Thrombin Generation Responses to Human Factor XIa in Plasma of Animal Species

Abstract 5142

Thromboembolic events (TEE), including deep venous thrombosis and myocardial infarction, have been reported in patients receiving immunoglobulin intravenous (IVIG). Recent research showed that many TEE-induced IVIG samples were contaminated with human coagulation factor XIa (FXIa). At present, there is no systematic investigation of animal models that can be used to assess FXIa dependent thrombogenicity risk in animals and be predictive for human response. To assist in species selection for in vivo animal studies, we compared the magnitude and kinetic parameters of thrombin generation in commercially available human and animal plasma samples in response to human FXIa. A low sample volume, highly reproducible thrombin generation test was developed for this study. In our assay, thrombin generation in plasma (20 microliters) is initiated by physiological activator tissue factor in the presence of procoagulant phospholipids, sample (FXIa), buffer and calcium (combined volume of all additions to plasma is 20 microliters). The thrombin generation response to human FXIa was evident from increased thrombin peak height and/or shortened time to thrombin peak. The minimal effective FXIa concentration was species-dependent and ranged from below 0. 1 pM in monkey plasma to over 100 nM in BalbC mouse. The FXIa sensitivity of commercial plasma samples was aligned in the following order: Rhesus and Cynomolgus Monkeys > Human Donors > New Zealand White Rabbit and Sprague Dawley Rat > Hartley Guinea Pig and CD1 Mouse > Lewis Rat > Wistar and Fisher 344 Rats > C57BL6 and Blab C Mice. However, further experiments on freshly collected guinea pig plasma demonstrated that preanalytical variables, notably, blood collection and plasma freezing and thawing techniques, are critical to achieve optimal sensitivity of the thrombin generation test to FXIa. Therefore, variable quality of commercial plasma may have affected observed interspecies differences in thrombin generation. Collectively, these findings will help to clarify differences in minimal thrombogenic doses of FXIa observed in various animal models and levels of FXIa associated with thrombotic events in humans.

This research was supported by the FDA Office of Women's Health grant (2012).