In a new study from NYU Grossman School of Medicine, researchers have discovered a mechanism that may explain why COVID-19 patients lose their sense of smell.
They found that infection with the pandemic virus, SARS-CoV-2, indirectly dials down the action of olfactory receptors (OR), proteins on the surfaces of nerve cells in the nose that detect the molecules associated with odors.
The study may also shed light on the effects of COVID-19 on other types of brain cells, and on other lingering neurological effects of COVID-19 like “brain fog,” headaches, and depression.
In the study, the team found that the presence of the virus near nerve cells (neurons) in olfactory tissue brought an inrushing of immune cells, microglia and T cells, that sense and counter infection.
Such cells release proteins called cytokines that changed the genetic activity of olfactory nerve cells, even though the virus cannot infect them.
Where immune cell activity would dissipate quickly in other scenarios, in the brain, according to the team’s theory, immune signaling persists in a way that reduces the activity of genes needed for the building of olfactory receptors.
The findings provide the first mechanistic explanation of smell loss in COVID-19 and how this may underlie long COVID-19 biology.
They also suggest how the pandemic virus, which infects less than 1 % of cells in the human body, can cause such severe damage in so many organs.
One unique symptom of COVID-19 infection is loss of smell without the stuffy nose seen with other infections like the common cold, researchers say.
In most cases, the smell loss lasts only a few weeks, but for more than 12% of COVID-19 patients, olfactory dysfunction persists in the form of the ongoing reduction in the ability to smell (hyposmia) or changes in how a person perceives the same smell (parosmia).
To gain insight into COVID-19-induced smell loss, the current authors explored the molecular consequences of SARS-CoV-2 infection in golden hamsters and in olfactory tissue taken from 23 human autopsies.
In the current study, the research team detected persistent and widespread downregulation of olfactory receptor building.
Other work posted by these authors suggests that olfactory neurons are wired into sensitive brain regions and that ongoing immune cell reactions in the nasal cavity could influence emotions, and the ability to think clearly (cognition), consistent with long COVID.
In the next step, the team is looking into whether treating hamsters with long COVID with steroids can restrain damaging immune reactions (inflammation) to protect nuclear architecture.
If you care about Covid, please read studies that Cannabis CBD may help protect against COVID-19, and CBD from cannabis may inhibit COVID-19 infection.
For more information about Covid, please see recent studies about wearable air sampler that could detect personal exposure to coronavirus, and results showing two paths toward ‘super immunity’ to COVID-19.
The study is published in Cell, and was conducted by Benjamin tenOever et al.
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