Adaptive immunity 2 (B cells)

Question 1

Which subset of T cells drive antibody production by B cells?

Answer 1

TH2 CD4+ T cells

Question 2

Where do B cells originate and mature?

Answer 2

Bone marrow (from haemopoetic stem cells)

Question 3

Where are B cells found in large populations?

Answer 3

lymph, lymph nodes, spleen, specialised lymphoid tissues (secondary lymphoid organs)

Question 4

Which branch of the adaptive immune system is driven by B cells?

Answer 4

Humoral immunity (produce antibodies)

Question 5

Function of B cells

Answer 5

produce antibodies, and are capable of antigen presentation for T cell activation

Question 6

What are the 2 main subsets of B cells?

Answer 6

plasma cells and memory B cells

Question 7

How many types of antibodies exist?

Answer 7

5

Question 8

Which professional immune cells are capable of antigen presentation?

Answer 8

dendritic cells, macrophages, B cells

Question 9

How do B cells recognise antigens?

Answer 9

via the B cell receptor (BCR) which has extreme diversity

Question 10

What is the B cell receptor essentially?

Answer 10

an antibody (2 of the 5 antibody types are BCRs)

Question 11

Which of the 2 antibody types form BCRs?

Answer 11

IgM or IgD

Question 12

When does BCR diversity arise?

Answer 12

during B cell education in the bone marrow

Question 13

Where are B cells activated?

Answer 13

In the periphery in secondary lymphoid organs (lymph nodes, spleen, specialised lymphoid tissues)

Question 14

What happens once B cells are activated?

Answer 14

differentiate into plasma cells and memory B cells

Question 15

Function of plasma cells

Answer 15

produce antibodies

Question 16

function of memory B cells

Answer 16

produce a faster antibody response during a reinfection

Question 17

Where does B cell education occur?

Answer 17

In the bone marrow

Question 18

What happens during B cell education?

Answer 18

VDJ recombination and negative selection

Question 19

What process creates diversity in the BCR?

Answer 19

VDJ recombination

Question 20

Which region of the BCR is affected by VDJ recombination?

Answer 20

variable region (antigen binding site) - constant region remains the same.

Question 21

Why do B cells not need to undergo positive selection?

Answer 21

B cells do not need to interact with MHC receptors on host cells (unlike T cells)

Question 22

Which gene segments code for the light chain of BCRs?

Answer 22

V (variable) and J (joining)

Question 23

Which gene segments code for the heavy chain of BCRs?

Answer 23

V (variable), D (diversity), J (joining) - all 3

Question 24

How is the variable region of BCRs unique?

Answer 24

VDJ recombination means that multiple options can be selected for each gene segment leading to a huge number of possible gene combinations.

Question 25

Function of B cell negative selection

Answer 25

ensures there are no self reacting B cells circulating that will recognise and target self antigens

Question 26

Where does negative selection occur?

Answer 26

bone marrow

Question 27

How does negative selection occur?

Answer 27

specialised bone marrow cells present self antigens to B cells which are expressing antibodies/BCR (IgM, IgD)

Question 28

What happens if B cells do not bind to self antigens during negative selection?

Answer 28

B cells are released from the bone marrow and migrate to secondary lymphoid tissues

Question 29

What happens if BCR binds to the self antigen during negative selection?

Answer 29

the self-reacting B cell is engulfed and removed by macrophages

Question 30

How can autoimmune disease arise?

Answer 30

if there is a breakdown in negative selection (and self-reactive B cells are released)

Question 31

What are B cells called when they leave the bone marrow?

Answer 31

naive B cells (not yet encountered antigens)

Question 32

Examples of specialised lymphoid tissues

Answer 32

(found in barrier and mucosal sites) tonsils, adenoids, Peyer's patches

Question 33

What are the 2 types of B cell activation?

Answer 33

Thymus-dependent (requires help of T cells) and thymus-independent (without help from T cells)

Question 34

Which T cells enable thymus-dependent activation of B cells?

Answer 34

CD4+ TH2 cells and TFH (T follicular helper cells)

Question 35

How can B cells be activated without T cell involvement?

Answer 35

Thymus-independent activation - involves the BCR recognising an antigen, and the PRRs (e.g. TLR) on the B cell recognising a PAMP (component of microorganism e.g. LPS) at the same time

Question 36

What happens when naive B cells are activated?

Answer 36

They differentiate into plasma cells which initially releases IgM. Naive B cells also differentiate into memory B cells but only in thymus-dependent activation.

Question 37

How are B cells activated by thymus-dependent activation?

Answer 37

1. B cells present antigen to T cells (CD4+ TH2 and TFH cells) 2. Costimulatory molecules of B cell (CD40) and T cell (CD40L) interact 3. T cell releases cytokines which leads to B cell differentiation

Question 38

Which cells do B cells differentiate into during thymus-dependent activation?

Answer 38

plasma cells and memory B cells

Question 39

What cells do B cell differentiate into during thymus-independent activation?

Answer 39

plasma cells only

Question 40

Which type of B cell activation does not provide long-term immunity?

Answer 40

thymus-independent B cell activation because memory B cells are not produced

Question 41

What does B cells activation lead to?

Answer 41

class switching

Question 42

What is the first type of antibody produced by plasma cells following B cell activation?

Answer 42

IgM

Question 43

What is class switching?

Answer 43

When B cells change the production of antibodies from one type to another (IgM -> IgG)

Question 44

Why does class switching occur?

Answer 44

to produce a more effective immune response (IgM has a weak response, other antibodies have different functions too)

Question 45

How does class switching occur?

Answer 45

by gene rearrangement to alter the constant region which allows the production of antibodies with different structures but with the same antigen binding site

Question 46

What features determine the effectiveness of antibodies?

Answer 46

affinity and avidity

Question 47

What is the affinity of an antibody?

Answer 47

strength of binding to antigen

Question 48

What is the avidity of an antibody?

Answer 48

the number of binding sites the antibody has

Question 49

Which antibodies have low avidity?

Answer 49

IgD, IgM, IgE, IgG (only 2 antigen binding sites)

Question 50

Which antibodies have high avidity?

Answer 50

IgA (4 antigen binding sites) and secreted IgM (10 binding sites)

Question 51

What is the structure of secreted IgM?

Answer 51

pentametric complex - made of 5 antibodies so a total of 10 antigen binding sites

Question 52

Which antibodies have low affinity?

Answer 52

IgM, IgD, IgA

Question 53

Which antibodies have high affinity?

Answer 53

IgG and IgE (therefore are most effective and so are produced the most)

Question 54

What are the 5 types of antibodies / immunoglobulins?

Answer 54

IgM and IgD (BCRs), IgG, IgE, IgA

Question 55

Example of where secretory IgA is found

Answer 55

saliva

Question 56

What are the functions of B cell antibodies?

Answer 56

Neutralisation, opsonisation (tag microorganisms/allergens for removal), activate the complement cascade

Question 57

Which antibody has the function of neutralisation?

Answer 57

secretory IgA - binds to 4 antigens simultaneously and prevents microorganisms attaching to host cells.

Question 58

Function of opsonisation

Answer 58

antibodies (opsonins) tag microorganisms and allergens for removal which initiates phagocytosis (e.g. by macrophages) or degranulation (of NK, mast cells, eosinophils, basophils)

Question 59

Which pathway of the complement cascade can be activated by antibodies?

Answer 59

classical pathway

Question 60

What does the complement cascade produce?

Answer 60

Anaphylatoxins

Question 61

Functions of anaphylatoxins

Answer 61

recruit immune cells to the site of infection, form membrane attack complexes, drive opsonisation for phagocytosis

Question 62

Which cells play a role in vaccinations?

Answer 62

B and T cells (adaptive immune system)

Question 63

Which antibodies are produced in a primary response (e.g. vaccination)?

Answer 63

initially IgM which is then switched to IgG

Question 64

Which antibodies are produced in a secondary response?

Answer 64

Mainly IgG (and some IgM)

Question 65

Why is a much larger concentration of IgG released more rapidly in a secondary response?

Answer 65

memory B cells are primed to produce IgG upon re-exposure to a specific antigen