People with asthma would be protected from severe forms of Covid-19. This paradox was explained by scientists in a recent publication in the journal PNAS. Indeed, it would seem that asthmatics present a double barrier against infection by SARS-CoV-2. It would be combined by the overproduction of mucus and protection by anti-inflammatory molecules overrepresented in asthmatics. On this World Asthma Day, Health on the Net explains these results.
Asthma and Covid-19, false friends?
Covid-19, a respiratory attack
For more than 2 years, the pandemic Covid-19 has prompted doctors and scientists to dissect this pathology, from its mechanisms to its symptoms. Although it takes various forms, we currently know that Covid-19 generally manifests itself by:
- Fever ;
- Muscle pain such as aches ;
- Headaches ;
- Fatigue;
- Respiratory system damage that may lead to respiratory distress.
Asthma, a chronic respiratory disease
This world dayasthma is an opportunity to make the general public aware of this pathology which affects more than 4 million people in France. Asthma is a chronic respiratory condition caused by permanent inflammation of the bronchial tubes. It is manifested by episodes of difficulty breathing (dyspnea).
Asthma is multifactorial. Indeed, in the case of allergic asthma, it is triggered in the presence of an allergen such as pollen or mould. The presence of the allergen causes a cascade of chemical phenomena. Thus, it will activate the production of cytokines and mucus in the lungs of patients.
To know ! The cytokines are chemical messengers of different natures. In the case of allergic asthma, it is interleukins 13 (IL-13), anti-inflammatory cytokines, which are overexpressed. They induce an overproduction of mucus by lung cells.
On paper, everything suggested that people with asthma would be patients at risk of a severe form of Covid-19. But, it is nothing. Epidemiological studies have not shown an association between being asthmatic and a greater risk of a severe form of Covid-19. Apart from patients with severe asthma (5% of the asthmatic population). On the contrary, researchers have shown that people with asthma, especiallyallergic asthmawould be protected against SARS-CoV-2 infection.
Asthma against Covid-19: a physical barrier formed by mucus
In a recently published study, the researchers wanted to explain the paradox of a potential protection against severe forms of Covid-19 by asthma. For this, they imitated allergic asthma on lung cells, by putting them in the presence of IL-13. They then infected them with SARS-CoV-2.
The results of the study highlight that allergic asthma confers two types of protection against Covid-19. Indeed, the production excessive de mucus by asthmatic lung cells provides a physical barrier limiting SARS-CoV-2 infection. Cells not treated with IL-13 also produced mucus during SARS-CoV-2 infection, but were quickly overwhelmed by virus multiplication.
A chemical barrier thanks to anti-inflammatory cytokines
To go further, the researchers then treated the lung cells with IL-13 but blocking the production of mucus. They observed that the treated cells had a lower viral load than those not treated with IL-13. This can be explained in two ways.
On the one hand, IL-13 decreases the production of receptors allowing the entry of SARS-CoV-2 into lung cells. Thereby, the virus has a much more difficult access to the cells. On the other hand, without IL-13, infected cells produce SARS-CoV-2 virions that facilitate the contamination of neighboring cells. Thus, the mechanisms elucidated in this study show a significant decrease in virus entry in the lung cells, from its replication and his propagation to other cells.
Alexia F., Doctor in Neurosciences
Sources
– Why are people with allergic asthma less susceptible to severe COVID? sciencedaily.com. Accessed May 3, 2022