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Smoking has a lasting effect on specific human immune responses, persisting long after quitting, reports a paper in Nature this week. The study, which investigates a range of factors that might contribute to variability in immune responses, also identifies body mass index (BMI) and latent infections of cytomegalovirus (a common virus) as having a substantial influence on immune responses. The findings may offer insights into the factors that potentially underlie the risk of developing infections and other immune related illnesses such as cancer or auto-immune disease.
There is wide variability in the way humans respond to immune challenges, such as bacterial or viral infections, as seen with the diverse range of clinical outcomes observed after infection with SARS-CoV-2. Age, sex and genetic factors play a major role in this variability, but modifiable environmental factors, such as lifestyle, may also contribute. Understanding how such variables affect immune responses could improve the design of treatments and vaccines.
Darragh Duffy, Violaine Saint-Andre and colleagues investigate the effects of 136 environmental factors on variability of immune responses in 1,000 individuals. They look specifically at the secretion of cytokines, proteins released when the body encounters a pathogen, which have a role in coordinating the immune response needed to fight the pathogen. Among the environmental factors studied, smoking was shown to have the greatest influence on immune responses. It affected both innate and adaptive immunity—the former is a general response whereas the latter is more specialized and pathogen-specific. While the effects on innate responses (such as increased inflammatory responses) were transient and lost after smoking cessation, the effects on the adaptive response persist for many years after quitting, altering the levels of cytokines released upon infection or other immune challenges.
BMI and cytomegalovirus are also found to have noteworthy effects on cytokine secretion, but the variance associated with smoking reaches levels equivalent to those linked to factors that we cannot change, such as age, sex and genetics. Duffy and colleagues acknowledge some limitations to their study, such as the absence of a replication cohort and limited genetic diversity in the individuals studied. However, the findings provide new insights on the impacts of smoking on human health and help our understanding of the role that modifiable environmental factors have on immune response variability. These findings provide “a scientific basis for further promoting non-smoking and a healthy lifestyle”, write Yang Luo and Simon Stent in an accompanying News & Views
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Professor Chris Bullen, School of Population Health, University of Auckland
This paper adds to the very large body of evidence accumulated over decades that shows smoking is bad for people’s health and why quitting smoking if you do smoke is beneficial – and even better yet, why never smoking in the first place is the best option.
The popular understanding of the harms of smoking has tended to focus on lung cancer and chronic lung diseases like emphysema. But many other cancers – for example, oesophageal, stomach and ovarian cancer - are also more common in people who smoke. People may not be aware that smoking also promotes blood vessel disease, causing heart attacks, stroke, aortic aneurysm, and peripheral vascular disease. Smoking also increases people’s risk of developing common conditions like diabetes and developing some serious infectious diseases like tuberculosis and meningococcal disease.
New insights, such as this paper provides, point to the immune system as a common pathway through which such a diverse range of diseases may be triggered and sustained by smoking.
The good news is that it suggests most of the immune system changes are reversible when people quit smoking. This new information could be just the motivation for people who smoke to stop smoking once and for all.
But to help them succeed, we need more than just good intentions. Smoking is not only deadly, it is also addictive, and tobacco is far too widely available for such a harmful product. Therefore, we need supportive policies that make smoking far less addictive, accessible and acceptable. That is why the evidence-based policies in the current Smokefree Act that our new coalition government seems determined to repeal – removing nicotine from tobacco, reducing retailer numbers, and making it illegal to sell this dangerous, toxic product to future generations - are so important to retain.
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