Covid-19 - This is why smokers are particularly at risk

Smoking inhibits the formation and maturation of airway stem cells. This greatly increases the risk of a severe course of Covid-19.

Los Angeles (U.S.A.). At the beginning of the Covid-19 pandemic studies already provided the first indications that smoking significantly increases the risk of a serious

disease course. According to science the likely reason for this is that the substances contained in cigarette smoke increase the number of ACE2 receptors in the lungs. These are used by SARS-CoV-2 as docking points. However this thesis has not yet been confirmed.

Scientists from the University of California in Los Angeles (UCLA) have now used so-called air-liquid interface cultures to investigate why smoking increases the risk of a severe course of Covid-19. With the cell culture method used for this purpose the human mucous membrane cells have direct contact with the air just like in the respiratory organs.

Replica of the upper respiratory tract

According to the study published in the journal Cell Stem Cell the model simulates the upper airways i.e. the first place that SARS-CoV-2 attacks in humans. As Brigitte Gomperts explains This is the area that the mucus produces to trap viruses, bacteria and toxins, and that contains cells with finger-like cilia that then carry the mucus away. To tudy the effects of cigarette smoke part of the Cultures steamed once a day for a short period of time. After four days the cell cultures were infected with SARS-CoV-2.

Smoke exposure promotes the spread of the virus

The later investigation shows that the smoke exposure of the cell cultures greatly increased the multiplication of the coronavirus compared to the control group. According to study director Arunima Purkayastha the viral load in the cultures that had previously been exposed to tobacco smoke was two to three times higher than in the controls. In addition significantly more mucous membrane cells were infected with viruses in the cell cultures with smoke exposure and the number of cellular suicide cells was also dead significantly higher.

Purkayastha states that this demonstrates that even a relatively short-term exposure of the airways to tobacco smoke worsens the infection because all cells originally came from healthy non-smokers.

Inhibited immune response of airway cells

The scientists cite a possible reason for the significantly higher susceptibility that cigarette smoke inhibits the formation and maturation of respiratory stem cells. These are crucial for the repair of the mucous membrane. Gomperts explains that if you imagine the airways as the walls of a castle, smoking breaks holes in these protective walls.Compared to non-smokers Covid-19 therefore kills more mucous membrane cells in smokers that cannot be completely replaced.

Tobacco smoke also triggers an immune response in the airway cells. According to experiments this is due to the fact that the smoke reduces the production of the immune messenger substance interferon. According to Purkayastha smoke exposure prevents an effective interferon-based immune response of the cells to SARS-CoV-2 and leads to a more active infection.Smoking weakens the natural defense mechanisms and thus makes it easier for the virus to attack the cells.

Further studies are now to investigate whether passive smokers also have a higher susceptibility and whether the number of daily cigarettes influences the susceptibility of smokers. It is also being investigated whether the susceptibility is also increased in former smokers.