Human anti-heparin-platelet factor 4 antibodies are capable of activating primate platelets: Towards the development of a HIT model in primates

In the first step to establish an animal model of heparin-induced thrombocy topenia (HIT) that is physiologically relevant to humans, studies were unde rtaken to determine the similarities or differences between human and non-h uman primate (Macaca mulatta) platelets in HIT assay systems. The collagen- , ADP-, and TRAP-induced platelet aggregation, and flow cytometric analysis of P-selectin expression and microparticle formation were similar for both species platelets (p>0.1, n=18 each). The classical HIT assays using plate let-rich plasma (PRP) as well as a flow cytometric assay revealed the activ ation/aggregation and serotonin release assay (SRA) profiles for both prima te and human platelets were similar in response to human HIT positive sera (r(2)=0.81). All assays were heparin concentration-dependent; heparin, at 0 .1 U/mL, produced maximum and similar platelet activation/aggregation and S RA responses with both primate (76+/-7%, n=18) and human (68+/- 11%, n=20; p>0.1) platelets. At concentrations greater than or equal to 10 U/mL, hepar in suppressed the platelet aggregation and SRA responses in both systems. P rimate and human platelets displayed similar behavior to low molecular weig ht heparin and pentasaccahride in HIT assay systems, Immunoglobulins isolat ed from serum of patients with HIT (n=6) caused activation/aggregation of h uman (65+/-18%, n=10 donors) and primate (79+/-12%, n=6 monkeys, p>0.08) pl atelets. Unlike human platelets, the primate platelets exhibited a more con sistent aggregation/release response (15 out of 18 primate platelets reacti ve). In contrast, human donors showed wide variations in the activation/rel ease response (4 out of 10 reactive). These observations suggest that prima te platelets are activatable by anti-H-PF4 antibodies, and support the hypo thesis that primates can be used to develop an animal model to study the pa thogenesis of HIT. (C) 2000 Elsevier Science Ltd. All rights reserved.