Allergies better equipped against Covid-19?

Researchers suggest people with asthma would be protected from the coronavirus. However, there are still some gray areas.

Illustration of a grass pollen allergy @BelgaImage

That was the big question when Covid landed: are allergy sufferers more susceptible to Covid-19 or not? More than two years after the beginning of the pandemic, the first reactions are emerging. This is particularly evident from a study in the journal The Lancet Respiratory Medicine and another from PNAS, published by the American National Academy of Sciences. If we had to summarize the answer, it would be: It depends.

Cells that barricade themselves better

PNAS’s is the most reassuring. It turns out that only about 5% of asthmatics, in this case those with severe asthma, are more likely to be serious Covid-19 patients. The others, on the other hand, might be better equipped to face the disease. A real paradox that has intrigued researchers. “We knew there had to be a biomechanistic reason that could explain why some asthmatics appeared to be protected from severe Covid.‘ explains the study’s author, Camille Ehrlich, in Science Daily.

So his team went in search of what it was. To do this, they examined the mechanisms of the respiratory system, which are affected by both Covid-19 and asthma. In the case of the coronavirus, it is its spike proteins that allow it to attach to human cells via the ACE2 receptor. To protect themselves, these cells have a defense mechanism known as mucin MUC5AC. Problem: When the invasion is too large, the proteins responsible for it become overwhelmed. The amount of MUC5AC mucin becomes insufficient and the coronavirus thrives.

However, in people with asthma, mucin MUC5AC is overproduced due to the presence of interleukin 13 (IL-13), the mediator of allergic inflammation. Logically, therefore, thanks to this anti-Covid barrier, they are better prepared for the coronavirus. Even better, IL-13 also reduced production of the ACE2 receptor, further limiting the chances of infection and then spreading to surrounding cells. In summary, the respiratory system is barricaded. Laboratory experiments using IL-13 on human lung cells confirmed this hypothesis. A track on the development of new treatments against Covid-19. “This study demonstrates the importance of certain specific mechanisms involving the expression of IL-13 and how this could be used to protect patients and prevent the development of severe forms of Covid‘ says Camille Honor.

Some asthmatics are much more susceptible than others

However, the researcher acknowledges that there are still gray areas as to the exact mechanism of IL-13. Which protects more: MUC5AC mucin production or ACE2 receptor reduction or a mixture of both? Then the use of IL-13 as a drug is ruled out as such, since it would cause inflammation in people who already suffer from this problem. Finally, there are still people with asthma who react very strongly to the coronavirus.

Among those who are particularly sensitive to Covid-19 are at least some children. This is the subject of the Lancet study. To show this, the researchers looked big, with a cohort of 750,000 children aged 5 to 17. 5.8% of them contracted Covid and 0.9% were hospitalized. Among the 63,000 asthmatics included, these rates rose to 6.8% and 1.5%, respectively. But one child with asthma is not the other. Again, patients with severe asthma were the most likely to end up in hospital, at 548 cases per 100,000, compared with 94 per 100,000 among other asthmatics.

This study partly explains why asthma generally did not appear as a risk factor for the severe form of COVID-19 in some studies, because it is a risk factor that is only really significant for a subset of asthmatics. [ceux dont la maladie n’est pas contrôlée] and not necessarily for all asthmatics“, explains the Quebec newspaper Le Devoir Dr. Jesse Papenburg, pediatric microbiologist-infectiologist at the Montreal Children’s Hospital. According to her, we must therefore remain cautious about the a priori similar number of hospitalized Covid asthmatics and non-asthmatics. In addition Containment may have encouraged people to protect themselves against allergens as well, which can skew the numbers.

Leave a Comment