Innate correlates of influenza clinical outcomes in a multicenter, longitudinal study of critically ill children

Paradoxically, influenza infection can trigger pro- and anti-inflammatory responses, both of which can lead to significant morbidity and mortality. Inflammation can lead to septic shock and acute lung injury (ALI), while suppression can slow viral clearance and increase susceptibility to bacterial coinfection (BCo). We collected and analyzed lung and peripheral blood samples from a multi-center cohort of critically ill children with influenza infection (N = 171) to better understand innate signatures of disease. Samples were collected at admission to the PICU and assayed for levels of 42 cytokines and chemokines. We found intra-compartment analyte correlations were high, while those between compartments were comparatively weak. To increase statistical power and identify groups of co-signaling cytokines, we pre-specified an unsupervised hierarchical clustering analysis to form influenza-specific modules. Some modules were consistent with the literature; e.g. IL4, IL5, IL9 and IL13 (Th2-like) clustered within both compartments. We hypothesized that modules would associate with shock, ALI and death or near death (ECMO). A pro-inflammatory PB module including IL6, IL8, IL10, IP10, GCSF and MCP1 was associated with shock (FWER plt;1e-4; OR 3.4) and ALI (FWER p=0.003; OR 2.2), validating previous studies. Inverse associations were also identified with lung and serum modules, only after adjusting for patients’ mean analyte levels, suggesting that relative levels are important. An integrative analysis of lung and PB analytes showed that BCo has a distinct signature from shock that can be used as a biomarker to distinguish the two. Significant modules also generated hypotheses about analytes that could be targeted by novel therapies.