Chapter 9

Question 1

Infection

Answer 1

presence or growth of a pathogen in the body

Question 2

Viral infection

Answer 2

presence or growth of a pathogenic virus in the body
Theoretically, require one virion
Practically, require minimum infectious dose

Question 3

Acute infection

Answer 3

Rapid onset, lasts for a short time

Question 4

Persistent infection

Answer 4

lasts for a long time

Question 5

Cytocidal infection

Answer 5

Cell death

Question 6

To establish infection, a virus must

Answer 6

1. Gain access to a permissive cell

2. Overcome host defense

Question 7

Permissive cells

Answer 7

Have receptors for virus to bind
Have all requirements for viral replication
Permit viral replication inside

Question 8

Interferon

Answer 8

protein produced by cell in response to viral infection

• α-, β-, and γ-

Question 9

α-, β- interferon

Answer 9

produced by virus infected cell to protect nearby cells

bind to interferon receptor -> trigger anti-viral activity

Question 10

γ- interferon

Answer 10

produced by T and NK cells to activate T cell-mediated immunity
Stimulate antigen-presenting, phagocytes, NK cells

Question 11

NK cell

Answer 11

present throughout body, but mainly in blood
• recognize surface change of virus-infected cells
• Bind and kill them by releasing perforin or inducing apoptosis
• Release γ-interferon

Question 12

Perforin

Answer 12

A pore-forming protein
Produced by killer cells of immune system
-> a channel in cell membrane of target cell-> cell death

Question 13

APOBEC3 proteins

Answer 13

enzymes induce lethal mutation: dC->dU during reverse transcription -> interfere with replication of retroviruses

Question 14

Lymphocytes

Answer 14

Key cell in specific(adaptive) immunity

B-cells and T-cells

Question 15

B- cells

Answer 15

develope in bone marrow -> antibody-mediated immunity

Question 16

T-cells

Answer 16

matured in thymus -> cell mediated immunity
Helper T cells (TH, CD4)
Cytotoxic T Cells (TC, CD8)

Question 17

Antibodies

Answer 17

• Glycoproteins contain antigen binding sites
• Ig (immunoglobulins) IgG, IgM, IgA, IgE, IgD
• Produced by plasma cells derived from B cell
• Bind specific Ag on virion on infected cells

Question 18

Outcomes of antibody binding to virus antigen

Answer 18

• Neutralization: block virus -> lose infectivity
• Increase phagocytosis: Fc region binds Fc receptor on phagocyte -> destroy virus
• Active complement -> cell lysis

Question 19

Helper T cells

Answer 19

(TH, CD4)

Stimulate other immune cells by secreting cytokines

Question 20

Cytotoxic T cells

Answer 20

(TC, CD8): “killer T cell”

Kill infected cells by releasing perforin or by inducing apoptosis

Question 21

How T cell recognizes cell

Answer 21

Te cell receptor recognizes Antigen presented Major Histocompatability Complex class I of infect cell

Question 22

RNA silencing

Answer 22

Post transcriptional gene silencing or RNA interference
• Induced by dsRNA
• Destroy sequence specific mRNA (a part of its sequence is the same as a part of inducing ds RNA)
• Dicer: cellular enzyme cleaves dsRNA
• siRNA: small interfering dsRNA (21-25 bp)
• RNA-induced silencing complex
• Activated RISC
o (+) RNA fragment is removed
o (-) RNA bind to mRNA w/ complement sequence
• mRNA cleaved in that region by RISC protein

Question 23

Apoptosis

Answer 23

Programmed cell death in animal cell
A series of genetically programmed events leading to cell death
Bacteria have similar mechanism to protect bacterial population

Question 24

Outcomes of virus-infected cell

Answer 24

Productive infection

Non-productive infection( no progeny virions produced)

Question 25

Productive infection

Answer 25

Produce progeny virus Cell death or persistent infection: long term

Question 26

Latent infection

Answer 26

``` persistent but not productive Viral genome maintained in infected cell Integrate into cell genome Or persist as multiple copies of circular genomes may be activated by induction ```

Question 27

Abortive infection

Answer 27

Incomplete virus replication | Genome not persisted in infected cell

Question 28

Causes of abortive infection

Answer 28

Non-permissive cell Defective virus Host defense Abortive infection may also kill host cell

Question 29

Disease

Answer 29

abnormal state of the body resulted from infection, chemical, physical or genetic effects

Question 30

Symptom

Answer 30

subjective change in the body, felt by a patient as a result of disease

Question 31

Sign

Answer 31

objective changes, observable detectable

Question 32

Incubation Period

Answer 32

time between viral entry and appearance of syptoms

Question 33

Viremia

Answer 33

virus present in bloodstream

Question 34

Subclinical Infection

Answer 34

asymptomatic

Question 35

Carrier

Answer 35

infected but asymptomatic

Question 36

Disease in animal/humans

Answer 36

Infection may not cause disease Not all viruses are pathogens Some viruses are pathogenic only under certain conditions

Question 37

8 Stages in Viral Pathogenesis (animal/human)

Answer 37

1. Entry into host cell 2. Primary virus multiplication 3. Spread through host 4. Host immune responses 5. Secondary viral multiplication 6. Cell/tissue injury 7. Transmission 8. Resolution, persistence, or death

Question 38

Cell or tissue tropism

Answer 38

the tendency of a virus to favor replication in a specific type of cells or tissues

Question 39

Fates of virus-infected host

Answer 39

Fate is determined by virus factors, host factors, and environment Recovery Persistent Infection Death(cytocidal infection)

Question 40

Recovery

Answer 40

clearance of virus; or become carrier

Question 41

Persistent Infection

Answer 41

Chronic: virus always detectable Latent: dormant, but viral genome is in host cell Slow: very long incubation period