Smoking has lasting effect on immune system which persists even after you quit, finds Nature study

The study, conducted by Pasteur Institute, University Paris Cité, finds that smoking induces changes to DNA that affect the human body’s immune response to pathogens.

Representational image of smoking | Commons

Bengaluru: Researchers have discovered that smoking has long-lasting effects on the immune system and its response for a long time even after quitting. The study analysed 136 environmental factors that contribute to changes in immune responses in 1,000 volunteers and the findings offer insights into parameters that could potentially signify risk of infections, cancer, or auto-immune diseases. 

Of all the environmental factors examined, smoking exerted the most significant influence on immune responses, impacting both innate or immediate and default immunity, as well as adaptive or secondary and specialised immune response.

The study, conducted by Pasteur Institute, University Paris Cité, was published in the journal Nature Wednesday.

The team discovered that effects on innate, generic responses disappeared a few days after quitting smoking, but the altered levels of adaptive response persisted for many years after quitting. 

While it is generally common knowledge that smoking leads to ailments like cancer, the findings provide further scientific evidence to promote a healthy, non-smoking lifestyle, say the authors. 

Human immune response

Immune cells patrol our entire body, constantly scanning for foreign objects. Once identified, these cells signal to the immune system to mount an attack. 

The first defence occurs in the form of a generic immune response, called the innate immune response. As the immune cells from the innate response come in contact with the foreign particle, they transmit the information back to the immune system, which prepares to build a more customised response that could precisely target the invading pathogens.

This secondary response, which sets in after a few days, is called the adaptive response and is responsible for destroying foreign particles or viruses in our bodies. 

The adaptive response is also memory-based, and stores information about a pathogen to mount a quick attack in the future. 

The proteins that are responsible for signalling between immune cells are called cytokines. The production of cytokines varies from person to person and is dependent on both genetic as well as environmental factors. 

To measure the effectiveness of immune responses, the production of 13 disease-associated cytokine proteins was studied by the team, upon exposure to 12 different pathogens. 

Study methodology

The authors enrolled 1,000 healthy individuals as volunteers in their study and examined 136 factors that could contribute to variation in cytokine production. These factors were environmental and included diet, lifestyle, and socioeconomic demographics.

Of these, the scientists discovered three particular factors were mainly responsible for changes in cytokine production and response — the body mass index, a measure of body fat based on one’s height and weight, smoking, and a latent infection by a virus called cytomegalovirus. 

When immune stimulations such as antigens (part of foreign particles/pathogens/bodies) were exposed to blood samples in the lab, various types of immune responses arose. Of these, smoking was found to have a transient or temporary effect on innate immunity but persisted in its effect on adaptive immunity despite cessation of smoking. 

To investigate why, the authors looked for epigenetic changes, or the changes caused to our genes that change their behaviour. 

They found that a process called DNA methylation was affected in the cells associated with the adaptive immune system due to smoking. Methylation helps in expressing or turning on and off certain genes. The data indicated that smoking decreased the level of DNA methylation at certain sites in the cells of the immune system. 

Cytokines

The team noted that affected cells were associated with metabolism and signalling processes in the body, and the lowered levels of DNA methylation led to variability in the levels of cytokines. This was particularly true for a cytokine called CXCL5, which increases the level of a protein called CEACAM6 in the bloodstream of a smoker. 

This protein is associated with immune regulation as well as inflammation in the body. It is also thought to be a clinical biomarker for some types of cancers. 

The authors highlight that the effects of this cytokine, the CEACAM6 protein, and smoking on other aspects of the immune system need to be studied more. The study also states that while many aspects of our immune system and immune response are dependent on factors like age or genetics, environmental factors like smoking also play a key role.

(Edited by Uttara Ramaswamy)