Defenses and Pathogens

Question 1

What are the different defense strategies?

Answer 1

1. Avoidance:
   
   • innate and learned aversion to signals associated with microbial
     density
   • social immunity
2. Resistance:
   
   • immune system: detection & elimination of pathogens
   • Arms race + immunopathology
3. Tolerance:
   
   • No direct effect on pathogens, but tissue protection and repair
   • Less arms race

Question 2

What is innate immune system? What is adaptive immune system? What are the differences between them?

Answer 2

Innate immune system:
- Found in all animal species
- Rapid and more general response
1. skin and mucosal epithelial
2. phagocytes
3. complement system
4. type I interferons
5. natural killer cells
Adaptive immune system
- Unique to vertebrate species
- Slower to respond, but provides memory, flexibility and precision
- Recognizing “self” from “non-self”
- Memory & anticipatory function

Question 3

Why are pathogens so harmful to us?

Answer 3

1. Hiding inside the host
   - Mycobacterium leprae turn nerve cells into stem cells and invade muscle tissue
   - Plasmodium hides in red blood cells
2. Disguising
   - Trypanosomes (sleeping sickness, Chagas, Leishmaniasis have variable surface glycoproteins
3. Suppression of the immune system
   - Herpes family viruses block presentation of MHC class I molecules that signal viral presence

Question 4

Why does antibiotic resistance evolve so quickly? Which strategies could be applied to prevent it?

Answer 4

1. Degradation of antibiotics
2. Change target proteins
3. Change membrane permeability
4. Horizontal gene transfer

Strategies to prevent it:

1. Lower doses & shorter treatments
2. Application of multiple types of antibiotics
3. Phage therapy

Question 5

What is cancer?

Answer 5

Cancer is excessive, uncontrolled growth in tissues:

1. benign
2. malignant

Question 6

Why animals have cancer?

Answer 6

1. The evolution of ageing
   
   • Reproduction versus somatic maintenance trade-off
   • Demographic transition in human populations
2. Body size
   
   • Larger animals (= more somatic cells) have a higher chance of cancer
3. Stem cells
   
   • Development & tissue repair
   • Potential to proliferate and differentiate anywhere in tissues
   • Controlled by tumor-suppressor gene p53

Question 7

Why humans have a high incidence of cancer?

Answer 7

1. Long post-reproductive lifespan
   
   • Reduced selection on diseases that occur after reproduction is finished
   • “Protected” lifestyle
2. Mismatch and cultural risk factors
   
   • Tobacco, alcohol, high-fat and high-calorie diets, pollution
3. Reproductive cancers as by-products of our unique sexuality
   
   • Continuous ovulation: risk of mutation at cell division and proliferation
   • Correlation of lifetime ovulatory cycles and risk of ovarian cancer
   • Historically: ~100 ovulatory cycle per lifetime on average, now 300-500
4. Highly invasive placenta