Neutrophil Extracellular Traps (NETs) in Thermal and Traumatic injuries

Abstract

Severe thermal injuries and trauma result in considerable immunological and haemostatic disturbances, increasing the risk of sepsis, disseminated intravascular coagulation (DIC) and multiple organ failure (MOF). The formation of neutrophil extracellular traps (NETs), an essential innate response to infection and tissue damage, leads to elevated circulating levels of NET-derived chromatin and cell-free DNA (cfDNA), which act in defence but also as a trigger for immunothrombosis. Our research indicates that post-burn and trauma cfDNA primarily consists of nucleosome fragments (~150 bp), with higher molecular weight nucleosome oligomers (i.e., ~ 300 and 450 bp) in ultra-early samples (< 1 hour) obtained from trauma patients. However, absence or low nucleosome levels in the majority of admission samples in burns were confirmed along with the presence of increased levels of large undegraded NET-derived chromatin captured using microfluidic chips. CfDNA levels also correlate with neutrophil activation and the extended neutrophil parameter Y (NEUT-Y). The breakdown of NETs into circulating cfDNA in the form of nucleosomes, increased NEUT-Y levels with production of Immature Granulocytes (IG) are potential early biomarkers for predicting sepsis in burns. Moreover, high levels of IL-8 are released and are major mediators of NET formation in burns. Haematological studies demonstrated classical post-injury nadir and recovery patterns in platelet counts following thermal injury. Severe burns also led to high significant impairment of high shear platelet function in the early days after the injury (e.g. day 3) and were associated with reduced ex vivo thrombus formation. Additionally, post-injury high levels of VWF and low levels of ADAMTS13 although not correlated with platelet function correlated with NET biomarkers, NEUT-Y and cfDNA, providing a further important contribution to NETosis. This thesis illustrates the importance of the mechanisms and dynamics of NET production and breakdown as biomarkers, therapeutic targets and in the pathogenesis of post-injury sepsis, DIC, and MOF.