It's widely accepted that smoking weakens the body's immune defenses, with tobacco affecting the "innate" and "adaptive" responses. The "innate" response responds quickly when confronted with an invader (microbes, toxins), while the "adaptive" response is slower to intervene. This latter response is more powerful and better targeted and mobilizes specialized cellular forces that are trained to eliminate an enemy that has already been encountered.

In smokers’ lungs, several types of immune cells are damaged: Damage to the alveolar macrophages aggravates airway inflammation. Damage to cytotoxic T lymphocytes promotes the destruction of the lining of the pulmonary alveoli.

But what about former smokers? Even several years after quitting smoking, their adaptive immune responses remain impaired, a team from the Institut Pasteur revealed in the journal Nature on Thursday, February 15.

The authors analyzed data from 1,000 healthy individuals between the ages of 20 and 70, half were men and half were women. This was the "Milieu intérieur" ("Interior Environment") Consortium, set up in 2011. "Our aim was to gain a better understanding of the variability of immune response in healthy individuals, according to lifestyle or sociodemographic characteristics," explained Violaine Saint-André, a bioinformatician at the Institut Pasteur and the study’s first author. It acts as a reference map, in short, for a better understanding of pathological situations.

Persistent disruption

Participants answered a questionnaire about their lifestyles, and their immune responses were unraveled using samples of their blood, which contains immune cells. The authors exposed these samples to a wide variety of microbes (influenza virus, bacteria E. coli, fungus C. albicans) and molecules known to stimulate innate or adaptive immune responses. They then quantified the levels of 13 "cytokines", proteins released by immune cells on encountering a pathogen, which play a key role in coordinating the immune response.

The authors looked for the variables that had the greatest impact on immune responses, among the 136 selected (body mass index, smoking, hours of sleep, physical activity, childhood illnesses, vaccinations). They did this independently of age or gender, factors known to influence immunity.

Smoking showed the most notable impact. The study confirms that active smokers have an innate inflammatory response that is 50% higher, on average, than non-smokers. Their adaptive immune response, on the other hand, appears to be exaggerated by an average of 10% to 30%. These disturbances are proportional, however, to the number of cigarettes smoked and years of smoking.

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