The coronavirus epidemic taught us a valuable lesson about individuals' unique defenses against illness. Some afflicted people died within days of becoming infected, while others were unaware of it.
A little more than ten years ago, Spanish biologist Lluís Quintana-Murci and his American colleague Matthew Albert began an audacious experiment to investigate the factors that drive this unpredictability.
In the French city of Rennes, they gathered 1,000 fit individuals between 20 and 70, selecting 100 volunteers of each gender for every decade. They all completed a 44-page questionnaire on their lifestyles and gave samples of their blood and feces. Even skin biopsies were performed to cultivate their cells in a lab.
This Wednesday, the most recent findings will be revealed: smoking, even years after quitting, is the element that most modifies defenses.
The World Health Organization lists over 100 reasons to abstain from tobacco use, including increased risk of heart attack or cancer, unpleasant body odor, high annual costs (over 1,800 euros for daily smokers), wrinkles on the face, yellow teeth, and harm to those who are around secondhand smoke.
Tobacco contains harmful compounds that weaken the immune system and raise the risk of infections, cancers, autoimmune illnesses, and AIDS, as explained in reasons 79, 80, 81, and 82. The new research cautions that the alterations in the white blood cells of former smokers can last for years, as it was published on Wednesday in the journal Nature.
Of the 136 factors examined, the environmental component had the most impact. It is followed by body mass index and latent CMV infections, which are known to have negative effects on one in five afflicted babies.
The Pasteur Institute in Paris is home to the study's authors, who have concentrated on the synthesis of cytokines, which are proteins secreted by cells in response to pathogen detection and which aid in the coordination of the immune response.
The scientists, under the direction of immunologist Darragh Duffy and biologist Violaine Saint-André, have found that smoking alters our innate non-specific defenses, resulting in increased inflammatory reactions. The negative effects vanish when you give up smoking.
Scientists have found, however, that years after quitting smoking, the cells that are responsible for lifelong specific immunity do not return to their original state. The only factor whose effects are equivalent to those of immutable factors like age, sex, and genetics is smoking.
Although cautious, the researchers maintain that their findings "have potential clinical implications on the risk of developing infections, cancer, and autoimmune diseases." The connection between malignancies and this change in white blood cells has not yet been investigated.
But as Duffy notes, "smoking raises the risk of multiple types of cancer, as is well known from much other previous work; the longer you have stopped smoking, the lower the risk." The immunologist references a recent study conducted in South Korea with over three million participants, which found that after 15 years of stopping smoking, the risk of cancer decreased by 50%.
To facilitate a study in a genetically homogeneous population, the 1,000 participants in Rennes are descended from Western European forebears.
However, the scientists are already working on comparable trials in other locales, including Senegal and Hong Kong. Born in Palma de Mallorca 53 years ago, Lluís Quintana-Murci has spent over 20 years working in Paris.
Marcos Lopez Hoyos, the president of the Spanish Society of Immunology, praises the recent research, in which he was not involved. He notes, "We have always seen a clinical finding: we found hypogammaglobulinemia [low levels of antibodies], which is a cause of secondary immunodeficiency in many patients with chronic smoking and COPD [chronic obstructive pulmonary disease]."
Smoking increases the risk of infections and cancer in people with COPD. Although they cannot prove it, the cytokine alteration they have seen strongly suggests that it may favor changes in immune response regulation and result in these diseases, according to López Hoyos, scientific director of the Marqués de Valdecilla Research Institute in Santander. He exclaims, "It's an incredible study."
Oncologist Alberto Ocaña describes the latest results as "very interesting, but not surprising," but he cautions about them. The study does not prove that immune system modifications brought on by tobacco use cause cancer. Coordinating the Experimental Cancer Therapies Unit at the San Carlos Clinical Hospital in Madrid, Ocaña says that although cancer is a genetic disease, it also needs other changes, such as a malfunctioning immune system.
The Pasteur Institute team has cultured volunteer cells, exposed them to various compounds in the lab, and observed their behavior. The length of the effects of smoking surprises África González, a University of Vigo immunologist. The immune system's continued maintenance of this signal, which seems to be saying, "You have smoked," is startling.
Additionally, those cells will react differently to a disease after being exposed to tobacco, she muses. "They cannot definitively state that this modification raises your risk of cancer, but tobacco contains numerous compounds that are carcinogenic in and of themselves, in addition to changing the immune system," González cautions.