Electronic cigarettes may weaken the body’s ability to fight infection, found a lab study by VA San Diego and University of California San Diego researchers. Working with both human cells and mice, the team found that e-cigarette vapor interfere with neutrophils, a type of white blood cell. The results suggest that using e-cigarettes could make people more susceptible to and increase the severity of infections, say the researchers.
Based on the findings, Dr. Laura E. Crotty Alexander of the VA San Diego Healthcare System and University of California San Diego, who is the corresponding author on the paper, cautioned against using e-cigarettes. “We recommend that vaping be avoided in general,” she concludes, “as our data and other findings demonstrate multiple possible adverse health effects caused by the use of e-cigarette and vaping devices.”
The results appear in the Jan. 1, 2020, issue of the American Journal of Physiology–Cell Physiology.
Adding to other evidence on harms
Smoking e-cigarettes is often referred to as “vaping.” E-cigarette devices use an electric battery to change a liquid solution containing nicotine into a vapor that can then be inhaled. About 7 to 12% of U.S. adults use e-cigarettes, as well as up to 37% of adolescents and young adults.
E-cigarettes are often portrayed as safer than conventional cigarettes, and some smoking-cessation experts see them as a valuable tool to aid quitting. However, in recent years e-cigarettes have been linked to various breathing problems, including pneumonia, asthma, and bronchitis. The actual safety and impact of e-cigarettes is not well understood. In the new VA-UCSD study, the researchers examined how exposure to e-cigarette vapor affects immune cells to better understand the actual physical effects of the habit.
They did this by isolating human neutrophil cells in the lab. Neutrophils are the most common type of white blood cell in the body, making up 50 to 70% of circulating white blood cells. They play a key role in fighting infection. Neutrophils are attracted to chemicals given off by bacteria cells, allowing them to migrate to the sight of an infection. Once there, they create various compounds to wipe out bacteria cells. Past research has shown that exposure to environmental toxins such as cigarette smoke can make neutrophils less effective.
Hampering white blood cell function
By exposing neutrophils to vapor, the researchers showed that e-cigarettes hamper the neutrophils’ ability both to travel to the site of an infection and to fight it once they are there. Significantly fewer neutrophil cells migrated in response to signals from bacteria after being exposed to e-cigarette vapor.
Exposure to e-cigarette vapor also impeded the neutrophils’ ability to produce bacteria-fighting compounds. Two of the main ways that neutrophils eliminate infections are by producing reactive oxygen species and by generating neutrophil extracellular traps. Reactive oxygen species are chemicals that cause cell damage. Neutrophil extracellular traps are DNA-based structures coated with antimicrobial proteins. E-cigarette exposure interfered with the ability of neutrophils to make either of these products.
While nicotine is known to interfere with neutrophil function, the study revealed that e-cigarette vapor affects neutrophils even without nicotine. The researchers tested e-cigarette vapor that did not contain any nicotine. Neutrophil extracellular trap production was still inhibited when nicotine was taken out. Other ingredients commonly used in e-cigarette solutions, such as propylene glycol, could be to blame.
Results confirmed in mouse model
Crotty Alexander said that based on the lab findings, it appears that “the key chemicals that immune cells are exposed to during vaping cause dysfunction and thus weaken the immune system.”
The researchers confirmed the cell-culture results in a mouse model. Mice exposed to e-cigarette vapor for a month were less able than control mice to fight off bacterial infection. The researchers found fewer white blood cells at infection sites in mice exposed to the vapor. The animal phase of the study provided further evidence that vapor exposure stops the neutrophils from being able to travel.
Taken together, the results provide evidence that e-cigarettes alter the body’s innate immune response on a cellular level, according to the researchers. They say that people who use e-cigarettes may be at higher risk of infections because of these harmful effects.
The research group is continuing to explore the effects of e-cigarette vapor on the immune system. They are currently studying whether the amount or style of vaping affect immune response.
Tristan Horrom/Veterans Affairs