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1
Q

What is humoral immunity mediated by?

A

Antibodies

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2
Q

What is the difference between naive and activated B cells

A

Naive B cells recognise antigens but do not secrete antibodies

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3
Q

What surface antibodies do naive B cells have?

A

IgM and IgD

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4
Q

Draw out the antibody structure

A

4 polypeptide chains assembled into a Y shaped molecule
2 L chains
2 heavy chains
check

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5
Q

How many light chain types are there?

A

kappa and lambda

C domain is different, no functional differences

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6
Q

How many types of heavy chains are there?

A

5 different classes of heavy domains. They differ in their C domain and function.

This is what determines what classes antibodies can be divided into

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7
Q

Why is T independent antibody responses important?

A

It means pathogens with polysaccharides, lipids and other non-protein antigens could stimulate antibody production without T cell help

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8
Q

What antibodies are released in T independent Ab response?

A

IgM
almost no heavy chain isotype switching
no affinity maturation
no memory

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9
Q

What are properties of T dependent Ab responses

A

heavy chain isotype switching, affinity maturation, memory B cells and long-lived plasma cells

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10
Q

How are B cells activated in Thymus dependent activation of B cells?

A

Proliferation is induced by

1) antigen binding to the BCR-proteins (antigen specific)
2) Interaction between B cells and CD4+ T helper cell-co-stimulation (CD40-CD40L)
3) cytokines released by T helper cells

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11
Q

where do naive B cells move

A

naive B cells recirculate and enter follicles in secondary lymphoid tissues

In the secondary lymphoid tissues, they migrate into the B cell zones

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12
Q

How are Naive B cells attracted to specific places in the secondary lymphoid organ

A

Naive B cells are attracted to follicles via CXCL13 secreted by FDCs

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13
Q

how are antigens delivered into the lymph nodes?

A

Small antigens are delivered to the lymph nodes by afferent lymphatic vessels that drain the subscapular sinus

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14
Q

How are antigens delivered to follicles?

A

Subscapsular sinus macrophages capture large microbes and antigen antibody complexes and deliver these to follicles

Some large antigens are captured in the medullary region by resident Dendritic cells and are transported into follicles

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15
Q

How do immune complexes bind onto B cells or follicular dendritic cells?

A

They might bind on CR2 on B cells.

They bind to complement receptors.

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16
Q

Are antigens presented to B cells intact?

A

Yes, they are intact (native form), meaning they are not processed by APCs

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17
Q

How does the BCR activate the B cell

A

2 identical epitopes on aggregated protein antigen/repeated identical epitopes bind to adjacent immunoglobulin receptors to trigger B cell activation.
Receptor cross activation

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18
Q

How does signal transduction in B cells work?

A

Cross linking IgM and IgD receptors by antigen triggers signals that they are relayed across the cell membrane by Igalpha and Igbeta signal transducers

This causes the phosphorylation of ITAMS which initiates phosphorylation cascades.

These signal cascades activate enzymes and transcription factors for initiating gene expression and synthesis of proteins needed for B cell proliferation and differentiation

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19
Q

What are the characteristics of activated B cells

A

Proliferation
expansion of antigen specific clone
Increased expression of B7 co-stimulators

Express cytokine receptors

Increased expression of chemokine receptors

Low level of IgM secretion

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20
Q

Function of IgM

A

binds easily on polysaccharides, and could effectively cross link many B cell antigen receptors

Is an excellent activator of complement

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21
Q

How do antigen specific T helper cells and B cells get together?

A

They meet at the very edges of the follicles

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22
Q

Are BCRs apcs?

A

Yes, proteins could bind antigens via BCR and they could be processed and displayed on MHC class II in B cell membrane

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23
Q

What is T cell help

A

When CD40 L newly expressed on activated T cells binds to CD40 molecules expressed on B cells

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24
Q

What does the engagement of CD40L and CD40 do?

A

They help induce B cell proliferation
Antibody synthesis and secretion

They also initiate heavy chain isotype class switching and affinity maturation

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25
What are innate like T cells
They have T cell receptors
26
How are the TCR on Innate like T cells different
their TCR are invariant meaning that they have limited diversity and restricted repertoire of TCR compared to ab T cells
27
What do innate like T cells recognise
They recognise non-peptide antigens | Non polymorphic antigen presenting molecules (not MHC classes)
28
How fast do innate like T cells respond?
Very quickly
29
What is a semi invariant TCR
V regions are expressed, and there is little to no junctional diversity
30
What does the limited diversity of unconventional T cells mean?
It means that unconventional T cells won't need to clonally expand and are ready for a rapid response
31
Natural Killer T cell properties
They have MHC Class I like molecule: CD1d | They recognise lipid antigens
32
How are NKT cells different to conventional T cells
They respond to lipid based antigen presented by CD1d They exit the thymus with an antigen experienced phenotype= functionally mature They respond rapidly to TCR and/or cytokine signals causing immediate production of cytokines They are non-circulating
33
How are NKT cells similar to conventional T cells
Their subsets resemble CD4 T cell subsets They differentiate in thymus and periphery Can kill cells via perforin and granzyme B
34
What are 2 subsets of NKT cells
tissue homing and tissue resident Functional not clear one is homeostasis of gut One is homeostasis of adipose tissue
35
what are MAIT cells activated by?
activated by vitamin B intermediates | Vitamin B intermediates like riboflavin are importantly found in some bacteria
36
How are MAIT cells unique in how they detect an infection?
They detect infection based on a metabolic signature of a pathogen, and not a pathogen structure-whatever that means
37
Are mait cells functionally mature
yes, they exit the thymus with an antigen experienced phenotype
38
What are MAIT cell response to TCR signally?
immediate production of cytokines
39
What is thymic development of MAIT cells dependent on?
remote production of Vit B2 metabolites by commensal bacteria
40
gdT cells
unknowwn they apparently have an immune surveillance role and can respond rapidly by directly killing target cells or cytokine production.
41
what are some ligands of gdT cells
stress induced, empty or non-presenting MHC like molecules | Surface associated and soluble structures.
42
The Germinal Centre
Site of affinity maturation, isotype switching, generation of long lasting plasma cells and memory B cells
43
Where and how are germinal centers created?
They are created within lymphoid follicles during T dependent immune responses
44
What kind of cells are found in Germinal center
Each Germinal center contains B cells derived from one or a few antigen specific clones
45
In the dark zone of a GC, how many progeny could 1 lymphocyte give rise to?
5000 progeny. Progeny are small cells that undergo further differentiation and selection in the C light zone
46
Outline the germinal centre reaction
activated B cells migrate into follicle, proliferate and form the dark zone Once in the darkzone, B cells undergo extensive isotype switching and somatic hypermutation of IG V genes and migrate into the light zone In the light zone, they encounter follicular dendritic cells and T follicular helper cells B cells with the highest affinity receptors selected to survive finally they differentiate
47
What are the benefits of isotype class switching?
Different microbes are eliminated most efficiently by different immune responses.
48
What is the mechanism of heavy chain class switch
``` The CD40 engagement induces the enzyme AID-activation induced deaminase. AID is the pivotal enzyme for isotype class siwtching ```
49
where are gd T cells found?
They are present at the epithelial and mucosal barriers
50
What are ligands of gdT cells
phosphoantigens butyrophilins surface associated and soluble structures stress-induced empty or non-presenting MHC like molecules
51
phosphoantigens
small phosphorylated metabolites microbial phosphoantigen produced by bacteria. Some phosphoantigens are common in both prokaryotes and eukaryotes which may be upregulated in tumour cells and endogenous danger siganlls
52
Butyrophilins
Unclear, but apparent it is not a p-Ag antigen presenting molecule; it could be a co-factor pAg bind intracellular region of BTN3A1=> which may cause conformational change. A danger signal presented on the surface of infected or stressed cells in the presence of phosphoantigens
53
What are innate lymphoid cells?
These are lymphocytes which do not express diversified antigen receptors like T and B cells They are mostly tissue resident and respond to signals from tissue resident cells Fast-acting, but also around later for cross-talk with T cells
54
What are the functions of ILCs
They conduct the early defense against pathogens They recognise stressed and damaged host cells-help to clear, repair and rebuild They maintain tissue integrity and homeostasis
55
Give examples of what ILC 2 could do in tissue modelling, growth and repair
ILC2 could secrete IL13, which drives epithelial cells towards secretory lineages They secrete AREG which controls epithelial cell proliferation and differentiation needed for repair after pathogen expulsion
56
What does ILC3 do in tissue modelling, growth and repair
produce IL22 which could protect the epithelial barrier: promote proliferation and protect from apoptosis, instructs epithelial cells to make anti bacterial peptides
57
what could ILC2 do in tissue homeostasis
IL13 helps polarise M2 macrophages, regulate insulin resistance IL4 and IL13 beiges pre adipocytes
58
How do you activate naive CD8+ T cells
They mature and develop TCR in the thymus then naive but functionally inactive CTL (known as pre CTL) migrate from thymus to peripheral lymphoid tissue ``` The activation and generation of effector CTLs requires signal 1 and signal 2 Signal 1 TCR recognising antigenic peptides in association with MHC class 1 ```
59
How does T cells help activate naive CD8+ T cells unknown check
They could secrete cytokines that stimulate CD8+ T cell differentiation The antigen stimulated helper T cells express CD40 L which binds to CD40 on APCs
60
Does this mean CD8 T cells could be independently activated and if so, what is the difference?
unknown
61
what does the differentiation of CD8+ T cells into effector cells result in?
molecular events in CTL differentiation Transcription factors: T bet and eomesodermin Transcription factors contribute to high level expression of cytoplasmic granules and cytokines such as interferon gamma development of membrane bound cytoplasmic granules cytokine secreting capability
62
How does activated T cells know where to migrate/recognise sites of infection
Activation of CD8+ T cells lead to an upregulation of integrins, selectin ligands and chemokine receptors Endothelial cells at the site of infection are induced by cytokines such as TNF and IL-1 to express selectins and ligands for integrins
63
What are granzymes?
They are serine proteases that enter target cells Granzyme B is the most important of these enzymes, and they cause proteolytic cleavage after aspartate residues. Granzyme B's proteolytic cleavage activates caspases and helps induce apoptosis
64
What does fas ligand do?
unknown
65
What are NK cells
They are a subtype of type 1 innate lymphoid cell. They are large granular lymphocytes that do not express diverse, clonal antigen receptors
66
How are NK cells activated and proliferated
IL12 and IL15 cause proliferation of NK cells
67
What is the activating receptor of an NK cell
unknown check the lecture
68
What is the inhibiting ligand of the NK cell
``` An MHC class I it binds to receptors such as KIR, CD94/NKG2 ```
69
Function of IgM
They neutralise microbes/toxins activate classical pathway of complement about 6% in serum
70
FUnction of IgG
neutralisation of microbes and toxins opsinization of Ag for phagocytosis by macrophages and neutrophils antibody dependent cellular cytotoxicity by NK cells Feedback inhibition of B cell activation neonatal immunity activation of complement
71
function of IgA
Mucosal immunity | neutralisation of microbes/toxins in mucosal organs
72
IgE
mast cell degranulation eosinophil mediated defense against helminths Antigen receptor on naive B cells
73
FcgammaR (CD64) mediated effector functions
Opsonisation of antigen for phagocytosis Antibody dependent cellular cytotoxicity by NK cells feedback inhibition of B cell activation neonatal immunity By phagocyte FC receptors causes them to produce ROS, nitric oxide and hydrolytic enzymes
74
CD64 has the highest affinity for
IgG FC receptor for phagocytes
75
CD16
binds to IgG on cell surface | causes NK cells to release cytotoxic granules
76
What happens to simultaneous cross linking of inhibitory Fc gamma RII b and BCR
leads to phosphorylation of ITIM and blocks downstream signalling and proliferation. It is the checkpoint for activation and proliferation of autoreactive B cells or modulation of an immune response I think it is basically the same for isolated cross linking \
77
How are newborns protected against infection?
Maternal IgG transported across the placenta during pregnancy and some suggest IgE could also cross the placenta Maternal IgG and IgA is transported across the gut epithelium from breastmilk
78
How does IgG cross these barriers
actively transferred by the neonatal Fc receptor which is an MHC class 1 like molecule
79
How does FcRn mediate directional transport?
so, it's pH dependent The direction is from maternal blood to placenta to fetal blood. ``` Physiological pH (maternal IgG is taken up to endosomes) then the acidic pH causes high affinity binding of Fc region of IgG to FcRn as endosomes are acidified ``` then the physiological pH in fetal circulation promotes dissociation
80
FcRn functions
helps transfer of breast milk derived IgG from intestinal lumen to neonatal blood In adults, they have a role in transporting IgG across polarised barriers in adult tissues In the gut, IgG transported into the lumen and then IgG immune complexes transported back IgG immune complexes taken up by FcgammaR on DC to create tolerance against food antigen and immune response to pathogen This recycles Igg through endosomes of epithelial cells or monocytes to keep IgG in serum for longer
81
outline IgA structures
IgA dimers are held together by the J chain and the dimer is transported across epithelium into the lumen by the poly Ig receptor made by mucosal epithelial cells Also called transcytosis it neutralises toxins and viruses, blocks colonization and entry of pathogens and commensals the FcAR are expressed on cells of myeloid lineage, including kupffer cells in the liver cross linking of FcARI by IgA immune complexes or IgA opsinized pathogens induces phagocytosis and activation of FcaRI bearing cells
82
What are monoclonal antibody therapy used for
1) triggering target cell death 2) agonist: stimulate signalling 3) antagonist: block receptors or ligands
83
Antibody engineering
enhance or minimize Fc mediated functions add effector functions extend half-life optimise antigen binding

immu3102 (12 decks)

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