Platelet-associated factor XIII as a marker of platelet activation in patients with peripheral vascular disease.

In the past several years, monoclonal antibodies have been developed that distinguish between resting and activated platelets in vitro. These antibodies recognize epitopes expressed on membrane proteins or soluble proteins, such as factor XIIIa and thrombospondin, that bind only to activated platelets. We have used fluorescence flow cytometry to determine whether three such antibodies can detect platelet activation in patients with severe peripheral vascular disease (PVD). Using two activation-specific monoclonal antibodies and a polyclonal antiserum to factor XIII a-chain, we have examined the platelets from PVD patients, age-matched control subjects who were free of detectable PVD, and unmatched control subjects. Cells analyzed as platelets were identified by their light-scatter profile and their reactivity with monoclonal anti-glycoprotein Ib. The platelets of patients with PVD showed no increase in binding of activation-dependent 1B3 (directed against a 180-kD membrane protein) compared with age-matched control subjects (p = 0.780). Similarly, there was no difference between PVD patients and control subjects in activation-dependent CD63 expression. Conversely, the binding of anti-factor XIII a-chain was significantly higher than in the control groups (p < 0.001). These data suggest that the detection of soluble factors that bind to activated but not resting platelets may be of use in the detection of pathological in vivo platelet activation.