RECIRCULATED NORMAL PLATELETS ADHERE TO SURFACES COATED WITH PLASMA FROM PATIENTS WITH IMMUNE THROMBOCYTOPENIA

Immune thrombocytopenic purpura (ITP) patients have characteristic ant i-platelet antibodies in their circulation. To assess the interaction between such antibodies adhering on to a non-physiological surface and human platelets, normal anticoagulated blood was perfused over ITP pa tient plasma-coated surfaces in a parallel plate flow chamber. At 300 s(-1), platelet adhesion to patient plasma-coated glass coverslips (24 .0 +/- 10%) was significantly higher than the adhesion to normal plasm a-coated surfaces (9.8 +/- 7%). When perfused at 1300 s(-1), the adhes ion to patient plasma- (5.1 +/- 1.3%) and to normal plasma- (2.5 +/- 1 .2%) coated coverslips were significantly weaker. Furthermore, patient platelet binding depended on simultaneous contributions by antibodies and fibrinogen present on the plasma-coated surface, since adherence was antagonized both by normal immunoglobulins added to the perfusate, as well as by the anti-GPIIb/IIIa monoclonal antibody 16N7C2, which c ompetes with fibrinogen for binding to its receptor on the platelet. A ccordingly, platelet adhesion was only observed to coverslips coated w ith the plasma but not the serum of ITP patients. Hence, perfusion of normal platelets over surfaces coated with ITP patient plasma enables a functional assessment of the presence in this plasma of anti-platele t antibodies.