Fear and stress make the immune system vulnerable Company | DW

That stress is harmful to health should not surprise anyone. It is well known that psychological stress and anxiety can have a direct impact on the human immune system, making us more prone to disease. It has been less clear so far how this system works.

Wolfram Poller, a cardiologist and researcher at the Charité Clinic in Berlin and the Icahn School of Medicine in Mount Sinai, New York, was able to show, along with several researchers, in a study on mice that certain regions of the brain are responsible for the crucial change of leukocytes in the body. They determine how sensitive an organism is to viral infections.

Stress really makes us sick

“The most interesting thing for me was to see the terrible impact that several hundred neurons in the hypothalamus have on millions of leukocytes throughout the body,” says Poller.

Neurons set in motion a complex sequence of interactions between three hormonal glands, the hypothalamus, the pituitary gland and the adrenal cortex. This so-called stress axis controls many reactions to stress in our body.

Poller and colleagues conducted the study on mice. Some of the mice were repeatedly exposed to stressful situations. The animals were locked in a cylinder, moved to a new cage or exposed to the smell of urine from natural predators.

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The researchers noticed that certain leukocytes in these mice retreated into the bone marrow and, simply put, did not do their job. This made stressed animals particularly vulnerable to Covid or influenza infection. Not only did the animals become seriously ill much faster, but they also died more often.

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Leukocytes, granulocytes and lymphocytes

Leukocytes are also called white blood cells, which form in the bone marrow and perform various functions in the immune system. Among the leukocytes are granulocytes, involved in non-specific immune defense. In the event of a lesion, they can fight invading bacteria and parasites, but without being specifically responsible for a pathogen.

On the other hand, lymphocytes, which are also part of the category of white blood cells, are specialized. These include T and B cells, which specifically target certain antigens, ie proteins of a pathogen, making it harmless. In the case of Covid, these include the already well-known spike proteins.

Stress pushes lymphocytes into the bone marrow

Poller and his team noticed that these lymphocytes simply withdraw under stress. Normally, lymphocytes are located in the so-called lymphatic organs: the spleen, thymus or lymph nodes. In stressed mice, they retreated into the bone marrow.

Poller cannot say with certainty whether this mechanism is valid in the same way in humans. However, the axis of stress that has become active in mice also exists in humans. Researchers believe that fear and stress can make the human immune system vulnerable, which becomes more prone to viral diseases.

The concentration of granulocytes increases

In addition to the withdrawal of lymphocytes in stressful situations in the case of viral infections, a phenomenon also occurs in the body. At least in the organisms of the mice that Poller and his colleagues studied, there was an increase in the number of granulocytes shortly after the mice were stressed.

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The fact that this first non-specific defense of the immune system is activated in a situation of great fear, which can result in running or fighting, is perfectly logical. “The body is thus prepared for a possible injury,” explains Poller.

Does stress decrease the effectiveness of vaccination?

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The researcher is considering conducting another study, this time with people, but without deliberately scaring them. On the contrary, the idea would be for them to reach a particularly balanced state with stress reduction measures, and then for the researcher to vaccinate them against Covid.

The data collected from the study on mice give the researcher something to think about. “If a weaker specific immune response to a Covid infection develops under stress, a virus vaccination may also result in a weaker immune response if the person is stressed. Or, in case of a vaccination, you want to get a strong immune response “, says the expert.

The production of specific antibodies and T cells would be inhibited due to stress, and the risk of reinfection and disease would increase considerably. Poller points out that, although there is no data yet to directly support this hypothesis, one thing can be said with relative certainty: reducing stress does no harm!