Immunology

Question 1

Do lymphatic vessels have valves?

Answer 1

Yes.

They prevent reverse flow.

Question 2

What is the main role of the lymphoid system?

Answer 2

React decisively and precisely against foreign invasion.

Question 3

What are some forms of innate immunity?

Answer 3

Epithelial barriers
Neutrophils
Macrophages
Complement

Question 4

What are some forms of adaptive immunity?

Answer 4

T and B cells.

Acquired antigen specific immunity and humoral and cell mediated immunity.

Question 5

Through what mechanisms is innate immunity enforced?

Answer 5

Body temperature - higher temperatures decrease viability of invading pathogens.
Skin and mucosal membranes - mucous, motility of gut and cilia and normal bacteria flora.
Antimicrobial substances in blood and body fluids - protective serum proteins, lysozyme, complement, interferon, commensals.
Phagocytic cells ( neutrophils, macrophages, NKC).

Question 6

What are some examples of antimicrobial peptides in vertebrates?

Answer 6

Peptides with hydrophobic motifs that disrupt bacterial cell walls.
Cathelicidins - epithelial cells, macrophages, neutrophils.
Defensins
Cecropins - insects
Crotamine - rattlesnake venom

Question 7

What are commensals and what is their role?

Answer 7

Role in innate immunity.

Bacteria that live on host but neither has much effect on each other - competition for invading bad bacteria.

Question 8

What are some actions that the body carriers out that are associated with innate immunity?

Answer 8

Vomiting
Coughing
Saliva
Sneezing
Blinking
Tears
Diarrhoea

Question 9

What is complement?

Answer 9

Series of plasma proteins (made in liver) that get activated in a triggered enzyme cascade.
Major defence system of the body.

Question 10

What are the 3 ways of activating the complement cascade?

Answer 10

Classical pathway
Alternative pathway
Lectin pathway

Question 11

What occurs during the classical pathway of the complement cascade?

Answer 11

1) C1 binds Ab:Ag causing conformational change.
2) C1r is activated, C1s is activated.
3) C4 cleaved into a and b.
4) C4b cleaves C2 into a and b.
5) C4b binds C2a
6) C4b2a cleaves C3 into a and b.

Question 12

How is the classical pathway regulated?

Answer 12

C1 inhibitor (binds C1r and C1s).
Block of C4b2a (C3 convertase).
Control proteins block complement binding to cell surface.

Question 13

What occurs during the alternative pathway?

Answer 13

Spontaneous - doesn’t require antibody (IgA).
C3b binds to hydroxyl and amine groups on micro-organisms cell surface.
Part of innate immunity.

Question 14

How is the alternative pathway regulated?

Answer 14

Positive feedback inhibition

Control proteins

Question 15

What occurs during the lectin pathway?

Answer 15

Mannan binding lectin (MBL) binds to mannose groups.

Activates 2 proenzyme serine proteases (homologous to C1r and C1s).

Question 16

What is MBL?

Answer 16

Mannin binding lectin (collagen like lectin) that binds to yeasts, bacteria, viruses and parasites to initiate the complement cascade.

Question 17

What are lectins?

Answer 17

Proteins that bind sugar.

Question 18

What are collectins?

Answer 18

Collectins can aggregate pathogens, neutralise viruses, attract and activate phagocytosis.
Key role in host defence.

Question 19

What is the end result of the complement cascade?

Answer 19

Production of a membrane attack complex that binds to pathogens membrane.

Question 20

Which 2 pathways generate C3 convertase? What does it do?

Answer 20

Converts C3 to C3b - C3b then activates the terminal sequence leading to production of the membrane attack complex.
Occurs in classical pathway in response to antigen/antibody complexes.
Occurs in alternative pathway (innate) in response to micro-organisms.

Question 21

What are the 3 proteins that affect C3b?

Answer 21

C1 inhibitor - inactivates C1.
Protein H - inhibits binding of factor B to membrane bound C3b.
Factor I - cleaves membrane bound C3b into c and d (inactive). Occurs mostly on RBC’s.

Question 22

What are the 3 effector mechanisms? What does complement enhance?

Answer 22

Opsonisation
Chemotaxis
Lysis

Question 23

What is opsonisation?

Answer 23

Coating of microorganism with complement proteins, C3b.
Leads to binding of phagocytic cells via complements receptors and enhanced phagocytosis.
Requires a complement receptor.

Question 24

What is chemotaxis?

Answer 24

Attraction of polymorphs to sites of inflammation via complement receptors.

Question 25

How does lysis occur?

Answer 25

Via MAC formation of lytic pore.

Question 26

List some complement receptors.

Answer 26

CR1
CR2
CR3
CR4

Question 27

How can pathogenic bacteria evade complement?

Answer 27

Bacterial capsule that resists opsonisation

Question 28

How can viruses evade complement?

Answer 28

CR2 is Epstein Barr Virus entry receptor.

CR3 is West Nile Virus entry receptor.

Question 29

How can yeast evade complement?

Answer 29

Express CR2 and 3 molecules.

Regulate C cascade.

Question 30

How can Trypanosomes evade complement?

Answer 30

Molecules inhibit complement activation.

Question 31

What diseases can occur if your complement system is overactive?

Answer 31

Immune complexes deposited on surfaces - bacterial endocarditis, glomerulonephritis.
Anaphylaxis - bacterial sepsis, cardiovascular collapse.

Question 32

What can occur if their are deficiencies in the complement components?

Answer 32

Lack of C3 - overwhelming bacterial infections

Lack of C8 - Neisserial infections

Question 33

What 4 features are involved in innate resistance to microbial invasion?

Answer 33

Anatomical
Physiological
Chemical
Enzymatic