Sickness Behaviours

Question 1

vaccines

Answer 1

• Inactive virus (due to heat, chemicals, radiation) - can’t replicate
• Live attenuated vaccine: unable to activate, attenuated through passage into foreign host

Question 2

herd immunity

Answer 2

indirect protection from an infectious disease; occurs when a large percentage of the population is immune to infection (ie. Through flu shots)

Question 3

primary line of defense

Answer 3

barriers that keep foreign material out (ex. Skin, saliva, mucus & cilia, stomach acid); innate immunity

Question 4

secondary life of defense

Answer 4

mechanisms targeting foreign material that enters the body – in the bloodstream (ex. White blood cells, cytokines); innate & adaptive immunity

Question 5

cytokines

Answer 5

hormones of immune system

Question 6

immune system

Answer 6

composed of organs and tissues, including primary lymphatic organs and secondary lymphatic organs

Question 7

primary lymphatic organs

Answer 7

• where lymphocytes are formed and mature
• • Bone marrow
• • Thymus

Question 8

secondary lymphatic organs

Answer 8

• series of filters that sample and monitor the contents of the extracellular fluids (lymph, tissue fluid, blood)
• • Lymph nodes
• • Spleen
• • Tonsils
• • Mucosa associated lymphoid tissue (MALT)

Question 9

functions of immune system

Answer 9

• Protection from pathogens
• Critical role in brain development (cytokines are critical mediator of functions related to brain maturation)
• Impacts behaviour

Question 10

link between immune system and social behaviour (mice study)

Answer 10

• normal mice and mice lacking functional immune system given social preference task (novel objects vs. novel mouse)
• Normal immune system: mice prefer other mouse
• Lack of immune system: no preference
• Repopulated immune system: now prefer other mice
• cytokine IFN-Gamma required for normal social behaviour

Question 11

cytokine IFN-Gamma

Answer 11

• required for normal social behaviour in mice
• inhibits neurons in the prefrontal cortex – required for normal social behaviour
• Without IFN-gamma, the PFC is overactive and the mouse is asocial

Question 12

Why does immune system impact social behaviour?

Answer 12

• evolved alongside it (with social behaviour/close contact, disease spreads quickly)
• rhesus monkey study showed that monkeys housed in social isolation had higher cytokine levels -> correlation with depressive symptoms

Question 13

Major histocompatibility complex (MHC)

Answer 13

• surface proteins expressed on cells – tells your immune system which cells are “on your team” vs. “intruders” that need to be attacked
• Wide variation within population
• Co-dominantly expressed: express both maternal and paternal copies
• Ex. If you receive an organ transplant, your body would mount an immune response and reject it unless it was from an MHC match
• during cell turnover, microbes break down MHC fragments, resulting in odor -> this odor results in attraction to potential mates (we can sense of similar someone is to us genetically based on odor)

Question 14

immune system and mate selection experiment

Answer 14

• 90 married couples; 152 randomly-generated control “couples”
• Married couples had more MHC dissimilarities than the control couples
• MHC protein playing role in mate selection
• • MHC dissimilarities: implies genetic differences; decreased risk or disorders
• • Evolutionary strategy for avoiding incest

Question 15

sickness behaviour

Answer 15

• an adaptive response to illness, often precipitated by infection
• as a result, energy is shifted to wound healing

Question 16

symptoms of sickness behaviour

Answer 16

• Social withdrawal
• Decreased appetite
• Lethargy
• Impaired concentration
• Depressed mood
• Irritability
• Muscle aches, pain, fever

Question 17

why are sickness behaviours important (other than curing infection)?

Answer 17

• Recognizing illness

- Promoting patterns likely to reduce the risk of being infected

Question 18

immune system and psychological stressors

Answer 18

• psychological stressors can activate immune system

- from evolutionary perspective, stress was often felt prior to being wounded, so over time these things were linked

Question 19

sickness behaviours vs. depression

Answer 19

• huge overlap in sickness behaviours and depressive behaviours
• social withdrawal, decreased appetite, lethargy, impaired concentration, decreased mood, irritability

Question 20

Pathos Host Defence (PATHOS-D) Hypothesis

Answer 20

• why wouldn’t natural selection have eliminated depression? (it doesn’t produce fitness advantages)
• Theory: Alleles for depression and immunological alleles that support pathogen defense are one in the same
• Over evolutionary time, the survival benefits of enhanced inflammatory activity, characteristic of depression, outweighed associated costs