Scientists
have found that two types of cells found in the nose are a mechanism that the SARS-CoV-2
virus uses as a means to enter the body and trigger an infection. Significantly,
nasal swabs have yielded higher viral loads than throat swabs.
The
research, from the Netherlands, shows that once inside the human body, human
enzymes termed proteases (specifically, in relation to the novel coronavirus,
this is a protease called TMPRSS2 or ‘transmembrane protease, serine 2’) are
capable to cleaving the coronavirus in half.
With
this process, one viral fragment
functions
to bind to a receptor termed ACE2, and this is a path to get into cells. The coronavirus deploys its spike
glycoprotein (the ‘corona’ shape), to bind its receptor, and mediate membrane
fusion and virus entry.
Proteases
Proteases are
enzymes
that catalyze the breakdown of proteins into smaller polypeptides or single
amino acids. This happens by cleaving peptide bonds found within proteins through
triggering a reaction called hydrolysis.
This
is an area of focus because ACE2 and
TMPRSS2 have been detected in both nasal and bronchial epithelium by immunohistochemistry.
Key
risks around the nose
A
science team from University Medical Center Groningen, looking at different
points of viral entry and the relative risks around this, indicate that with
the nose,
cells called goblet and ciliated cells contain particularly high levels of the protease
TMPRSS2 as well as ACE2 proteins.
This
important finding could provide the answer as to why the virus can be
transmitted so readily.
To arrive
at the conclusion about the vulnerability around the nose, the research team
drew upon datasets located within the Human Cell Atlas (HCA) to identify the
cells that express ACE2 and TMPRSS2.
This
inquiry also signalled that cells in the lining of the intestine and the cornea
of the eye also provide easy pathways for the virus to cause an infection.
Research
significance
Talking
to the science website Laboratory Roots, the lead researcher Dr. Martijn Nawijn
states:
“This is the first time these particular cells in the nose have been associated
with COVID-19…our findings are consistent with the rapid infection rates of the
virus seen so far.”
He
adds: “The location of these cells on the surface of the inside of the nose
make them highly accessible to the virus, and also may assist with transmission
to other people.”
Such
knowledge can provides the basis for developing potential treatments to reduce
the spread of the virus.
Research
paper
The research
has been published in the journal
Nature Medicine. The research paper is titled “SARS-CoV-2 entry factors are
highly expressed in nasal epithelial cells together with innate immune genes.”
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