(It’s well known that COVID-19 can affect your sense of smell, but in some cases, that sense of smell doesn’t return properly. Now, new research explains why.
SARS-CoV-2 infection causes the immune system to continuously attack nerve cells in the nose, the new study finds, and then there is a drop in the number of those nerve cells, preventing people from sniffing and feel like they usually would. .
In addition to answering a question that has baffled experts, the research could also help us understand the long COVID and why some people cannot fully recover from COVID-19.
“Fortunately, many people who have an impaired sense of smell during the acute phase of viral infection will regain their sense of smell within one to two weeks, but some don’t,” says Duke University neurobiologist Bradley Goldstein in North Carolina.
“We need to better understand why this subset of people will continue to have persistent smell loss for months or even years after being infected with SARS-CoV-2.”
The team studied samples of nasal tissue – olfactory epithelium – taken from 24 people, including nine with long-term loss of smell after having COVID-19. This tissue contains the neurons responsible for detecting odors.
After a detailed analysis, the researchers observed the widespread presence of T cells, a type of white blood cell that helps the body fight infections. These T cells caused an inflammatory response in the nose.
However, as with many other biological responses, T cells apparently do more harm than good and damage olfactory epithelial tissue. The inflammatory process was still evident even in tissues where SARS-CoV-2 was not detected.
“The results are striking,” says Goldstein. “It almost looks like some sort of autoimmune-like process in the nose.”
While the number of olfactory sensory neurons was lower in study participants who had lost their sense of smell, the researchers report that some neurons appear able to repair themselves even after T cell bombardment – an encouraging sign.
The researchers suggest that similar inflammatory biological mechanisms may be behind the other symptoms of long COVID, including excessive fatigue, shortness of breath, and “brain fog” that makes it difficult to concentrate.
Next, the team wants to examine in more detail which particular tissue areas are damaged and which cell types are involved. This, in turn, will pave the way for the development of possible treatments for those who suffer from long-term loss of smell.
“We hope that modulating the abnormal immune response or repair processes in the noses of these patients might help to at least partially restore the sense of smell,” says Goldstein.
The research has been published in Science Translational Medicine.
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