Consequences for the immune systemThose who smoke are more susceptible to illness
Smoking weakens the immune response - even years after you quit. Researchers show which other environmental factors influence the body's defenses.
Reaching for the glow stick has a similarly strong effect on our body's defense system, such as age and genes. This is what an international research team reports after an extensive study in the journal Nature . The impairment therefore lasts for years even after you stop smoking.
The cold season makes it clear every year: people react very differently to challenges to the immune system. While some people only feel a slight scratchy throat after being infected with a particular virus, others are out of action for days after being infected with the same pathogen. Age, genes and gender play a role in these differences - men are more susceptible to many pathogens - but also changeable environmental aspects such as lifestyle.
Coordination of the immune system
It is precisely these environmental aspects that are the focus of a study led by the French Institut Pasteur, which examined the effects of 136 environmental factors on immune reactions in 1,000 healthy adults. The research group focused in particular on the release of cytokines. These coordinating messengers of the immune system are released when the body encounters pathogens.
To record the respective immune reactions, the team analyzed the production of 13 cytokines in blood samples that were exposed to twelve different immune stimuli. These stimulations triggered reactions in both parts of the immune system: On the one hand, our immune system has an innate part that reacts more generally, and on the other hand, an acquired part, which is built up through diseases and vaccinations and reacts specifically to pathogens.
Of all the environmental factors examined, smoking had the greatest influence on the immune response - and this became more pronounced the longer and the more cigarettes were smoked, explained study leader Darragh Duffy in a press conference. However, the effects on the innate immune defense - including increased inflammatory reactions - were temporary and disappeared again when the smoke was stopped.
However, the effects on the acquired immune response were more persistent: These persisted for many years after quitting smoking and changed the amount of cytokines released during infections and other challenges to the immune system. According to first author Violaine Saint-André, the study primarily contains a message to young people: “Never start smoking,” she emphasized in the press conference.
According to the research group, the cause of the effect of smoking is so-called DNA methylation, a specific epigenetic process in which DNA sequences in the cell nucleus are modified. According to the study, smoking reduces the level of DNA methylation at specific sites, leading to altered cytokine levels in response to immunological challenges.
BMI and viral infections also have an impact
In addition to the use of the glow stick, the main environmental factor that had an impact was an infection with the cytomegalovirus - this herpes virus is widespread worldwide and is considered the most common viral pathogen causing a congenital infection. The body mass index (BMI) also played a role, although the study explicitly included healthy participants - so the test subjects were neither severely overweight nor obese. The researchers therefore suspect that a very high BMI has a greater impact on the immune response.
In a commentary also published in Nature, Yang Luo and Simon Stent from the British University of Oxford emphasize that the study not only provides "a scientific basis for further promoting non-smoking and a healthy lifestyle." It also provides a path toward finding more realistic disease prevention measures, including the possibility of “identifying new molecular signatures of environmental-disease interactions as observed in smokers compared to non-smokers.”
Overall, Luo and Stent said, the work underscores the importance of considering environmental factors—such as smoking, BMI, and viral infections—that play key roles in shaping immune responses. They write: “It is essential to determine how environmental stressors influence epigenetic changes, gene activity and protein function in order to better detect and mitigate the effects of environmental influences on the immune system and to understand the development of environmentally induced diseases.”
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