The immune system's function is to protect the body against infections caused by pathogens and, at the same time, must maintain tolerance towards the components of the body itself. For this reason, this system has developed a whole set of very varied responses appropriate to combat the different aggressors without damaging the cells themselves.
- 1 Physiology of the immune system
- 2 Psychoimmunology
- 3 Inhibition of the immune system against stress
- 4 Neural control of the effect of stress on the immune system
- 5 Stress and pathology of the immune system
Physiology of the immune system
In order to defend the body from infections, the pathogen must first be recognized and the most appropriate response can be established to destroy it. The immune system has two types of defense mechanisms:
- Innate immunity, mechanism based on a nonspecific response to tissue injury by an invading organism, by which blood circulation is increased, an inflammatory response is produced and an attempt is made to destroy the pathogen.
- Adaptive immunity, where two types of specific reactions occur: one generated by cells and the other chemically directed.
The immune system has two mechanisms of reaction to aggression: a rapid and nonspecific response and a later response, but with a high degree of specificity.
Psychoimmunology is the discipline that studies the interactions between the nervous system, the immune system and the endocrine system, analyzing how psychological factors can influence the general state of health of a person.
"First of all the accumulation of data that were emerging about the relationship between the neuroendocrine system and the immune system, I decided to put a sign on the laboratory door that read: Laboratory of Psychoimmunology. "GF Solomon (1963)
This discipline was developed thanks to three triggers:
- Riley and colleagues demonstrated that psychological stress in animals increased morbidity and mortality due to experimentally induced tumors.
- Different studies showed that stress and anxiety were able to decrease the response of the immune system and increase the likelihood of infectious diseases.
- In the 1980s, Robert Ader and Nicholas Cohen demonstrated that immunosuppression can become a conditioned response.
Ader (1981) was investigating taste aversion, applying a drug that produced a stomachache to rats that ingested water with saccharin. Rats generated a dislike of the taste of sweetened water. Ader extinguished this conditioning by exposing the rats to water with saccharin without the drug, during several tests. Approximately one month later, some animals died, since the drug, in addition to producing a stomachache, generated immunosuppression. Therefore, Ader managed to condition the immune response, since the presence of sweetened water alone was able to suppress the immune response.
Immune tissue is sensitive to many hormones that are secreted by the pituitary gland under neural control.. Probably one of the clearest examples of the influence of the nervous system on the immune system is the conditional immunosuppression paradigm.
In 1982, Ader and Cohen studied a species of mice that developed spontaneous diseases due to immune hyperactivity. These researchers demonstrated that by means of classical conditioning techniques they could substitute an immunosuppressive drug (to control this excess of immune activity) with a conditioned stimulus and thus modify the immune system of the animals.
Inhibition of the immune system against stress
It has been found that stress alters the formation of new lymphocytes, and also their secretion into the bloodstream. Several studies have also shown that the stress response decreases the creation of antibodies in response to an infectious agent. Likewise, communication between lymphocytes through the release of messengers remains very depleted by stressful stimuli.
Apparently, The stress response increases the level of secretion of glucocorticoids, hormones that depress immune system activity.
Glucocorticoids cause a reduction of the thymus gland, stop the formation of new T lymphocytes and inhibit the secretion of interleukins and interferons. They also reduce the sensitivity of lymphocytes to the infection alarm. These hormones have the ability to enter lymphocytes to secrete a protein that breaks their DNA.
Although many aspects of immunosuppression in response to stress can be explained by the action of glucocorticoids, not all effects depend on these hormones.
Neural control of the effect of stress on the immune system
The neurons of the central nucleus of the amygdala project towards the neurons that secrete CRF from the paraventricular nucleus of the hypothalamus; For this reason, it is logical to think that the negative emotional response is closely related to the stress response and immunosuppression.
Several studies hypothesize that immunosuppression that is not due to glucocorticoid secretion could be under direct neural control, since both the thymus gland and the bone marrow and lymph nodes receive neural inputs.
The immune system is sensitive to many substances secreted by the nervous system.
Shavit et al. Observed that an intermittent electrical discharge that was inevitable produced a reduction in pain sensitivity and a suppression of the production of NK cells (natural killers) from the immune system to experimental animals, by the release of endogenous opiates.
The nervous system can directly regulate the effect of stress on the immune system.
Stress and pathology of the immune system
Several studies have shown that a wide variety of stressful stimuli can increase the susceptibility to suffer certain pathological processes, such as infectious and / or autoimmune diseases.
Feigenbaum, Masi and Kaplan in 1979 observed, for example, that autoimmune diseases worsen when the subject is under stress.
It has been found that stress affects the course of some types of cancer:
Stress can induce tumors to grow faster.
The immune system has a type of cells (natural aggressor cells or NK) that prevent tumors from becoming extinct, but stress prevents these cells from circulating in the blood.
Tumor processes require a lot of energy for their development. The stress response facilitates the availability of blood glucose, thereby influencing the growth rate of a possible tumor.
Trujillo, H. M., Oviedo-joekes, E. & Vargas, C. (2001). Advances in psychoneuroimmunology. International Journal of Clinical and Health Psychology / International Journal of Clinical and Health Psychology, 1, 413-474
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