When cells in the nose sense potential invaders they release tiny sacs that fight them off and prime other cells to resist an onslaught.
Dr Benjamin Bleier, a sinus surgeon at Massachusetts Eye and Ear Hospital said, “we have demonstrated in a live patient that the immune system attacks pathogens before they get into the body, it is the only example of this that we know of. The nose is a crucial frontier: every breath we take may contain dangerous bacteria, so the cells lining the nasal cavity secrete mucus that traps tiny particles.
Hairs on the surface of these cells, called cilia, beat to move the mucus along. Instead of being swept forwards so it can be rapidly expelled, the mucus is swept back towards the throat. You swallow it and then the gut deals with it from there.”
Bleier’s team and other researchers have recently found that, as well as secreting mucus the cells in the nasal cavity release billions of tiny sacs called exosomes. Once in the mucus, these sacs fuse with other cells, delivering proteins or RNA.
Suspecting that exosomes are part of a previously unknown defence system, Bleier and his colleagues studied tissue in the lab and people undergoing nasal surgery and now have strong evidence of this theory.
They found that when cells at the front of the nose are exposed to a potentially dangerous bacterium, the number of exosomes released into the mucus doubles within 5 minutes.
Their experiments suggest that exosomes can kill pathogens directly, although they don’t yet know how.
“They are as powerful at killing bacteria as an antibiotic, says Bleier, but not all exosomes kill. Many do not attack bacteria but instead fuse with cells towards the back of the nose and seem to both alert these cells and arm them with antibacterial proteins, which may explain why mucus is swept backwards. Mucociliary clearance is not just a garbage dump, it’s actually a circulatory system”.
The team now hopes to identify how exosomes fuse with cells, which would allow them to develop artificial exosomes that deliver drugs more effectively.
Dr Cecilia Lasser, at the University of Gothenburg in Sweden, whose team has also been examining whether exosomes have a role in the immune system, agrees.
Exosomes were discovered in 1983, but it is only in the last decade that interest in them has increased. As well as seeming to arm our noses against invaders, they are involved in all kinds of processes, from normal body functioning to diseases, including cancer and asthma.
Michael Le Page
Updated February 8th 2019
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