3 - Innate and Acquired Immune System

Question 1

Functions of innate system

Answer 1

1. Initial defence against microbes
2. Eliminates damaged cells + initiates repair
3. Stimulates adaptive immune response

Question 2

Describe the chemical defence of the innate system

Answer 2

antibacterial peptides

• Small amino acids cationic with anti-microbial activity
• Defensins: kill a wide range of bacteria within minutes
• Secreted by neutrophils, disrupting membranes to form pores resulting in lysis

Question 3

Describe the purpose of inflammation response by innate immunity

Answer 3

• Triggered by cellular injury
• Attempts to prevent spread of agent
• Dispose debris and pathogens
• Tissue repair

Question 4

What are the signs of inflammation?

Answer 4

Redness, heat, swelling, pain + loss of function

Question 5

Describe the pathway of an inflammatory response

Answer 5

injury
release of inflammatory mediators
acute inflammation: removal of damaging stimulus
cells regenerate or heal by scar formation

Question 6

Provide examples of inflammatory mediators

Answer 6

1. Cytokines
   - Proteins released by cells that affect other cells
2. Chemokines
   - Proteins released by cells that attract other cells to the area
3. Acute-phase proteins
   - Plasma proteins that increase in concentration due to inflammation within minutes

Question 7

Describe phagocytosis

Answer 7

Microbes and killed and removed

• Phagocytic cell recognises surface of microbe -> adheres -> ingests
• Held within phagosome, fusing with a lysosome to form phagolysosome
• Exocytosis removes microbe debris

Question 8

What are the toxic substances that kill and degrade mircobes in phagocytosis?

Answer 8

• Nitric oxide
• Superoxide anions
• Hydrogen peroxide

Question 9

Describe NK cells

Answer 9

• Eliminates virally infected and cancer cells
• Recognises reduced MHC class I via activating + inhibitory receptors
• Direct cytotoxicity by release of perforin + granzymes

Question 10

What does ADCC stand for?

Answer 10

Antibody dependent cell mediated cytotoxicity

Question 11

What is ADCC?

Answer 11

NK cells are able to attach to antibodies on surface of cells via Fc receptor

Question 12

Describe the missing self hypothesis

Answer 12

• When inhibitory receptor is engaged, the NK cell is not activated -> no cell killing
• When the inhibitory receptor is not engaged, the NK cell is activated -> infected cell is killed

Question 13

What are the two ways the innate system is stimulated?

Answer 13

PAMPs - Pathogen associated molecular patterns

DAMPs - Damage associated molecular patterns

Question 14

How does PAMPs work to stimulate the innate system?

Answer 14

Different structures on different pathogens are recognised by cells of the innate system

Question 15

How does DAMPs work to stimulate the innate system?

Answer 15

Molecules released from damaged cells

• endogenous
• released in response to trauma
• healthy cells are able to release alarmins in response to infection to enhance innate response

Question 16

What are the receptors of the innate system?

Answer 16

Pattern recognition receptors: cellular phagocytes and soluble molecules

Question 17

How do cellular phagocytes work as receptors?

Answer 17

Bind to PAMPs/DAMPs to activate signal transduction pathway

promoting inflammation + antimicrobial activity

Question 18

How do soluble molecules work as receptors ?

Answer 18

Enhances phagocytosis
Active extracellular killing
found in the blood and ecf

Question 19

Give an example of a cellular PRR

Answer 19

Toll like receptors (TLR)

Question 20

Where are toll like receptors found?

Answer 20

TLR 1,2,4,5,6,10,11 found on plasma membrane

TLR 3,7,8,9 found on endosome -> viral infections

Question 21

Give an example of soluble PRR

Answer 21

Pentraxins
Found on plasma
e.g. c-reactive protein

Question 22

Describe NOD like receptors

Answer 22

Specific for intracellular pathogens
In cytosol
Activated by peptidoglycan, RNA, toxins, flagellin
releases pro-inflammatory cytokines

Question 23

What are interferons?

Answer 23

inflammatory mediators

broad spectrum antiviral agents

Question 24

What are the interferon groups?

Answer 24

IFNA: for viral infection
IFNb: for viral infection
IFNy: for inflammatory

Question 25

How do interferons work?

Answer 25

Bind to specific receptors of neighbouring cells

• neighbouring cells produce protein kinase R
• limiting spread of viral infections to stop production of protein in a cell
• stimulates endonuclease production which degrades viral mRNA

Question 26

Describe antigen presenting cells

Answer 26

• cells that phagocytise infectious invader
• migrate to lymph node
• digest + present bits of antigen to T-helper cells
• types: dendritic cells + macrophages

Question 27

Describe humoral immunity

Answer 27

• Antibody mediated
• Acts against extracellular invaders
• Produced by B lymphocytes

Question 28

What is the action of antibodies in humoral immunity?

Answer 28

• Activate complement
• Trigger phagocytosis
• Neutralise viruses + toxins
• Aggulutination

Question 29

Describe cell mediated immunity

Answer 29

• Lymphocytes directly/indirectly kill infected cells
• Act against intracellular invaders (viruses + mycobacteria)
• Cytotoxic T cells

Question 30

What are the classes of antibodies?

Answer 30

IgG, IgA, IgM, IgE, IgD

Question 31

Primary response

Answer 31

Lag of several days as B cells proliferate
aby levels peak + fall as ag is removed
Aby is predominantly IgM

Question 32

Secondary response

Answer 32

Second exposure to same antigen
Quicker + larger response
Rapid rise in aby levels + lasts longer 
Memory cells have fewer cycles to become plasma cells 
Aby is predom. IgG

Question 33

Describe clonal selection

Answer 33

Ag only binds to specific aby

• specific antigen binds to region of b-cell surface aby
• b cell is stimulated
• clone is selected

Question 34

Describe cytotoxic T cells

Answer 34

• require T-helper cells
• wide range of surface receptors against ag
• each Tc is specific for one receptor
• infected cell express ag on their surface via MHC I
• Tc via T-cell receptor binds + destorys cells expressed the specific ag
• kill by release of toxins -> lysis -> initiate apoptosis