L18: Infection and Immunity

Question 1

List the key events during Infection

Answer 1

1. reservoir for organims
2. transmission to person
3. adhesion to site of infection
4. overcome barriers to establishing infection
5. spread to other sites
6. avoid host defences
7. disease due to microbe or host response
8. death or immunity

Question 2

what two facotrs influence the outcome of an infection?

Answer 2

microbial and host factors

Question 3

What are microbial factors that influence infection

Answer 3

1. type of organism
2. dose (degree of exposure)
3. virulence
4. route of entry

Question 4

What are host factors that influence the outcome of infection?

Answer 4

1. integrity of innate barriers
2. competence of adaptive immune system
3. genetic capacity to respond to particular organism

Question 5

what are the 4 ways of protecting against pathogen?

Answer 5

1. anatomic barriers
2. complement/antimicorbial proteins
3. innate immune cells
4. adaptive immunity

Question 6

Explain how the innate immune response works

Answer 6

• Innate immune cells express receptors (TLR) that detect molecular components common to many bacteria or ciruses eg. LPS (gram -ve)
• “sensor cells” secrete cytokines (inflammatory mediators) –> signal to other immune cells

Question 7

Humoral vs cell mediated immunity –> adaptive immunity

Answer 7

• depends on antigen specific immune cells
• antigen specificity possible via highly variable **antigen receptors **

Question 8

Th1

Answer 8

• cytotoxic response
• inflammation
• viral infections and ingested/intracellular bacteria

Question 9

Th2

Answer 9

• IgE - allergy reposen
• immunity against extracellular pathogens (eg worms)

Question 10

What is the mechanism for immunity to bacteria

Answer 10

AB and complement work together

Question 11

what are the benefits of AB and complement working together?

Answer 11

1. enhance bacterial destrcution
2. enhance phagocytosis (opsonisation)

Question 12

What are the three ways to activate complement

Answer 12

1. lectin
2. classical
3. alternative

Question 13

What is a common feature to all three pathways

Answer 13

1. all pathways generate a C3 convertase, cleaves C3 to C3b and C3a
   - activates complement
2. lead to effector activities

Question 14

C3b

Answer 14

bound to microbial surface

Question 15

What are the three effector functions of complement activation?

Answer 15

1. recruitment of inflammatory cells - promote inflammation
2. opsonisation of pathogens - binding of C3 triggers phagocytosis
3. killing of pathogens - MAC complex

Question 16

mechanisms of bacterial resistance

Answer 16

1. caspule - charge, phyically repel
2. Intracellular growth

Question 17

what is the innate mechanism of the antiviral response?

Answer 17

interferons and NK cells

Question 18

what is the adaptive mechanism of the antiviral response?

Answer 18

antibody neutralization, CD8+ T-cells

Question 19

explain how the interferon response works on neighbouring cells

Answer 19

1. Infected cells turn on interferon response
2. neighbouring cells receive signal
3. viral resistance of these cells
   –> transient virus resistance

Question 20

explain how the interferon response works on NK cells

Answer 20

1. interferon signalt to NK cells
2. amps up NK cell production
3. killd neighbouring infected cells

Question 21

Explain the dynamics of the IFN response

Answer 21

early response: keeps viral load low, mild disease
late/delayed: viral persistence, high viral load (supress response), exaggerated IFN response later - cause severe disease