Objective      To investigate the effect of anti-inflammatory and anticoagulant tick anticoagulant peptide (TAP)-staphylococcal superantigen-like protein 5 (SSL5) fusion protein on human platelet functions.       Methods      Gel-filtered platelets (GFP) were prepared from human platelet-rich plasma (PRP). Flow cytometry (FCM) was applied for the binding assay of TAP-SSL5 fusion protein and mouse anti-human CD42b (GPIbα) monoclonal antibody (HIP1) to platelets. Both the expression of P-selectin on the platelet surface and the PAC-1 binding to the platelets were assayed by FCM. Platelet aggregation induced by TAP-SSL5 fusion protein was analyzed by whole blood impedance platelet aggregometry. The mouse tail bleeding time was recorded after venous injection of TAP-SSL5 fusion protein to evaluate the bleeding risk of TAP-SSL5 fusion protein.       Results      TAP-SSL5 fusion protein could bind to platelets and competitively inhibit HIP1 to bind to platelets

indicating that TAP-SSL5 fusion protein could bind to GPIbα on platelets and inhibit the interaction between GPIbα and von Willebrand Factor (vWF). A high concentration of TAP-SSL5 fusion protein could also activate platelets

and 30 mg/L TAP-SSL5 fusion protein resulted in 90.4% P-selectin positive platelets and 66.3% PAC-1 positive platelets. TAP-SSL5 fusion protein at high concentrations promoted platelets aggregation as well (10 and 30 mg/kg). TAP-SSL5 fusion protein (10 mg/kg) significantly prolonged the mouse tail bleeding time. The mouse tail bleeding time was prolonged to (753.6±127.3)s

which was significantly longer than that of the mice without the injection [(647.1±33.7)s

P0.01]. However

the tail bleeding time of the conventional dose group (3 mg/kg) was (612.8±79.1)s

which was not significantly different from that of the control group (P0.05).       Conclusion      TAP-SSL5 fusion protein keeps the ability of SSL5 binding to GPIbα on platelets

which may improve the anti-thrombosis function of TAP-SSL5 fusion protein and also lead to the prolongation of mouse tail bleeding time and platelets activation.