# Platelet‐Activating Factor Promotes Neutrophil Activation and Platelet–Neutrophil Complex Formation

## TL;DR

This study shows how platelet-activating factor (PAF) activates neutrophils and forms platelet-neutrophil complexes, which could lead to new treatments for inflammation-related diseases like sepsis.

## Contribution

The study reveals novel mechanisms of PAF-induced neutrophil activation and platelet-neutrophil complex formation using an animal-free ex vivo model.

## Key findings

- PAF rapidly changes neutrophil phenotype by upregulating CD10, CD11b, and CD66b and downregulating CD62L.
- Platelet–neutrophil complexes (PNCs) enhance reactive oxygen species formation and phagocytosis compared to neutrophils alone.
- Iloprost and anti-CD62P may modulate PAF-induced platelet–neutrophil interactions and neutrophil functions.

## Abstract

Controlling excessive inflammation remains an unmet clinical need, for example, during sepsis or after severe injuries. Platelet‐activating factor (PAF) is central in thromboinflammatory processes. However, its role in the interaction of platelets and neutrophils requires further insights. Therefore, we elucidated PAF‐related neutrophil activation, including platelet–neutrophil complex (PNC) formation and investigated potential strategies to modulate PAF‐related inflammation. For the translation of the PAF‐mediated inflammation, we applied an animal‐free human ex vivo whole blood model. The neutrophil phenotype, its function, and PNC formation were studied by flow cytometry and platelet‐related activity was assessed by light microscopy and aggregometry. PAF induced a rapid and dose‐dependent change in neutrophil phenotype, as evidenced by CD10, CD11b, and CD66b upregulation and CD62L downregulation. Moreover, PAF increased the generation of reactive oxygen species (ROS), phagocytic activity and PNC formation. Interestingly, PNCs displayed significantly enhanced ROS formation and phagocytosis compared to neutrophils without attached platelets, whereas these differences were not observed regarding phenotype changes. Furthermore, the findings were confirmed in a clinically relevant ex vivo whole blood model of lipopolysaccharide‐ or PAF‐driven inflammation. In summary, the present study elucidates PAF‐driven effects on neutrophils and their interaction with platelets. The findings might help in developing therapeutic approaches to modulate PAF‐related thromboinflammation, for example, during sepsis.

The present study analysed the effect of the proinflammatory mediator platelet‐activating factor (PAF) on neutrophils both in vitro and in an animal‐free ex vivo whole blood model, with a particular focus on the formation of platelet–neutrophil complexes (PNCs). PAF triggered neutrophil activation (arrows), which was partially aggravated (+) or unchanged (−) by the formation of PNCs. Furthermore, potential pharmacological agents (e.g., iloprost, anti‐CD62P) and their effects on PAF‐induced platelet–neutrophil interactions and on neutrophil phenotype and effector functions were studied.