New research on how our immune system works shows how the body mobilizes a previously unknown defense against viruses and bacteria- and thus why we do not constantly get ill despite the viruses around us. 

Fever, sore muscles and other influenza-like symptoms are typical signs that your immune system is fighting against viruses and bacteria. The unpleasant condition is, among other things, due to the body forming a substance called interferon, which must defeat the virus. For many years researchers and doctors have assumed that this was the body's earliest response when attacked by various infections.

But new research shows that the body's very first defense mechanism is not interferon, but rather a hitherto unknown mechanism, which begins working even earlier. 

The newly discovered immune reaction is activated when the body's mucous membranes are disrupted, as they are when viruses and bacteria attempt to establish an infection. The immune system recognizes the virus and produces a substance that neutralizes the uninvited guest. The process goes on continuously without us being aware of it. If this first immune reaction is not sufficient to suppress the virus, the infection establishes itself in the body. This in turn triggers the next reaction involving interferon, which not only helps to fight the virus, but also means we become ill.  

Experiments on mice have shown that mice, lacking this first defence mechanism, become ill if they are exposed to herpes virus, while normal mice remain healthy.

"We do not yet know the precise significance of this mechanism, but it may explain why some people become more ill from viral infections such as influenza than others. The same may apply to other viral infections that are initiated on mucous membranes such as HIV and herpes. We will now begin to map out the molecules that are involved. Once we have done this, it will be possible to identify people with defects in the mechanism, just as there is a potential to develop new forms of treatment. At the same time, the mechanism may turn out to have significance also for non-viral diseases, so continued research into this area shows great potential," says Soren Riis Paludan of Aarhus University.

 Published in Nature Immunology.