EXAM #1: HOST DEFENSE

Question 1

What is the “cytopathic effect” associated with viruses?

Answer 1

Virus induced lysis of host cells

Question 2

How does the skin prevent viral infection?

Answer 2

Keratinization prevents viral entry into the body

Question 3

How does the alimentary tract prevent viral infection? What type of virus is better suited to gain entry via the alimentary tract?

Answer 3

1) Acid and proteolytic enzymes break down viruses
2) Bile destroys ENVELOPED viruses

*Thus, naked viruses do a little better

Question 4

How does the respiratory tract prevent viral infection?

Answer 4

1) Mucus traps virus and via the mucocilliary escalator it is destroyed the stomach acid
2) Nasal turbinates impede viral entry

Question 5

What are the major components of the innate immune system that defend against viral infection?

Answer 5

1) TYPE I interferon*
2) NK Cells
3) Macrophages

*(a/B vs. gamma that is TYPE II)

Question 6

Describe the role of interferon in preventing viral infection. What is the difference between the sources of alpha and beta interferon?

Answer 6

1) Virus stimulates a/B interferon (TYPE I)
2) Interferons SURROUND infected cells
3) This inhibits viral replication/infection in ADJACENT cells

*Note that a is produced by leukocytes, B is produced by fibroblasts, BUT they both act on the same IFN receptor

Question 7

List four actions of interferon a/b.

Answer 7

1) Prevent viral replication in surrounding cells
2) Increase MHC I expression*
3) Activate dendritic cells and macrophages
4) Activate NK cells to kill virus infected cells

*Increases the CD8 T-cell response

Question 8

What is the MOA of interferon to inhibit viral replication? Draw the specific pathway.

Answer 8

1) a/B IFN binds IFN receptor
2) mRNA is degraded and eIF2 is inactivated
3) END RESULT: inhibition or protein synthesis, interrupting viral replication

Question 9

What immune cell-type is the first line of defense against virus infected cells?

Answer 9

NK cells

Question 10

Describe how NK cells are activated.

Answer 10

• Virus infected cells downregulate MHC I to prevent CTL killing
• NK cells are a back-up: they are RELEASED from INACTIVE STATE absence of MHC I proteins

*NK cell activity is also activated by IFN a/b (TYPE I)

Question 11

What is the mechanism by which NK cells kill virus infected cells?

Answer 11

ADCC–antibody dependent cell mediated cytotoxicity

• IgG/NK cell Fc receptors bind, triggering ADCC i.e. killing of the target cell

Question 12

What mediates the anti-viral effects of macrophages?

Answer 12

TNF-alpha and NO

Question 13

What is the downside of the macrophage response to viral infection?

Answer 13

Some viruses can hijack macrophages i.e. infect macrophages to facilitate viral spread

*CMV, Ebola, HIV, measles, and rubella

Question 14

When is humoral immunity most important in viral infection?

Answer 14

EARLY

Question 15

When is cell mediated immunity most important in viral infection?

Answer 15

Once infection is ESTABLISHED (CTLs)

Question 16

How do antibodies function in viral infection?

Answer 16

1) Prevent binding to target cell
2) Opsonization
3) Activate complement
4) Facilitate ADCC by NK cells
5) Downregulate expression of viral genes

Question 17

What is needed for a CTL to kill a virus infected cell?

Answer 17

Virus bound the MHC Class I

Question 18

How does the B and T cell memory response differ?

Answer 18

T cells= quiescent until reactivated

B cells= production of antibody for decades post-infection

Question 19

What are the predominate innate immunity mechanisms against intracellular bacteria?

Answer 19

1) Macrophages release IL-12; IL-12 activates NK cells
2) NK cells release IFN-g (TYPE II IFN), which further activates macrophages
- IFN-g ramps up macrophage production of NO

Question 20

What are the adaptive immune system responses to intracellular bacteria?

Answer 20

1) DTH-like reaction i.e. T-cells are activated and produce IFN-g ramping up macrophages
2) Some bacteria may persist, so the body responds by walling it off in a granuloma

Question 21

What cytokine drives Th1 mediated responses?

Answer 21

IL-12

Question 22

What cytokine drives Th2 immunity?

Answer 22

IL-4

Question 23

How can intracellular bacteria be targeted by CTLs?

Answer 23

• Bacteria escapes from phagosomes into cytosol

- Processing and expression on MHC Class I activates CLTs

Question 24

From an immunological standpoint, what is the difference between Tuberculoid and Lepromatous leprosy? Which form will show hypergammaglobulinemia?

Answer 24

Tuberculoid= Th1 mediated
Lepromatous= Th2 mediated
- Hypergammaglobulinemia

Question 25

What type of T-cell response drives granuloma formation, Th1 or Th2?

Answer 25

Th1 and IL-12 production