Immune cells in the nose remember past viruses, and attack them accordingly, shows a new study published in Science Immunology.
The nose of mice remembers: specific immune cells in their nasal tissues were found with the ability to remember, and thus swiftly attack, influenza viruses that had previously infected them.
The immune system has a wide array of combat techniques to protect the body against pathogens. One of its many tricks is to have cells dedicated to remembering an attack so that it is better able to get rid of the foreign bodies if they enter the body another time. However, what was unknown until now was that the nose was also equipped with this type of memory immune cell. The presence of tissue resident memory T cells in the nose has been shown for the first time, thanks to the new study.
Memory T cells are known to become residents in certain tissues, like those of the brain, skin, intestines, liver, and lungs. They operate by patrolling around (sometimes, for years on end) after a localised infection. These cells are “basically sitting there waiting in case you get infected with that pathogen again”, explains study author Linda Wakim. If the pathogen does appear again, the T cells can effectively and quickly kill infected cells; they also release chemical signals (cytokines) to trigger an influx of other immune cells to gang on the enemy. The ones present in the lungs, however, behave slightly differently from the majority: they have relatively shorter-term memories. Wakin and his colleagues, therefore, wanted to find out whether tissues of other parts of the respiratory system (like the nose) also had this type of memory or not.
The team sprayed flu virus in the noses of mice, and observed the ensuing response. They found that, following the infection, the nose called for immune cells with long-term memories. These nasal resident memory T cells settled into the nasal tissue, lying in wait for the virus in case the latter paid a visit again. These memory cells stayed in the animals’ nose for a minimum of a year, representing a third of the life of mice, thus demonstrating that they have long-term memories, unlike the lungs. The difference between the latter and the nose has, however, not been deciphered. Perhaps, the lungs do not need the longer-term memory because the nose is already catering for security measures? The new findings show that memory T cells in the upper respiratory system might be preventing viruses from reaching the lungs. Wakin still believes that investigating this aspect will possibly allow researchers to enhance the T cell memory of lungs.
Also, since the T cells might be working for the prevention of flu, it is hoped that nasal spray vaccines meant to boost their number might become a thing in the future.
It is not yet confirmed whether the human nose also has resident memory T cells though. But, the researchers are positive that this might be the case.