Violaine de Saint-André and Darragh Duffy have not yet had time to savor the feat. These two scientists from the Pasteur Institute and the Milieu Interior consortium are conducting interviews with the international media. Normal, when you climb to one of the number of Nature from this week. Their work, which the scientific journal publishes this Wednesday, demonstrates that smoking disrupts the immune system, in addition to attacking the heart and lungs. And this, even after stopping smoking.
The Express. Why were you interested in this subject?
Darragh Duffy: We sought to understand why immune responses were so different from one individual to another. We already knew that there were factors linked to age, sex and genetic heritage. The Covid-19 crisis showed this: people hospitalized, as we know, were often elderly people, and men were, for example, more numerous. We wanted to go further and participate in finding and quantifying the other elements.
Violaine of Saint-André: We were not seeking to demonstrate the effect of smoking in particular, but to test a set of factors that could have had an influence. We quickly realized that smoking had a very significant impact. As important, according to our data, as body mass index, or having cytomegalovirus, a virus from the herpes family, which by nature mobilizes our natural defenses.
How did you do it?
VS-A: We analyzed the blood and secretions of more than 1,000 volunteers. What we sought to quantify was mainly the secretion of cytokines. These are molecules produced in particular by cells of the immune system. They are involved in regulating the system. We focused on thirteen of them. Then we tested the influence of various factors. Smoking contributes 4 to 9% of the variation in cytokine levels.
What does it mean ?
DD: Smoking drastically alters the immune system. As much as age in some ways. This is an important result, because it could have implications on the risk of developing infections, cancers, or even autoimmune diseases. Our study clarifies this risk and, above all, shows that it continues. Some of the changes persist in smokers who have stopped. We see this in particular on the cells of the acquired immune system, the one that learns from contact with pathogens.
In the study, you never say whether the effect is positive or negative. Verdict?
VS-A: We did not test the effect of each component of smoke on immune cells, but smoking in general. And we also haven’t tested how smokers react to all sorts of pathogens and toxins. This is one of the limitations of our study, it does not allow us to specify the effect exactly. But, when we look at the scientific articles on the subject, we do not see any general advantage to such an upheaval of the immune system.
DD: To put it simply, our study shows that smokers are more “inflamed”. This is sometimes a good thing, hence the fact that we refrain from qualifying the effect. It would seem, in fact, that this has reduced the risks of infection with Covid-19, for example. But, overall, it’s a problem. Because once you are sick, having an unregulated inflammatory reaction most often exposes you to very serious consequences. The majority of serious symptoms of Covid-19 are, for example, due to an excessive inflammatory response.
How can we explain these effects on the immune system?
DD: We can roughly say that the body is busy “metabolizing”, digesting, as it were, some of the toxins absorbed when smoking. This leads to modifying the action of certain cells, and also of certain genes, a so-called “epigenetic” effect.
You work for the Pasteur Institute, but also for a lesser-known but scientifically prolific structure, the Milieu Interior consortium. What is his goal ?
DD: Until now, medical practices and health policies have been based on a single patient model, a sort of average patient. With Internal environment, we want to clarify the differences between individuals, understand them, and reveal their influence on different therapeutic approaches. It is a step towards the personalization of medicine.
To do this, we connect researchers from major biomedical research institutions such as the Institut Curie, Inserm, Imagine, Trinity College Dublin, or the École Polytechnique Fédérale de Lausanne (EPFL). One of our strengths is the monitoring of volunteers: we have already been analyzing their blood for 10 years. This is a rare setback in the sector.
.