Chapter 8: Immunity, Stress, and Disease

Psychoneuroimmunologist: someone who studies the fact that what goes on in your head can affect how well your immune system functions

There is a strong link between the nervous system and the immune system

• Example: Give an animal a drug that suppresses the immune system, along with a conditioned stimulus (e.g.: artificially flavored drink). A few days later, present the conditioned stimulus by itself—and the immune function goes down

The immune system

• Its primary function is to defend the body against infectious agents such as viruses, bacteria, fungi, and parasites
• Immune defense is carried out by white blood cells called lymphocytes and monocytes
• Lymphocytes: consists of T cells and B cells
• T cells: originates in the bone marrow but migrates to mature in the thymus. Has several functions (T helper and T suppressor cells, cytotoxic killer cells, and so on)
• B cells: originates and matures in the bone marrow. Produces antibodies
• If the immune system confuses sorting self and non-self, several problems might occur.
• If your immune system decides that something is foreign and dangerous, even though its not, it may result in allergies. E.g.: peanut, pollen etc.
• When the immune system attacks a normal part of the body a variety of autoimmune diseases may follow (e.g.: multiple sclerosis
• Acquired immunity:

1. Acquire the ability to target new pathogen specifically, with antibodies and cell-mediated immunity.
2. Finding which antibody has the best fit and generating many copies of it
3. Finally, repeated exposure to the new pathogen will boost the targeted defenses even more

• Innate immunity: the second any sort of pathogen hits your system, this nonspecific immune response swings into action

How does stress inhibit immune functioning?

• Stress suppresses the formation of new lymphocytes and their release into circulation, and shorten the time preexisting lymphocytes stay in the circulation
• Stress also inhibits the manufacturing of new antibodies in response to an infectious agent, and disrupt communication among lymphocytes.
• Stress inhibits the innate immune response, suppressing inflammation
• Sympathetic nervous system hormones, beta-endorphin, and CRH* within the brain play a role in suppressing immunity during stress
• Immune suppression also occurs via glucocorticoids, by causing the thymus gland to shrink

Can stress enhance the immune system?

• During the first few minutes after the onset of a stressor, your immune system is enhanced in many ways. This is seen particularly in innate immunity.
• Both physical and psychological stressors appear to cause an early stage of immune activation
• After about an hour of stress exposure, the immune system starts to get suppressed
• It is only with major stressors of longer duration, or with really major exposure to glucocorticoids, that the immune system does not just return to baseline, but plummets into a range that really does qualify as immunosuppressing
• The reason behind your immune system not being able to be constantly activated is that overactivation causes autoimmune disease, by mistaking parts of your own body as invasive

Chronic stress and disease risk

1. The individuals in question have been stressed,    
2. causing them to turn on the stress-response    
3. The duration and magnitude of the stress-response in these individuals is big enough to suppress immune function,      
4. Which increases the odds of these individuals getting some infectious disease and impairs their ability to defend themselves against that disease once they have it.

Social support and social isolation

• The fewer social relationships one has, the shorter his or her life expectancy, and the worse the impact of various infectious disease
• Could be because of the following pattern:

1. Socially isolated people are more stressed due to lack of social outlets and support
2. Stress leads to chronic activation of stress-responses
3. Leading to immune suppression
4. And finally more infectious diseases

• Infect monkeys with SIV (equivalent of HIV) and more socially isolated animals have higher glucocorticoid levels, fewer antibodies against the virus, more virus in the system and a greater mortality rate

Stress can increase the likelihood of someone getting the common cold, herpes or even developing AIDS in cases of HIV positive individuals. Overall, stress can increase the likelihood, the severity, or both of some immune-related diseases.

What does stress have to do with getting cancer?

• The rate at which some tumors grow in mice can be affected merely by what sort of cages the animals are housed in. The more noisy and stressful, the faster the tumor grows
• A number of studies show that stress increases chances of cancer in humans, but these studies are retrospective
• According to some views the cancer-prone personality is one of being conforming and compliant, repressing emotions, especially anger
• It is not in our power to cure ourselves of all our worst medical nightmares merely by reducing stress and thinking positive thoughts.

*CRH: corticotropin-releasing hormone 

Resources: Sapolsky, R. Why zebras don’t get ulcers: The acclaimed guide to stress, stress-related diseases, and coping. New York (NY): Henry Holt and Company. 2004 3rd edition