Block C Lecture 3: Activating T Cells and B Cells Flashcards
What type of interaction is the physical interaction between T cells and APCs?
A cognate interaction (direct cell-cell interaction)
(Lecture 3, Slide 4)
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?
As it helps activates T cells
(Lecture 3, Slide 6)
What type of cells do cytotoxic (CD8+) T cells kill?
Virally infected cells
(Lecture 3, Slide 6)
What 3 things are involved in the cognate interaction in CD8+ T cell effector function?
It involves MHC class 1, TCR (with CD8), and a costimulatory signal (B7-CD28)
(Lecture 3, Slide 8)
What signals does the Antigen-Presenting Cell (APC) send to CD8+ T cells after antigen recognition?
Signals for proliferation
(Lecture 3, Slide 8)
What 2 ways do APCs send proliferation signals after cytotoxic (CD8+) T cells have recognised the antigen?
Upregulation of the IL-2 receptor
Production of its own IL-2
(Lecture 3, Slide 8)
What does upregulation of IL-2 receptor mean?
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)
How does IL-2 cytokine act as a signal for proliferation to cytotoxic (CD8+) T cells?
By binding to its receptors on the T cell
(Lecture 3, Slide 8)
What does the IFNγ (interferon gamma) signal instruct cytotoxic (CD8+) T cells to do?
Differentiate and kill
(Lecture 3, Slide 8)
What 4 things are involved in a Th2 cell interacting with a B cell?
Th2 T cell, B cell, BCR, MHC Class II receptor (with co-stimulation from CD40-CD40-L)
(Lecture 3, Slide 9)
What is the purpose of a Th2 cell interacting with a B cell?
In order to help the B cell proliferate
(Lecture 3, Slide 9)
What 3 cytokines do Th2 cells secrete after interacting with B cells, in order to get B cells to proliferate?
IL-4, IL-5 and IL-6
(Lecture 3, Slide 9)
What 2 things can B cells differentiate into after being signalled to proliferate by a Th2 cell?
Resting memory cells or antibody secreting plasma cells
(Lecture 3, Slide 9)
What are the functions of Th1 and Th2 helper T cells?
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)
What are 3 types of helper (CD4+) cells, other than Th1 and Th2 cells?
Th17
TFH
Treg
(Lecture 3, Slide 11)
What is the function of Th17 helper (CD4+) T cells?
The are important in the response to extracellular bacteria and lead to production of neutrophils
(Lecture 3, Slide 11)
What is the function of TFH helper (CD4+) T cells and where are they found?
They are found in the follicles (germinal centres) and are important to help B cells produce antibodies
(Lecture 3, Slide 11)
What is the function of Treg helper (CD4+) T cells?
They downregulate immune responses and help prevent harmful immune responses or autoimmunity
(Lecture 3, Slide 11)
What is differentiation of T cells regulated by?
Cytokines
(Lecture 3, Slide 12)
What 2 things does recognition of an antigen by a BCR result in?
Activation of the B cell and internalisation of the antigen
(Lecture 3, Slide 17)
What happens when a B cell activates?
It secretes antibody of the same specificity of its BCR
(Lecture 3, Slide 16)
What happens after a B cell expresses its functional BCR?
It matures from the primary bone marrow and migrates to the periphery via the lymph nodes
(Lecture 3, Slide 16)
What happens after the antigen is internalised in B cells?
The antigen is broken down into peptides
(Lecture 3, Slide 17)
What happens after the antigen is broken down into peptides in B cells?
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)
What happens after B cells present antigens to helper (CD4+) T cells?
If the T cell also recognises the antigen it provides help to the B cell via cytokines and co-stimulation
(Lecture 3, Slide 17)
What do helper T cells allow B cells to do?
Fully activate and secrete antibodies
(Lecture 3, Slide 17)
What happens to the BCR after it recognises an antigen?
It undergoes endocytosis and gets degraded with the antigen
(Lecture 3, Slide 18)
How do dendritic cells play a part in antigen recognition?
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)
What is the structure of an antibody?
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)
What antibody region binds to the specific antigen?
The variable region
(Lecture 3, Slide 23)
What is the site the antibody binds to known as?
The epitope
(Lecture 3, Slide 23)
What 2 things can an epitope be?
A linear sequence or based on antigen folding
(Lecture 3, Slide 23)
What is the purpose of the “hinge” region of antibodies and what does this allow?
It gives the antibody flexibility and allows the antibody to form various immune complexes
(Lecture 3, Slide 24)
What are the 3 main functions of an antibody?
Neutralisation
Opsonisation
Complement
(Lecture 3, Slide 25)
What do the neutralisation, opsonisation and complement functions of antibodies depend on?
Antigen-specific binding of the variable region
(Lecture 3, Slide 25)
What are the 5 main isotypes of antibodies in humans?
IgA, IgD, IgE, IgG, and IgM
(Lecture 3, Slide 25)
What do the functions of the constant region of an antibody depend on?
Its isotype
(Lecture 3, Slide 25)
What is neutralisation?
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)
What is opsonisation a response to?
Bacteria in the extracellular space
(Lecture 3, Slide 27)
What happens in opsonisation?
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)
What is complement activation a response to?
Bacteria present in plasma
(Lecture 3, Slide 28)
What is complement?
A cascade of enzymes which punch holes in cell membranes by assembling a membrane attack complex (MAC)
(Lecture 3, Slide 28)
What occurs in complement activation?
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)
What 2 antibodies can neutralise toxins and block the infectivity of viruses and bacteria?
IgA and IgG
(Lecture 3, Slide 29)
How can antibodies block a virus binding to a cell surface and releasing its own DNA into a cell?
By binding to the virus receptor and preventing entry
(Lecture 3, Slide 29)
What initiates the complement cascade in the classical pathway?
Antigen-antibody complexes binding to complement component C1q
(Lecture 3, Slide 30)
How does the tertiary structure of antibodies contribute to the activation of complement via the classical pathway?
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)
What role does complement play in opsonisation?
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)
What are the structures of all 5 isotypes of Ig antibodies?
IgA - Monomer or dimer
IgD - Monomer
IgE - Monomer
IgG - Monomer
IgM - Pentamer
(Lecture 3, Slide 33)
What is the cytokines produced by a helper (CD4+) cell associated with and what does this result in?
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)
How are different cell types activated by different antibody isotypes?
As different cell types express different Fc receptors
(Lecture 3, Slide 37)
What Fc receptor do mast cells express and what antibody does this bind?
FceR1 which binds IgE
(Lecture 3, Slide 37)
How can IgE result in anaphylaxis?
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)
What Fc receptor do macrophages express and what antibody does this bind?
FcgR receptors which only binds IgG
(Lecture 3, Slide 37)
How does IgG binding to a FcgR receptor on a macrophage result in it engulfing and destroying a pathogen?
As the FcgR receptors crosslink, which activates the macrophage
(Lecture 3, Slide 37)
