It is common knowledge that stress and fear can have a direct effect on the human immune system - making us more susceptible to disease. However, until now it was unclear exactly how this mechanism works.
Together with a team of researchers, Wolfram Pohler, a cardiologist and researcher at the Charite University Clinics in Berlin and Mount Sinai School of Medicine in New York, succeeded in a mouse study to show that certain regions of the brain are responsible for the key movement of leukocytes in the body - and therefore and how susceptible the organism is to viral infections.
Stress really makes us sick
"What was most exciting for me was seeing the enormous impact of a few hundred neurons in the hypothalamus on millions of leukocytes throughout the body," says Poehler.
Neurons trigger a complex set of interactions between the three endocrine glands, the hypothalamus, pituitary gland, and adrenal gland. This so-called stress axis controls many stress responses in the body.
Poller and his colleagues conducted research on mice, some of which were repeatedly exposed to stressful situations. Animals are locked in a cylinder, moved to a new cage or exposed to the smell of urine from natural enemies.
The researchers noticed that certain leukocytes in the mice retreated into the bone marrow and - simply put - were no longer doing their job. Because of this, stressed animals were particularly susceptible to infection with SARS-CoV-2 or influenza. Animals not only got sick faster, but also died more often.
Leukocytes, granulocytes and lymphocytes
Leukocytes are called white blood cells. They are formed in the bone marrow and have various functions in the immune system.
Leukocytes also include granulocytes, which are part of the non-specific immune system. In case of injury, they fight against bacteria and parasites that enter the body, but they are not specialized for any specific pathogen.
Lymphocytes, on the other hand, which also belong to white blood cells, are specialists. They include T and B cells, which target specific antigens, or pathogen proteins, and render them harmless. In the case of SARS-CoV-2, this includes the now well-known spike proteins.
Stress drives lymphocytes into the bone marrow
Poler and his team noticed that these lymphocytes retreat in stressful situations. It is normal for lymphocytes to be found in the so-called lymphatic organs: spleen, thymus gland or lymph nodes. In stressed mice, they retreated into the bone marrow.
Poler cannot say for sure whether this mechanism can be transferred to humans in the same way. But the stress axis that became active in mice also exists in humans. It is therefore obvious to the researcher that fear and stress can also make the human immune system more susceptible to viral diseases.
The concentration of granulocytes increases
As much as the withdrawal of lymphocytes is unfavorable in stressful situations in the case of viral infections, something else happens in the body - at least in the mouse bodies that Poller and his colleagues studied: they noticed an increase in granulocytes shortly after the mice were stressed.
It is perfectly logical that this first, non-specific defense of the immune system is activated in a situation of great fear, from which flight or fight can arise. "That's how the body is primed for injury," says Poehler.
Does stress reduce the effect of vaccination?
The researcher is therefore considering another study, this time with humans. However, they should not be deliberately scared, but - on the contrary - with measures to reduce stress, achieve a particularly balanced state.
Then he wants to vaccinate them against covid-19. Poler has a hypothesis that derives from data collected in a mouse study: "If a weaker specific immune response to SARS-CoV-2 infection develops under stressful conditions, then a weaker immune response may also occur under stress when vaccinating against the virus. And in the case of vaccination, you want to achieve a strong immune response."
The formation of specific antibodies and T cells is inhibited due to stress and the risk of re-infection and disease is higher. Data that directly support this hypothesis do not yet exist, emphasizes Poler. However, it can be said with relative certainty: Less stress is not bad for health.
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