Chapter 8: Immunity, Stress and Disease
I. Brain has a “vast potential for sticking its nose into the immune system’s business.”
A. Actors have increased or decreased immune responses when doing euphoric vs. depressing scenes.
II. Immune system basics: see Immunity handout
III. How does stress inhibit immune function?
A. Selye: Glucocorticoids shrink thymus gland.
1. Inhibit release of interleukins & interferons; thus, lymphocytes are less responsive to invaders.
2. They also return circulating lymphocytes to storage sites and even kill lymphocytes (“dead as a doorknob”) by causing them to produce a suicide protein.
B. Symp. N.S. hormones, beta-endorphin, and CRF in the brain also contribute in unknown ways.
IV. Why is immunity suppressed during stress?
A. Prolonged, severe stress causes energy expenditure to disassemble immune system cells and tissues.
B. With shorter duration stressors, there is actually an increase in immune responses for about 30 min. Then responsiveness returns to normal. Only severe, prolonged stressors really inhibit immunity.
C. The downturn after the initial rise is due to “sculpting” by glucocorticoids—removing older, less functional lymphocytes.
D. Also, some of the lymphocytes that leave circulation are just sent to the front lines—not to mothballs.
E. Prolonged overstimulation of the immune system à autoimmune diseases.
1. Large doses of glucocorticoids are sometimes used to treat autoimmune disorders.
2. However, stress often worsens these disorders—probably because of repetition of the early increasing phases of the response.
V. Chronic stress and disease risk
A. Why isn’t the link stronger?
1. Variable severity of stressors & perception of stressfulness. (Problem with retrospective studies.)
2. Moderate increases in glucocorticoids actually stimulate the immune system.
3. Minor immune fluctuations may not be too critical.
4. Scientists don’t deliberately make us sick, like they do lab animals.
5. If there is an apparent connection, it may be due to lifestyle or risk factors.
B. Social isolation and longevity
1. Social relationships: as important a factor as smoking, hypertension, obesity, & inactivity.
2. Not just due to altered risk factors: Same effect in monkeys in controlled conditions.
1. May hasten death only if there is an additional stressor or loss of another loved one.
2. AIDS: those who lost a loved one had worse immune decrease.
D. The common cold
1. People rated how stressed they felt, then were exposed to rhinovirus: more stressàmore colds.
2. Same finding in monkeys.
1. Rats: controllable stressàno effect; uncontrollable stressàmore virus-caused cancers. But most human cancers are caused by genetic and environmental factors.
2. Rats: glucocorticoids decrease the number of natural killer cells, increase angiogenesis, and increase blood glucose.
3. Humans: problems with retrospective studies. Little link with cancer onset.
4. Optimism, assertiveness, and social support can extend life in those who already have cancer. This may be due to greater likelihood of taking medicine, etc.
F. Cancer and miracles (Bernie Siegel): They don’t work!
G. Postscript: A grotesque piece of medical history:
1. SIDS kids had larger thymus glands than “normal” children. Therefore, doctors started irradiating the thymus to shrink it; à thyroid cancers!
2. However, the “normal” children had died of chronic malnutrition, or prolonged stressful diseases.