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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 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 from the Institut Pasteur, Université Paris Cité, Paris, France and others investigated the effects of 136 environmental factors on variability of immune responses in 1,000 individuals. 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. “The results collectively show a short-term effect of smoking on innate immune responses, and a long-term effect of smoking on adaptive immune responses,” they write.
“Our study identifies a strong link between these previously proposed disease biomarkers and response to immune challenges in smokers versus non-smokers. Furthermore, our findings in healthy donors open avenues for further exploration into understanding how smoking acts as a risk factor for cancers beyond the lungs,” they write.
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 cannot be changed, such as age, sex and genetics.
The authors acknowledge some limitations in the 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.
