Infection in patients with systemic inflammation is difficult to diagnose with a single biomarker. We aimed to clarify the time course of change in the gene expression profile of innate immune receptors in infectious or sterile inflammation and to establish an early diagnostic method using canonical discriminant analysis (CDA) of the gene expression profile.METHODS
To compare infectious and sterile inflammation, we used cecal ligation and puncture (CLP) and 20% full-thickness burn injury (Burn) models. C57BL/6 mice underwent sham treatment (n = 9 × three groups), CLP (n = 12 × three groups), or Burn (n = 12 × three groups) injury. Mice were killed at 6, 12, and 24 hours after injury, and total RNA was extracted from whole blood. We used quantitative real-time polymerase chain reaction to investigate gene expression of innate immune receptors Toll-like receptor 2 (TLR2), TLR4, TLR9, NLRP3 (nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3), and retinoic acid–inducible gene I. To evaluate all gene expression together as patterns, each value was standardized, and CDA was performed at each time point.RESULTS
Gene expression of TLR2 and TLR4 was already significantly increased in both CLP and Burn compared with sham mice at 6 hours after injury (p < 0.05). Gene expression of TLR9 was significantly decreased in CLP compared with sham and Burn mice at 12 hours and 24 hours after injury (p < 0.05) but not at 6 hours. Gene expression of NLRP3 was significantly increased in CLP and Burn compared with sham mice at 6 hours and 24 hours after injury (p < 0.05). In the CDA, each group showed distinctive gene expression patterns at only 6 hours after injury. Each group was clearly classified, and the classification error rates were 0% at all of the time points.CONCLUSIONS
Canonical discriminant analysis of the gene expression profile of innate immune receptors could be a novel approach for diagnosing the pathophysiology of complicated systemic inflammation from the early stage of injury.