How the immune system responds to an infection depends greatly on an individual’s genes, gender and age. But smoking is just as important as a factor, researchers from the Institut Pasteur conclude this week Nature. By eliciting immune responses in blood samples, the French researchers looked for environmental factors that influence the immune system.
Tobacco smoking affects the innate immune system for a short time, but can also cause long-term changes in the learned part of the human defense, the team writes. This learned or acquired immune system clears pathogens with the help of antibodies and immune cells. Regular smoking can alter the function of certain genes in the DNA, causing the acquired immune system to react more strongly to pathogens and potentially pose health risks.
Small proteins
For the study, the researchers took blood and data from a thousand healthy people between the ages of 20 and 70. They exposed the samples for 22 hours to eleven different pathogens, antigens and other substances that trigger a response in the immune system, and then looked at the amount of cytokines produced. These are small proteins that coordinate the body’s immune response. Finally, the cytokines were compared to a survey of 136 different clinical and environmental factors.
A difference in the immune response was found for eleven of the variables. The body mass index (BMI) and the cytomegalovirus, a dormant herpes virus, were found to influence the levels of cytokines in two of the substances. But by far the largest difference in cytokine production was found between smokers and non-smokers.
An enhanced immune response in the innate immune system – the body’s first and most general line of defense – was found in active smokers. By exposing the defenses of this group to the bacteria Escherichia coli, higher amounts of the cytokine CXCL5 and the protein CEACAM6 were found. These substances can induce inflammation and play a role in lung diseases and various forms of cancer. People who had stopped smoking for some time no longer produced these proteins.
The acquired immune system, on the other hand, was affected for much longer. After adding an antigen of the bacteria Staphylococcus aureus (SEB), high cytokine levels were found in the blood of both active smokers and ex-smokers who had quit ten to fifteen years earlier.
According to the research team, the fact that the immune system remains influenced for so long by cigarette smoke is due to epigenetic changes. Molecules attach themselves to the DNA at specific locations and thus influence the activity of genes, such as the genes involved in the immune system. The research shows that tobacco smoke actually detaches these molecules from the DNA, including genes that are linked to certain lung diseases. The changes in DNA became more dramatic with the number of cigarettes smoked and the number of years the participants had smoked in total. Stopping smoking slowly reverses the epigenetic changes.
The researchers therefore strongly recommend that you stop smoking. The study did not directly look at the effect of tobacco smoke on the health of the participants. The study does provide insight into how it causes the diseases it has been associated with for so long, says study leader Darragh Duffy of the Institut Pasteur at a press conference about the research. “The overactive immune system that we now see in smokers may explain why they often suffer from immune system diseases and chronic conditions.”
Together with his colleagues, he has started a follow-up study in which they will follow some of the people again for a long time. In this study, the immune responses are also compared with the health of the participants.