Identification of novel mechanistically distinct endotypes of pandemic influenza-associated acute respiratory failure

Respiratory viral pandemics result in large numbers of cases of acute respiratory failure arising from a single etiology, thus reducing the heterogeneity of precepting insult and allowing improved insight into the variation of host responses. In 2009-2011, an influenza pandemic occurred, with pH1N1 infecting millions of people worldwide. Here, we have used novel bioinformatic methods to combine clinical, protein biomarker, and genomic data from patients with influenza-associated acute respiratory failure to identify three mechanistically discrete sub-types with significantly different clinical outcomes. The three endotypes identified can be described as "neutrophil-driven" (16.3%), "adaptive" (51.9%), and "endothelial leak" (31.7%). The neutrophil driven patients display evidence of innate immune activation with associated multi-organ dysfunction and reduced 30-day survival. These patients could be differentiated from the adaptive endotype by an alteration in the GAIT-mechanism, a late transcriptional regulatory response to IFN-{gamma} that acts to suppress innate immunity by reducing caeruloplasmin mRNA translation. Patients with the neutrophil-driven endotype had significantly increased IFN-{gamma} levels but appeared unable to suppress their innate immune response. The endothelial leak endotype could be distinguished from both the neutrophil driven and adaptive endotypes by alterations in Slit-Robo signalling, a pathway important in the maintenance of endothelial barrier integrity; Although patients with this endotype required mechanical ventilation, they did not develop multi-organ failure in the manner of the neutrophil-driven endotype patients, and had significantly better clinical outcomes. Importantly, the endotypes identified were stable over 48 hours opening up the possibility of stratified interventional clinical trials in the future. One Sentence SummaryWe have identified three new mechanistically distinct subtypes of influenza associated acute respiratory failure, with differential clinical outcomes.