Novel Immune Biomarker Distinguishes Respiratory Infections

A novel immune biomarker has been identified that discriminates between influenza and bacteria in patients with suspected respiratory infection.

Host response biomarkers can accurately distinguish between influenza and bacterial infection. However, published biomarkers require the measurement of many genes, thereby making it difficult to implement in clinical practice.

Investigators at the University of Sydney (Australia) sought to identify a single-gene biomarker with a high diagnostic accuracy equivalent to multi-gene biomarkers. Towards this end they combined an integrated genomic analysis of 1071 individuals with in vitro experiments using well-established infection models.

The investigators reported finding the single-gene biomarker, IFI27 (Interferon alpha-inducible protein 27), which had a high prediction accuracy (91%) equivalent to that obtained by multi-gene biomarkers. In vitro studies showed that IFI27 was upregulated by TLR7 (Toll-like receptor 7) in dendritic cells, antigen-presenting cells that responded to influenza virus rather than bacteria. In vivo studies confirmed that IFI27 was expressed in influenza patients but not in bacterial infection, as demonstrated in multiple patient cohorts.

In a large prospective study of patients presenting with undifferentiated respiratory illness (etiologies included viral, bacterial, and non-infectious conditions), IFI27 displayed 88% diagnostic accuracy and 90% specificity in discriminating between influenza and bacterial infections.

The biomarker IFI27 has been incorporated into the patented "High-risk Influenza Screen Test," which requires only a single drop of blood and a few hours to run on equipment already available in most pathology laboratories.

"By using the High-risk Influenza Screen Test we are eavesdropping on the immune system to pick up when the body first mounts a defense against a serious, life-threatening infection. The early warning means we have a greater chance to treat the patient's infection before it overwhelms them and potentially kills them," said first author Dr. Benjamin Tang, associate professor of intensive care medicine at the University of Sydney. "We can now test people during a pandemic, or outbreak of a new flu virus, to identify those who might be at greater risk of developing serious complications. The test works with any flu infection as it looks at how the body reacts rather than the strain or type of virus."

The study was published in the June 15, 2017, online edition of the journal European Respiratory Journal.

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