The cytosolic protein Talin induces an intermediate affinity integrin αLβ2

The integrin alpha(L)beta(2) mediates leukocyte adhesion and migration that are required for a functional immune system. It is known that inside-out signaling triggers alpha(L)beta(2) conformational changes, which affect its ligand-binding affinity. At least three alpha(L)beta(2) affinity states (low, intermediate, and high) were described. The cytosolic protein talin connects alpha(L)beta(2) to the actin filament. The talin head domain is also known to activate alpha(L)beta(2) ligand binding. However, it remains to be determined whether talin promotes an intermediate or high affinity alpha(L)beta(2). In this study using transfectants and T cells, we showed that talin induced an intermediate affinity alpha(L)beta(2) that adhered constitutively to its ligand intercellular adhesion molecule (ICAM)-1 but not ICAM-3. Adhesion to ICAM-3 was induced when an additional exogenous activating agent was included. Similar profiles were observed with soluble ICAMs. In addition, the intermediate affinity alpha(L)beta(2) induced by talin allowed adhesion and migration of T cells on immobilized ICAMs.