Leucocyte migration inhibition factor (LIF) and antithrombin III (AT III)

The activity of LIF, produced in vitro by sensitized lymphocytes exposed to the appropriate antigens, is readily abolished in the simultaneous presence of heparin and thrombin. Heparin or thrombin alone are without significant effects. Adding AT III together with heparin and thrombin restores the LIF activity. We suggest that the migrating leucocytes on their cell membranes have receptors, composed of AT III-like molecules, which are blocked or destroyed, by forming complexes with heparin and thrombin. However, the heparin-thrombin complex will preferentially interact with AT III added to the culture medium, thus leaving the cellular receptors free to interact with LIF.