Introduction to B cells and antibodies Flashcards
1
Q
What are the three types of signals that antigen-presenting cells deliver to naive T cells?
A
- Activation
- Survival
- Differentiation
2
Q
Label the T cell activation types from 1-3
A
- Activation
- Survival
- Differentiation
3
Q
Label the cytotoxic T cell activation diagram from a to g
A
a - MHC-I
b - T-cell receptor
c - B7
d - CD28
e - IL-2
f - IL-2 receptor
g - Kill
4
Q
What are naive T cells?
A
T cells that have not been exposed to an antigen
5
Q
What does a naive T cell become once activated?
A
A primed T cell that proliferates and differentiates into either cytotoxic or helper T cells
6
Q
What is the affinity of resting T cells to interleukin 2?
A
Moderate
7
Q
What is the affinity of activated T cells to interleukin 2?
A
High
8
Q
What does the binding of IL-2 to IL-2 receptors on T cells promote?
A
The T cell to enter the cell cycle, proliferate and differentiate
9
Q
What are the specific antigens of the humoral immunity?
A
- IgD
- IgM
- IgG
- IgA
- IgE
10
Q
What is the role of an IgD receptor?
A
Antigen receptor for virgin B cells
11
Q
What is the role of an IgM receptor?
A
Agglutination
12
Q
What is the role of an IgG receptor?
A
Opsonisation
13
Q
What is the role of an IgA receptor?
A
Protection of mucosa
14
Q
What is the role of an IgE receptor?
A
Inflammation and protection against helminths
15
Q
What are the non-specific complementary responses of humoral immunity?
A
- Cytolysis
- Chemotaxis
- Inflammation
- Opsonisation
16
Q
What are the 4 stages of B cell activation by virus?
A
- B cell binds virus through viral coat protein.
- Virus particle is internalised and degraded.
- Viral proteins are presented to T cell which activates B cell.
- Activated B cells produce antibodies against viral coat protein.
17
Q
What are the 4 stages of B cell activation by bacterium?
A
- B cell binds bacterial polysaccharide epitope linked to bacterial toxoid.
- Antigen internalised and processed.
- Antigen epitope presented to T cell.
- Activated B cell produces antibody against polysaccharide antigen on bacterium surface.
18
Q
Where are B cells activated?
A
In lymphatic tissue where they remain
19
Q
How do B cells respond to foreign antigens?
A
- Engulf
- Fragment
- Present their epitopes on MHC-II molecules
- Differentiate into plasma cells
20
Q
What type of foreign antigens do B cells respond to?
A
Unprocessed antigens or antigen-presenting molecules
21
Q
What recognises antigen-presenting B cells?
A
T helper cells
22
Q
Label the B cell activation diagram from a to g
A
a - B cell receptor
b - B cell recognising unprocessed antigen
c - Costimulation by several interleukins
d - Proliferation and differentiation
e - Plasma
f - Memory cells
g - Antibodies
23
Q
What do T helper cells do once they recognise B cells?
A
Secrete IL-2, IL-4, IL-6 which co-stimulate B cells to differentiate into plasma cells
24
Q
What do plasma cells do?
A
Secrete antibodies that are specific to the initial stimulating antigen
25
Some B cells differentiate into plasma cells when activated, what do the others do?
Differentiate into memory B cells
26
How many polypeptide chains are there in an antibody?
4
27
What are the 4 chains of an antibody?
Two identical heavy chains and two identical light chains
28
Label the antibody diagrams from a to k
a - antigen-binding site
b - light chains
c - carbohydrate chain
d - antigen-binding site
e - heavy chains
f - stem region
g - hinge region
h - antigen-binding site
i - light chain
j - carbohydrate chain
k - heavy chain
29
How many amino acids make up the heavy chain of an antibody?
Approximately 450
30
How many amino acids make up the light chain of an antibody?
Approximately 220
31
What binds a light chain to a heavy chain in an antibody?
One disulfide bond
32
What binds two heavy chains in an antibody?
Two disulphide bonds at the mid-region forming a hinge region
33
What do both light and heavy chains posses in an antibody?
Variable regions and constant regions
34
What is the role of variable regions on antibody chains?
To confer specificity
35
Where are variable regions found on the antibody chains?
At the tips of the chains and at the apex of the antibody arms
36
How many antigen-binding sites does each antibody have?
2
37
What are hinge regions on antibodies for?
To allow the antibody the flexibility to bind to antigens in widely separated places
38
What is the constant region of an antibody?
* Neary the same in different antibodies
* Found on heavy and light chains
* Not associated with antigen binding
39
Where does the constant region of an antibody vary slightly between different classes?
On the heavy chain
40
What are the five classes of antibodies?
* IgG
* IgA
* IgM
* IgD
* IgE
41
Label the antibody isotypes diagram from a to i
a - IgG
b - IgE
c - IgD
d - IgM
e - disulphide bond
f - joining chain
g - IgA
h - joining chain
i - secretory protein
42
What does the binding of the antigen-binding site of an antibody with an antigen cause?
* Neutralisation
* Agglutination
* Precipitation
43
What is antibody neutralisation?
When an antibody covers the biologically active portion of a microbe or toxin
44
What is antibody agglutination?
When an antibodies cross-links cells to form a clump
45
What is antibody precipitation
46
What does the exposed fragment crystalisable portion of an antigen promote following antigen binding?
* Complement fixation
* Opsonisation
* Activation of NK cells
47
What is complement fixation?
Where the Fc region of an antibody binds to a complement protein; thus, activating the complement
48
What is opsonisation?
When the Fc region of an antibody binds to phagocyte receptors, promoting phagocytosis of the pathogen
49
What is the activation of NK cells?
When the Fc region of the antibody binds to an NK cell triggering the release of cytotoxic chemicals
50
What is a complement?
A system of numerous serum proteins acting in sequence that complement antibody activity in specific and non-specific immune responses
51
What is the complement immune system involved in when activated inappropriately or exaggerated?
Immunopathology
52
What are the complement proteins?
* C1, C2, C3, C4, C5, C6, C7, C8, C9
* Factor B, Factor D and Properdin
* Mannose binding protein [MBP]
53
What are the complement receptors?
CR1, CR2, CR3
54
Label the complement sequence from a to g
a - antigen
b - antibody
c - Antigen-antibody complex activates C1
d - Factor B, factor D and factor P (properdin)
e - Polysaccharides on surface of microbe
f - Membrane attacking complex
g - Microbial membrane
55
Which pathways is/are activated by microorganisms in the complement immune system?
Alternative pathway and Lectin pathway (both innate)
56
Which pathway(s) is/are activated by antigen/antibody complexes in the complement immune system?
The classical pathway - specific
57
What complement proteins are involved in the alternative pathway?
* C3
* Factor B
* Factor D
* Properdin
58
What complement proteins are involved in the lectin pathway?
* MBP
* C2
* C4
59
What complement proteins are involved in the classical pathway?
* C1
* C2
* C4
60
Describe the 15 steps of the classical pathway
1. IgM/IgG antibody binds to antigen epitopes.
2. C1 binds to the Fc region of antibodies.
3. C1r activates C1s which is a proteinase.
4. C1s cleaves C4.
5. C4b binds to antigen; C4a remains in fluid phase.
6. C1s cleaves C2.
7. C2b binds to antigen; C2a remains in fluid phase.
8. C2b is a proteinase that cleaves C3.
9. C3b binds to antigen; C3a remains in fluid phase.
10. C2b cleaves C5.
11. C5b doesn't spontaneously bind; C5a in fluid phase.
12. C5b binds C6, C7 and C8 in fluid phase.
13. C5b678 binds to the lipid-bilayer.
14. C9 inserts a hole into the membrane.
15. Microorganism is lysed by the membrane attack complex.
61
What is the reaction caused by the membrane attack complex described as?
An enzymatic cascade
62
What does the membrane attack complex do?
* Form pores in membranes of microorganisms.
* Kills gram-negative bacteria, enveloped viruses and some protozoan parasites.
63
How do gram-positive bacteria protect themselves against complement protein-mediated lysis?
Thick peptidoglycan cell walls
64
How do fungi protect themselves against complement protein-mediated lysis?
Thick chitin cell walls
65
Where does the classical pathway stop when attacking gram-positive bacteria
C5 cleavage
66
What effect does complement protein-mediated lysis have on gram-positive bacteria?
* Doesn't directly kill them.
* Plays an important part in their elimination from the body by other biological effects.
67
What other biological effects from complement protein-mediated lysis aid the elimination of gram-positive bacteria from the body?
The biological activities of complement cleavage products C3a, C5a and C3b
68
What type of complement cleavage products are C3a and C5a?
* Anaphylatoxins that activate mast cells.
* Chemotaxins that attract phagocytes (neutrophils and mononuclear phagocytes).
69
What type of complement cleavage product is C3b?
An opsonin that enables phagocytes to recognise and bind to antigens and phagocytose them.
70
What type of immunity is the alternative pathway found in?
The innate immunity
71
What does the innate immunity not involve?
Antibodies
72
In the alternative pathway, what do Factors B and D and Properdin interact with?
Microbial surface polysaccharides
73
What biological activity is activated by the alternative pathway?
* Membrane attack complex
* C3a and C5a
* Opsonisation by C3b
74
What is a xenograft?
A tissue graft or organ transplant from a donor of a different species from the recipient.
75
What occurs when the immune system recognises a xenograft?
Hyperacute rejection
76
What mediates hyperacute rejection?
Naturally occurring antibodies to 𝝰-Gal.
77
What are the naturally occurring antibodies to 𝝰-Gal?
* Gala1
* 3Galb1
* 4GlcNAc
78
Where is 𝝰-Gal found?
As a residue on cell surface glycoproteins and glycolipids on animal cells.
79
What enzyme is used to synthesize 𝝰-Gal?
a1, 3Galactosyl transferase
80
What animal species lack a1,3Galactosyl transferase?
Humans, apes and old world monkeys - lost during evolution.
81
Why do humans recognise 𝝰-Gal as foreign?
Humans do not express 𝝰-Gal epitopes.
82
Humans have [high/low] titres of antibodies to the 𝝰-Gal epitope.
high
83
What is believed to induce cross high titres of 𝝰-Gal antibodies in humans?
Cross-reactive microbial antigens in the gut
84
Which 4 steps occur when an organ graft that is hyperacutely rejected?
1. Antibodies enter donor blood vessels and bind to 𝝰-Gal epitopes on endothelial cells.
2. Complement is activated and neutrophils are attracted to the site destroying the endothelial cells.
3. Thrombus formation blocks the vessels.
4. The organ dies of oxygen deprivation within hours.
85
Define xenogeneic
An adjective that describes a tissue as belonging to a different species.
86
What are the two pathways for acute immune rejection of xenogeneic tissues?
* Direct - incompatible MHC-II on animal cells.
* Indirect - incompatible MHC-I on animal cells.
87
Define immunogenic
Able to activate an immune response
88
What are immunogenic components of the extracellular matric of different animal species?
* Collagen and elastin
* Glycosaminoglycans
89
Define immunological memory
The ability of the immune system to quickly and specifically recognize an antigen that the body has previously encountered and initiate a corresponding immune response.
90
What remains after an immune response?
Memory T and B cells.
91
What can memory T and B cells do if they re-encounter the same antigen again?
Quickly proliferate.
92
What is used to measure immunological memory?
The antibody tire
93
How does the antibody titre change when exposed to a new antigen?
Increases after contact and then steadily decreases after the immune response.
94
What is the initial contact with an antigen called?
The primary response
95
What is the secondary response?
When an antigen is encountered a second time and the memory cells become activated.
96
What happens in the secondary response?
Memory cells quickly proliferate and produce vast quantities of mostly IgG antibodies.
97
What forms the basis of vaccination?
Immunological memory
98
What is the correlation between old age and immune function?
Negative: as old age increases, immune function decreases.
99
What happens to the function of T cells in old age?
They become less responsive to antigens
100
Why do T cells become less responsive in old age?
Atrophy of the thymus and a decrease in thymic hormones
101
What is associated with the decrease in T cells in old age?
Decrease in B cells
102
How often are influenza vaccinations provided for the elderly?
Every year
103
Why are influenza vaccines given to the elderly so often?
Because they take longer to increase their antibody titre because of their decreased levels of B and T cells.
