Investigating platelet-leukocyte-aggregate formation under shear stress conditions in vitro and in vivo

Introduction Platelets are primarily known for their function in hemostasis. However, they also play a role in the field of immunology. When inflammatory or thrombotic processes occur in the body, platelets can form aggregates (PLA) with leukocytes. A distinction can be made between platelet-neutrophil aggregates (PNA) and platelet-monocyte aggregates (PMA). The occurrence of PLAs has been frequently studied in inflammatory disease patterns and has already been considered as potential biomarkers for e.g. chronic obstructive pulmonary disease, consumptive coagulopathy, or sepsis.

Patients with a left ventricular assist device (LVAD) often suffer from infections due to immunosuppression and the exit site of the driveline. In addition, platelets are subjected to higher shear stress by the pump, which may lead to platelet activation and consequently to the formation of PLAs. Therefore, this study investigated the extent to which shear stress alone may contribute to the formation of PLAs.

Method D-Phenylalanyl-L-prolyl-L-arginine chloromethyl ketone (PPACK) anticoagulated blood was collected from healthy donors and patients with an LVAD. For part of the experiments a platelet inhibitor was added to the blood of the donors 15 min before shear stress exposure. Whole blood (from donors) was pumped at a defined shear rate through a PDMS-glass-based flow chamber (height 100 µm, width 1000 µm, length 5 cm, with or without a 75% stenosis), applying a defined shear stress to the cells. After shear stress exposure, PLA, PNA and PMA were determined by flow cytometry.

The study received a positive vote from the ethics committee (AZ: 2022-1015).

Results The formation of cell aggregates in the flow chamber model without stenosis showed a significant increase exclusively for the formation of PMAs. When 75% stenosis was present in the model, increased levels of PLA, PNA, and PMA were measured. The values were increased at both the lower and higher shear rates relative to the control. However, no significant difference was observed between the lower and higher shear rates.

Increased levels of PLAs could be measured in the patient samples compared to control samples.

Conclusion It could be shown here that an increased shear rate can contribute to the formation of PLAs in general. Thereby, not the absolute level of the shear rate but an acceleration in the flow system seems to be decisive. Increased levels of PLAs were also measured in the patients with implanted LVAD. Because PLAs also have a prothrombotic effect, the detection of PLAs in this patient population could be a marker for an increased risk of thrombosis. Whether there is an association between elevated PLAs and thromboembolic events in these patients needs to be explored in further studies.

Conflict of Interest

Ingvild Birschmann received speaker’s honoraria from Bristol-Myers Squibb/Pfizer, CSL Behring, LFB biomedicaments, Octapharma AG and Siemens Healthcare and performed contract research for Siemens Healthcare. Ingvild Birschmann is supported by means of medical writing from CSL Behring and is a member of the advisory board/expert testimony of LFB biomedicaments, Portola Pharmaceuticals, Siemens Healthcare and CSL Behring. All other authors have no competing interests.

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Artikel online veröffentlicht:
26. Februar 2024