The route of the new coronavirus in and out of the nasal cavity is determined

In a study published in the journal Cell, Dr.
Peter Jackson, a professor of pathology, microbiology and immunology at Stanford University, the team pinpointed the pathways
by which the new coronavirus enters and leaves nasal cells.
Researchers say the upper respiratory tract is not only a source of lung infections, but also a source of transmission to others
.
Suppressing the entry and exit of the virus in respiratory cells has been shown to be effective
in reducing the spread of highly contagious new coronavirus.

The epithelial tissue of the nasal cavity and respiratory tract is mainly composed of 3 cell types: basal cells, goblet cells, and polycilia cells, which account for about 80%
of the total number of nasal epithelial cells.
Polycilia cells form a protective barrier that prevents the virus from entering the respiratory tract
.
The researchers magnified two structures found on multiciliated epithelial cells: cilia and microvilli
.

The researchers used a sophisticated tissue culture method to generate respiratory epithelial organoids to mimic the normal respiratory tract
.
Although lacking blood vessels and immune cells, these organs otherwise fully cover the structure of the nasal mucosal epithelium, including an intact mucus layer and well-developed polycilia cells
.

The researchers placed the cultured organoids in
the same Petri dish as the new coronavirus.
Electron microscopy showed that the virus initially attached only to
cilia.
After the organoids were incubated with the novel coronavirus for 6 hours, many viral particles spread from the tip down on both sides
of the cilia.
Even after 24 hours, the virus replicates
in only a few cells.
Large-scale replication takes 48 hours
.

Studies have found that reducing the level of a protein in nasal epithelial cells, which is essential for cilia formation, can greatly slow down infection with the new coronavirus, proving that human cilia nasal epithelial cells are the main entry site
of the new coronavirus in nasal epithelial tissue.

The researchers pinpointed enzymes in the cells that were activated in large numbers after infection with the new coronavirus, causing the microvilli to turn into huge, branched tree-like structures on which viral particles
were attached.
These viruses can be pushed into the mucin-mucin layer, where they can "float" along the mucus and infect other cells farther away
.
Inhibiting these enzymes stops this mutation and greatly reduces the spread
of the virus to other cells.

These findings identify new targets for nasal drug development that blocks cilia movement or microvilli enlargement to prevent even unknown respiratory viral infections
.