(422) Investigating the antibacterial and pro-coagulant activity of neutrophil-derived extracellular vesicles induced by phagocytosis of S. aureus.

Introduction/Rationale: Extracellular vesicles (EVs) are small nanosized particles with the ability to influence host-pathogen interactions. Their function depends on several factors, including the status of the EV-releasing cell type. For example, EVs produced from neutrophils (PMN) challenged with S. aureus (PMN-SA-EVs) initiate the intrinsic pathway of coagulation, but EVs released spontaneously from neutrophils do not. The goal of our work was identifying the mechanism for the pro-coagulant activity and identify other effects PMN-SA-EVs have on the host response.

Methods: To test whether an EV surface protein was required for pro-coagulant activity, we treated PMN-SA-EVs with proteinase K (PK) and measured thrombin generation (TG). We also explored whether PMN-SA-EVs had antibacterial properties. Toward this goal, we investigated the effect of EVs on transcription in monocyte-derived macrophages and on the growth of bacteria. Macrophages were treated with spontaneously released PMN-EVs or PMN-SA-EVs.

Results: In support of protein involvement, PK treatment of PMN-SA-EVs reduced TG.There were minimal transcriptional differences between the two conditions, with transcriptional responses corresponding to donor identity instead of treatment groups. In contrast, EVs had a direct effect on bacteria with PMN-SA-EVs reducing growth of new S. aureus cultures.

Conclusion: This work better elucidates the role of PMN-SA-EVs in host-pathogen interactions, and our future efforts aim to uncover the mechanisms in more detail.