New research may explain why some never get the flu

By Stephen Beech

A protein found in sweat, saliva and tears may explain why some people never get the flu, according to a new study.

Dermcidin has antiviral activity against the virus and may shape susceptibility to potentially deadly influenza, say scientists.

The influenza virus is a leading cause of respiratory infections and a recurring public health issue worldwide.

But up to 35% of people exposed to the flu virus never develop symptoms.

However, the underlying mechanism is not understood.

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Spanish scientists tested the potential role of the differences in responses between people in the performance of their immune systems, focusing on antimicrobial peptides — also known as AMPs.

Dr. Alex Mira and Dr. María Ferrer, of the University of Valencia, and their colleagues searched for AMPs with antiviral activity by analyzing mouthwash samples from 19 healthcare workers who never suffered from flu-like symptoms.

"The analysis suggested that the AMP dermcidin, which is found in saliva, sweat and tears, could be responsible for resistance to influenza symptoms," Mira said.

"In vitro experiments showed that dermcidin exerted antiviral activity against the two main subtypes of circulating human influenza virus by binding to the viral protein hemagglutinin and blocking viral entry into host cells."

Experiments in mice showed that dermcidin protects against influenza A disease, according to the findings published in the journal Proceedings of the National Academy of Sciences (PNAS).

"In addition, dermcidin levels were approximately sixfold higher in the uppermost part of the throat in 30 asymptomatic individuals, compared with 29 susceptible peers, indicating a protective role against flu symptoms," Ferrer said.

Ferrer added: "The study suggests that dermcidin could serve as a potential biomarker of severe susceptibility to influenza infection."