Block C Lecture 3: Activating T Cells and B Cells

Question 1

What type of interaction is the physical interaction between T cells and APCs?

Answer 1

A cognate interaction (direct cell-cell interaction)
(Lecture 3, Slide 4)

Question 2

Why is the cognate interaction between CD (T cells) molecules and MHC molecules in the T-cell APC cognate interaction critical to mounting an effective immune response?

Answer 2

As it helps activates T cells
(Lecture 3, Slide 6)

Question 3

What type of cells do cytotoxic (CD8+) T cells kill?

Answer 3

Virally infected cells
(Lecture 3, Slide 6)

Question 4

What 3 things are involved in the cognate interaction in CD8+ T cell effector function?

Answer 4

It involves MHC class 1, TCR (with CD8), and a costimulatory signal (B7-CD28)
(Lecture 3, Slide 8)

Question 5

What signals does the Antigen-Presenting Cell (APC) send to CD8+ T cells after antigen recognition?

Answer 5

Signals for proliferation
(Lecture 3, Slide 8)

Question 6

What 2 ways do APCs send proliferation signals after cytotoxic (CD8+) T cells have recognised the antigen?

Answer 6

Upregulation of the IL-2 receptor
Production of its own IL-2
(Lecture 3, Slide 8)

Question 7

What does upregulation of IL-2 receptor mean?

Answer 7

The cell expresses more of the receptor in response to a specific signal, in this case a proliferation signal sent by an APC
(Lecture 3, Slide 8)

Question 8

How does IL-2 cytokine act as a signal for proliferation to cytotoxic (CD8+) T cells?

Answer 8

By binding to its receptors on the T cell
(Lecture 3, Slide 8)

Question 9

What does the IFNγ (interferon gamma) signal instruct cytotoxic (CD8+) T cells to do?

Answer 9

Differentiate and kill
(Lecture 3, Slide 8)

Question 10

What 4 things are involved in a Th2 cell interacting with a B cell?

Answer 10

Th2 T cell, B cell, BCR, MHC Class II receptor (with co-stimulation from CD40-CD40-L)
(Lecture 3, Slide 9)

Question 11

What is the purpose of a Th2 cell interacting with a B cell?

Answer 11

In order to help the B cell proliferate
(Lecture 3, Slide 9)

Question 12

What 3 cytokines do Th2 cells secrete after interacting with B cells, in order to get B cells to proliferate?

Answer 12

IL-4, IL-5 and IL-6
(Lecture 3, Slide 9)

Question 13

What 2 things can B cells differentiate into after being signalled to proliferate by a Th2 cell?

Answer 13

Resting memory cells or antibody secreting plasma cells
(Lecture 3, Slide 9)

Question 14

What are the functions of Th1 and Th2 helper T cells?

Answer 14

Th1 secretes IFNγ (interferon gamma) and activates macrophage function
Th2 secretes IL-4 and helps antibody production by activating B cells
(Lecture 3, Slide 10)

Question 15

What are 3 types of helper (CD4+) cells, other than Th1 and Th2 cells?

Answer 15

Th17
TFH
Treg
(Lecture 3, Slide 11)

Question 16

What is the function of Th17 helper (CD4+) T cells?

Answer 16

The are important in the response to extracellular bacteria and lead to production of neutrophils
(Lecture 3, Slide 11)

Question 17

What is the function of TFH helper (CD4+) T cells and where are they found?

Answer 17

They are found in the follicles (germinal centres) and are important to help B cells produce antibodies
(Lecture 3, Slide 11)

Question 18

What is the function of Treg helper (CD4+) T cells?

Answer 18

They downregulate immune responses and help prevent harmful immune responses or autoimmunity
(Lecture 3, Slide 11)

Question 19

What is differentiation of T cells regulated by?

Answer 19

Cytokines
(Lecture 3, Slide 12)

Question 20

What 2 things does recognition of an antigen by a BCR result in?

Answer 20

Activation of the B cell and internalisation of the antigen
(Lecture 3, Slide 17)

Question 20

What happens when a B cell activates?

Answer 20

It secretes antibody of the same specificity of its BCR
(Lecture 3, Slide 16)

Question 20

What happens after a B cell expresses its functional BCR?

Answer 20

It matures from the primary bone marrow and migrates to the periphery via the lymph nodes
(Lecture 3, Slide 16)

Question 21

What happens after the antigen is internalised in B cells?

Answer 21

The antigen is broken down into peptides
(Lecture 3, Slide 17)

Question 22

What happens after the antigen is broken down into peptides in B cells?

Answer 22

The peptides are loaded into MHC Class II receptors within the B cell and presented to antigen-specific helper (CD4+) T cells
(Lecture 3, Side 17)

Question 23

What happens after B cells present antigens to helper (CD4+) T cells?

Answer 23

If the T cell also recognises the antigen it provides help to the B cell via cytokines and co-stimulation (Lecture 3, Slide 17)

Question 24

What do helper T cells allow B cells to do?

Answer 24

Fully activate and secrete antibodies (Lecture 3, Slide 17)

Question 25

What happens to the BCR after it recognises an antigen?

Answer 25

It undergoes endocytosis and gets degraded with the antigen (Lecture 3, Slide 18)

Question 26

How do dendritic cells play a part in antigen recognition?

Answer 26

As it can uptake the antigen, break it down and present it to helper (CD4+) T cells via MHC class II receptors (Lecture 3, Slide 20)

Question 27

What is the structure of an antibody?

Answer 27

It is a multi-unit protein consisting of 2 copies of 2 types of chains, a heavy chain and a light chain, with disulphide bonds to link these chains. It consists of 2 main regions - a variable region and a constant region (Fc region) (Lecture 3, Slide 22)

Question 28

What antibody region binds to the specific antigen?

Answer 28

The variable region (Lecture 3, Slide 23)

Question 29

What is the site the antibody binds to known as?

Answer 29

The epitope (Lecture 3, Slide 23)

Question 30

What 2 things can an epitope be?

Answer 30

A linear sequence or based on antigen folding (Lecture 3, Slide 23)

Question 31

What is the purpose of the "hinge" region of antibodies and what does this allow?

Answer 31

It gives the antibody flexibility and allows the antibody to form various immune complexes (Lecture 3, Slide 24)

Question 32

What are the 3 main functions of an antibody?

Answer 32

Neutralisation Opsonisation Complement (Lecture 3, Slide 25)

Question 33

What do the neutralisation, opsonisation and complement functions of antibodies depend on?

Answer 33

Antigen-specific binding of the variable region (Lecture 3, Slide 25)

Question 34

What are the 5 main isotypes of antibodies in humans?

Answer 34

IgA, IgD, IgE, IgG, and IgM (Lecture 3, Slide 25)

Question 35

What do the functions of the constant region of an antibody depend on?

Answer 35

Its isotype (Lecture 3, Slide 25)

Question 36

What is neutralisation?

Answer 36

An antibody binds bacterial (or other toxins), preventing the interaction of the toxin with its target protein and thus preventing damage, afterwards, the antibody complexes can then be ingested by a macrophage and destroyed (Lecture 3, Slide 26)

Question 37

What is opsonisation a response to?

Answer 37

Bacteria in the extracellular space (Lecture 3, Slide 27)

Question 38

What happens in opsonisation?

Answer 38

Antibodies bind to the surface of the bacteria, coating them, the constant region of the antibody is free to interact with Fc receptors on the surface of macrophages, triggering the ingestion and destruction of the bacteria (Lecture 3, Slide 27)

Question 39

What is complement activation a response to?

Answer 39

Bacteria present in plasma (Lecture 3, Slide 28)

Question 40

What is complement?

Answer 40

A cascade of enzymes which punch holes in cell membranes by assembling a membrane attack complex (MAC) (Lecture 3, Slide 28)

Question 41

What occurs in complement activation?

Answer 41

Antibodies coat the pathogen (like in opsonisation) but this time recruit complement proteins which puncture and kill the pathogen, with the remains of the bacteria being able to be taken up by a macrophage (Lecture 3, Slide 28)

Question 42

What 2 antibodies can neutralise toxins and block the infectivity of viruses and bacteria?

Answer 42

IgA and IgG (Lecture 3, Slide 29)

Question 43

How can antibodies block a virus binding to a cell surface and releasing its own DNA into a cell?

Answer 43

By binding to the virus receptor and preventing entry (Lecture 3, Slide 29)

Question 44

What initiates the complement cascade in the classical pathway?

Answer 44

Antigen-antibody complexes binding to complement component C1q (Lecture 3, Slide 30)

Question 45

How does the tertiary structure of antibodies contribute to the activation of complement via the classical pathway?

Answer 45

IgM is most stable as a pentamer, meaning it can bind many antigens at the same time, meaning only one single structure is required for C1q binding, whereas IgG exists as a monomer, meaning multiple IgGs are required to bind C1q (Lecture 3, Slide 30)

Question 46

What role does complement play in opsonisation?

Answer 46

Complement can bind to complement receptors on the surface of macrophages after the constant region of the antibody binds Fc receptors (Lecture 3, Slide 31)

Question 47

What are the structures of all 5 isotypes of Ig antibodies?

Answer 47

IgA - Monomer or dimer IgD - Monomer IgE - Monomer IgG - Monomer IgM - Pentamer (Lecture 3, Slide 33)

Question 48

What is the cytokines produced by a helper (CD4+) cell associated with and what does this result in?

Answer 48

The isotype of the antibody secreted by a B cell and in turn determines the responses activated and therefore the consequences (Lecture 3, Slides 35 and 36)

Question 49

How are different cell types activated by different antibody isotypes?

Answer 49

As different cell types express different Fc receptors (Lecture 3, Slide 37)

Question 50

What Fc receptor do mast cells express and what antibody does this bind?

Answer 50

FceR1 which binds IgE (Lecture 3, Slide 37)

Question 51

How can IgE result in anaphylaxis?

Answer 51

When IgE binds to an antigen it cross links FceR1receptors and this results in degranulation of mast cells, resulting in analphylaxis (Lecture 3, Slide 37)

Question 52

What Fc receptor do macrophages express and what antibody does this bind?

Answer 52

FcgR receptors which only binds IgG (Lecture 3, Slide 37)

Question 53

How does IgG binding to a FcgR receptor on a macrophage result in it engulfing and destroying a pathogen?

Answer 53

As the FcgR receptors crosslink, which activates the macrophage (Lecture 3, Slide 37)