Loss of smell due to COVID-19 linked to destruction of nasal cells

The ongoing loss of smell in COVID-19 may be caused by cell destruction in the nose. A new immune response study sheds light on whether the coronavirus damages the nose or the brain.

Millions of people who have lost their sense of smell after contracting Covid may have a permanent abnormal immune response that destroys cells in the nose, researchers say.

According to The Guardian, doctors analyzed tissue from the noses of COVID patients and found that those people who had long-term problems with smell had inflammation-causing immune cells inside the thin nasal mucosa that potentially destroyed vital sensory nerve cells.

Dr. Bradley Goldstein, an associate professor of neuroscience at Duke University in North Carolina, said nasal mucosal tissue “contained unique immune cells that produce inflammatory signals, combined with fewer olfactory nerve cells.” An unusual immune response was observed only in patients in whom the loss of smell persisted for several months.

“It seems that there is an unresolved local immune response that thin olfactory cells see,” the scientist added.

Ever since doctors noticed that many COVID patients have lost their sense of smell, it has been unclear whether the virus is damaging sensory cells in the nose, areas of the brain that process olfactory information, or both.

Researchers studied tissue biopsies from the nasal mucosa of 24 COVID patients, including nine people who lost their sense of smell for at least four months. Tissue from the latter group showed that T cells involved in inflammation had infiltrated the nasal mucosa, where olfactory nerve cells were found. An unusual immune response was observed despite the fact that the patients had no detectable COVID virus, suggesting that it persisted after the infection was cleared.

When the researchers looked at the number of sensory nerve cells involved in smelling, they found that those who suffered long-term loss of smell had noticeably fewer of them, possibly because the delicate tissue of the nasal mucosa had been damaged by T cells. inflammation. Such wayward immune responses could explain other long-term symptoms of COVID, Dr. Goldstein said.

As researchers reported in the BMJ this year, at least 5% of people who lose their sense of smell during a COVID infection do not regain their sense of smell quickly or completely, which is about 15 million people worldwide. “We don’t have specific effective treatments at this time,” Goldstein said. — To develop treatments, we need to understand the pathobiology of the problem: what is damaged and where.”

In their paper in the journal Science Translational Medicine, the researchers explain how the findings could pave the way for new treatments for smell loss after COVID-19. One option is to block inflammation-causing immune cells locally in the nasal mucosa, a part of the body that is easily accessible with creams and sprays. “We are encouraged by these findings and hope that new treatments may emerge,” said Dr. Goldstein.

Danny Altmann, professor of immunology at Imperial College London, called the researchers’ work “an important addition to deciphering many of the pathological tricks of Sars-CoV-2.”

“As we saw earlier, profound symptomatic changes can occur in the absence of a live virus found at the scene,” he said. — Loss of smell has become one of the key mysteries, and these findings offer an answer, along with previous data on changes in the olfactory bulb in the nervous system.”

“In patients with COVID-19, persistent problems with smell have been shown to be associated with shrinking areas of the brain associated with our sense of smell,” comments neuroscientist Dr Gwenael Duo, who studied the effects of covid on the brain at the University of Oxford. — Inflammatory processes are known to continue in the brain after Sars-Cov-2 infection, whether or not the virus itself is present, and this biopsy study now provides additional evidence that this specific brain loss may be due to persistent inflammation and loss of olfactory neurons. in the nasal cavity itself.