Study investigates how stress due to sleep deprivation affects immunity

To achieve a deeper understanding of the links between the nervous and immune systems, researchers at the Federal University of São Paulo inhibited the REM stage of sleep in mice to see how this affected the progress of infectious diseases, allergic processes and cancer treatment.

By Janaína Simões  |  Agência FAPESP – With the aim of analyzing the relationship between the nervous and immune systems, a research group led by scientists at the Federal University of São Paulo (UNIFESP) in Brazil investigated the impact of sleep deprivation on the immune response in three situations: allergic asthma, malaria, and immunotherapy against tumors. To this end, they induced rapid eye movement (REM) sleep disturbances in mice. REM sleep is the most important phase of sleep for rest and a balanced metabolism.

In one series of experiments, the group set out to discover whether the stress caused by sleep deprivation could affect natural immunity during the process of developing malaria. In another study, they focused on its impact on cancer treatment using an immunotherapeutic developed by a Japanese firm. In a third, the aim was to find out whether stress could exacerbate a pre-existing inflammatory disease such as asthma.

“The main purpose of all these studies was to deepen our understanding of the two-way relationship between the nervous and immune systems, as a contribution to the development of novel treatments for inflammatory diseases and neurological disorders, as well as immunotherapy and immunoprophylaxis,” said Alexandre Keller, a professor at UNIFESP’s Medical School.

Keller and Daniela Santoro Rosa, both of whom are professors in the Department of Microbiology, Immunology and Parasitology, coordinated the research, which was conducted in partnership with Monica Levy Andersen, a professor in the Department of Psychobiology. The work was funded by FAPESP via four research grants (2012/04692-1; 2014/15061-8; 2017/17471-7; and 2019/11490-5).

Immunosurveillance against tumors

Several studies have found that stress impairs immunosurveillance against tumors, but its influence on the activities of natural killer T cells (NKTs) is poorly understood. These T lymphocytes influence several types of immune response including immunosurveillance, and hence interest scientists who aim to develop a treatment for cancer.

The research group used an experimental model of pulmonary metastasis to estimate the effects of sleep deprivation on immunotherapy with alpha-Galactosylceramide, a synthetic glycolipid used in clinical trials (outside Brazil) against several types of cancer. “The animals were inoculated with melanoma cells that express this glycolipid on the surface, and then exposed to sleep deprivation,” Keller said. “Until now, the efficacy of this approach has proved excellent in mice but less so than expected in humans, and we don’t know why.”

A possible explanation is the effect of stress, and the researchers are the first to study the impact of sleep disorders on the efficacy of the immunotherapeutic.

According to Keller, even with an increase in corticosterone (the stress hormone in animals, equivalent to cortisol in humans), the response induced by alpha- Galactosylceramide was sufficient to control tumor growth. “Our work shows that these cells in this model aren’t affected by stress, so in theory, they continue to be a relevant target for immunotherapy even during stress episodes,” he said. The findings are reported in an article published in Brain, Behavior, and Immunity. 

Defense against pathogens

Another question the researchers wanted to answer was how sleep disorders affect the organism’s natural response to pathogens. To do so, they analyzed protozoans of the genus Plasmodium that cause malaria and are transmitted by the bite of the female marsh mosquito (Anopheles spp). “We showed that the efficacy of the antibody response diminishes if sleep disturbance occurs at a particular point of the process whereby the natural response to the pathogen develops,” Keller said. 

Using a murine model of malaria in which antibody production plays a key role in host survival, they observed the development of the immune response in a time curve known as the immune window. Sleep deprivation was imposed in different periods. Before and shortly after infection, it did not affect the host’s resistance to the parasite, but when it occurred three days after infection the animals died. 

The critical point in the process, according to the researchers, is the start of the adaptive immune response, when T lymphocytes act in conjunction with B lymphocytes to stimulate the production of antibodies.

“We were able to observe that if a stress episode occurs during the T lymphocyte differentiation stage, a process that leads to activation of B lymphocytes and production of antibodies, the efficacy of the response is diminished and the organism becomes more susceptible to infection,” Keller said.

The article “Sleep disturbance during infection compromises Tfh differentiation and impacts host immunity”, describing the study and its results, is published in iScience. 

Sleep deprivation and asthma

To estimate the impact of sleep deprivation on a pre-existing inflammatory disease, the researchers studied allergic asthma, which can range from intermittent to persistent and severe. Severe asthma patients have high levels of neutrophils and are often refractory to treatment with corticosteroids, and this kind of clinical manifestation has been associated with various comorbidities, including obstructive sleep apnea, in which breathing stops involuntarily for brief periods of time during sleep.

The study showed that sleep disorders can increase the severity of the inflammatory response in mice, so that mild asthma may progress to severe asthma owing to lack of sleep, and may even become resistant to treatment with corticosteroids.

To arrive at this result, the researchers used an experimental model of allergy in which mice were induced to develop a response involving Th2 lung inflammation with a predominance of eosinophils (a type of white blood cell that plays an important role in the response to asthma and other diseases), and cytokines such as IL-4 and IL-13, which activate, mediate or regulate the immune response. When they were submitted to sleep deprivation during exposure to the allergen via the airways, the animals’ Th2 inflammatory response changed to Th17, in which neutrophils and IL-17 predominate, and which is resistant to treatment with the corticosteroid dexamethasone.

Although the mechanisms that produce this phenomenon are not yet fully understood, the study suggested that sleep disorders, and possibly other stress situations, are risk factors for the development of severe allergic asthma. An article reporting the study is published in The Journal of Allergy and Clinical Immunology. 

These studies are part of a larger set of ongoing projects that focus on a wider and deeper understanding of the two-way relationship between the nervous and immune systems. “If immunotherapy doesn’t work because of the strong influence of the nervous system, it may be possible to target the neurotransmitters or receptors, for example,” Keller said.

In other words, their findings may not have immediate applications in clinical practice, but the knowledge obtained will serve as a basis for future interventions. “The more we understand how stress affects the immune system, the more strategies we can design to act on the immune or nervous system for the purposes of medical treatment,” he summed up.