AN INHIBITOR FROM THE ARGASID TICK ORNITHODOROS-MOUBATA OF CELL-ADHESION TO COLLAGEN

An inhibitor of the adhesion of human platelets to collagen was identi fied in soluble extracts of the soft tick Ornithodoros Moubata and pur ified by four chromatographic steps. The isolated inhibitor, TAI (Tick Adhesion Inhibitor), is a similar to 15-kDa protein that completely b locks the adhesion of platelets to collagen-coated microtiter plates w ith an IC50 of 8 nM. In the same concentration range it does not inhib it collagen-induced platelet aggregation or platelet adhesion to fibri nogen and has a partial inhibitory effect on platelet adhesion to fibr onectin. TAI also blocks the adhesion of human endothelial cells to co llagen, thus its inhibitory effect is not limited to platelets. TAI co mpetes for the binding to platelets of a radiolabeled monoclonal antib ody against the platelet glycoprotein Ia-IIa integrin complex. Based o n its selective activity and small size, TAI is a promising new molecu le for exploring cell-collagen interactions. (C) 1995 Academic Press, Inc.