(L)beta(2) integrin (leukocyte function-associated antigen-1 [LFA-1]) is regulated to engage and maintain T cell adhesion. Conformational changes in the receptor are associated with changes in receptor-ligand affinity and are necessary for firm adhesion. Less well understood is the relationship between receptor conformation and the regulation of its lateral mobility. We have used fluorescence photobleaching recovery and single-particle tracking to measure the lateral mobility of specific conformations of LFA-1. These measurements show that different receptor conformations have distinct diffusion profiles and that these profiles vary according to the activation state of the cell. Notably, a high-affinity conformation of LFA-1 is mobile on resting cells but immobile on phorbol-12-myristate-13-acetate-activated cells. This activation-induced immobilization is prevented by a calpain inhibitor and by an allosteric LFA-1 inhibitor. Our results suggest that current models of LFA-1 regulation are incomplete and that LFA-1 confinement by cytoskeletal attachment regulates cell adhesion both negatively and positively.