PA20292 Christine Edmead Flashcards
What do peritoneal lymphocytes secrete antibodies against?
Lipoplysachharides (LPS)
2 proinflammatory cytokines to remember;
IL1 (interleukin 1)
TNFalpha
These enhance Inflammatory response by drawing WBC’s out blood Into tissue to fight the antigen.
Some features of neutrophils?
Granulocytes Lysosomes inside Large multi lobed nucleus Lot of organelles Contain antmicrobial enzymes phagocytose
Features of macrophages?
Granulocyte Rounded nucleus Secrete cytokines Phagocytose Lots of organelles Inflammatory mediators Complement proteins Help with antigen presentation
Features of dendritic cells?
Large cell Small nucleus Membrane protrusions; engulf antigens Antigen presentation Release cytokines
What do dendritic, macrophages and neutrophils have in common?
They are reactive oxygen and nitrogen species.
All engulf the antigen
What do natural killer cells do?
Lysis of virally infected cells
Recognise viral antigens on cell surface
What are both natural killer cells and dendritic cells?
INTERFERONS
Interfere with viral reproduction
Basic job of pattern recognition receptors?
Recognise structures on microbes that aren’t present on self proteins.
Present of neutrophils macrophages and dendritic cells.
4 types
What are the 4 types of patter recognition receptors?
Mannose receptors- recognise sugars
Receptors for opsonins- enhance phagocytosis
Toll like receptors- recognise proteins on AG
7transmembrane alpha helical receptors - recognise peptide fragments
What happens when an antigen binds to pattern recognition receptors?
Phagocytosis by macrophages/ neutrophils
Cell may be killed by NK cells if virus
Presentation of fragments of AG to T cells by APC’s
What kind of things will toll like receptors respond to?
LPS- KEY ACTIVATORS
ds RNA
Bacterial peptidoglycans
These all tell them that the microbe is foreign
What does binding to toll like receptors result in?
Up regulation of inflammatory gene expression! Ie INFLAMMATION
What do TNFa , IL-1, E-selectin, and iNos result in?
Enhance white blood cell movement from blood to tissue to create inflammation
What is IL-12? Secreted by?
A cytokine
By macrophages and dendritics
T cell stimulating factor
Lipopolysaccharides are also known as….
ENDOTOXINS
What are LPS a product of/ found in?
Cell walls of gram NEGATIVE bacteria
What does LPS present of the surface of some bacteria stimulate?
Local and systemic inflammation WBCs leave blood to enter tissues Increase tissue fluids Increase cellular activators enzymes Activate macrophages and neutrophils Macrophage activation= cytokine release Reactive oxygens burst- involved with digestion of AG
What does excessive LPS stimulation cause?
Systemic inflammatory response syndrome (fever, septic shock, too much inflammation)
What are the effects of microbes binding to toll like and mannose receptors?
Production of CYTOKINES
Reactive oxygen intermediates; v. Toxic to microbes= kill the microbe
Phagocytosis
What can bind to 7 alpha helical transmembrane receptors?
Chemokines
Lipid mediators
N formyl methyl peptides (bacterial peptides)
Effect of binding to 7 alpha helical transmembrane receptors?
Increased integrin avidity (higher affinity of integrin receptors)
Stimulated migration into tissue
Does not result in killing of the microbe!!!!
Must abundant type of WBC?
Neutrophils
Small so they can easily enter tissues
What do natural killer cells recognise microbial markers on the surface of?
Already infected cells usually viral (not on microbes)
Recognise through patter recognition receptors
How do NKCs work?
Perforins released- make holes in target cell membrane
This allow entry of granzyme (digestive enzyme)
Infected cell is sacrificed and dies by apoptosis
Destroys viral load (target cells for NKCs are virally infected)
Apoptosis not phagocytosis!
How are NKcs activated ?
IL-12 from macrophages
Activates NKCs, they secrete IFNy
IFNy Feeds back and activates macrophage
(positive feedback loop)
How is NKCS actions inhibited?
By MHC Class I binding to inhibitory receptors on surface of NKCs.
Stops it invading any uninflected healthy self cells.
M N O P…. alphabet…..
Macrophages and neutrophils ….. Phagocytosis!
Remember…
Natural killer cells cause Virally infected cell to die by APOPTOSIS, due to entry of granzyme through pores made by perforins.
Not phagocytosis!!!! ( like macrophage and neutrophil )
All 4 cells of the innate system use______ receptors. What are these 4 cells?
Pattern recognition receptors.
Macrophages, neutrophils, dendritic cells, natural killer cells
What is the name of the components of a compliment system?
Zymogens
3 ways the complement cascade can be activated?
Classical
Alternate
Lectin
Classical pathway of complement cascade involves…..
C1 detects an ANTIBODY bound to the microbe
Then it cleaves C2/C4 starts the cascade…
Alternate complement pathway involves….
Direct recognition of a microbe
similar to using pattern recognition receptors
The lectin complement cascade pathway involves…..
Mannose receptor binding to lectin and cleaving C4
What do all 3 complement pathways result in the cleavage of?
C3——–> C3a + C3b
C3b leads to cleavage of C5——–> C5a + C5b
What do the complements C3a and C3b result in?
C3a resulting in INFLAMMATION drawing WBCs into tissues
C3b coats the microbe and enhances phagocytosis by opsonisation
What effect does the complement C5a have?
It is chemotactic for neutrophils (WBCs)
Draws them out of blood into tissues of infected site
Is the complement cascade part of the innate or adaptive immune system?
Innate.
It naturally occurs whenever a microbe attacks to trigger other proteins to do their jobs such as neutrophils.
What are the cytokines IL-1 and TNF produced by?
Macrophages that have been activated by LPS
These are PROINFLAMMATORY
This is why an inflammatory response occurs with bacteria but not viruses.
Because bacteria contain LPS activating infflamation.
What is IL-12 produced by and what is its actions?
Produced by macrophages and dendritic cells
Promote natural killer cell cytolysis
It also stimulates the production if IFNy in T cells and NKCs
What does IFNy do?
Stimulates a macrophage to kill a microbe
What type of immunity do B cell produce?
Humoral immunity
Means antibody mediated immunity
In the adaptive immune system, what are most cytokines produced by?
T cells
Cytokines of the adaptive immune system?
IL- 2, 4 ,5, 13
IFNy (both adaptive and innate)
TGFbeta [inhibitory]
TNFbeta
What is the lymphocyte repertoire?
Range of receptors able to recognise antigens in order for SPECIFIC RECOGNITION
T helper cells surface molecule is___
CD4
Cytotoxic T cells surface molecule is___
CD8
What do T helper cells and cytotoxic T cells both contain on their surfaces?
T cell receptors
Why do we say T cells have cell mediated immunity?
Because they secrete cytokines to activate other cells
What do lymphocytes have a large nucleus?
Involved with a lot of DNa transcription to make cytokines and antibodies
When activated, T cells swell in size. We call this _____
Blasting
When activated, B cells swell in size. We call them _____
Plasma cells
Produces large numbers of antibodies
What cells do APCs present AG fragments to?
T cells
What cells act as APCs?
Dendritic cells (main type)
B cells
Macrophages
What can heamopoeitic stem cells form?
RBC’s, myeloid cells, lymphocytes
What are bone marrow and the thymus classed as?
Primary lymphoid organs
T cells produced in bone marrow, mature in thymus
B cells produced and mature in bone marrow
What are lymph nodes classed as?
Secondary lymphoid organs
Once B and T cells are mature but naive, they migrate to the lymph nodes
What do B and T cells become on activation? ____ ___
Effector cells
Where are AGs that enter the body/ AG’s that are blood Bourne get taken?
AGs that enter the epithelia get taken to the lymph node via the lymphatics
AGs that are blood borne are carried to the spleen ( similar to lymph nodes, cleans the blood)
Spleen and lymph nodes= secondary lymphoid organs
What do activated Tc cells target?
Viruses!
Tc cells kill virally infected cells by apoptosis
Actions of T helper cells?
Activation of macrophages
Triggers phagocytosis
Enhance recruitment of neutrophils
What does IL-2 stimulate?
Growth factor of T cells, increases their number
IL 4 & 5 job?
Activate B cells to produce antibodies
IFNy job?
Secreted by T helper cells
Activates cytotoxic T cells and macrophages
TGF beta job?
Inhibitory cytokine
Acts to dampen the immune system and restore homeostasis (Like Treg cells)
What is the adaptive immune system triggered by?
The innate immune system
Which immune system are pattern recognition receptors and LPS involved in?
Innate immune system
Does the receptors involve in the immune response affinity for AG increase or decrease during the response?
Increase!
Antibodies provide active and passive immunity. What does this mean?
Active; antigens given as a vaccine are killed off by antibodies. Antibodies learn how to target antigen in case of further infection.
Active = you actively make the antibodies YOURSELF
Passive: immunity to a certain antigen has been passed on from genetic traits. (inherited)
IT IS THE TRANSFER OF AN ANTIBODY FROM ONE INDIVIDUAL TO ANOTHER.
Don’t make the AB yourself.
How much of plasma proteins do antibodies take up?
20%
What classes can the 2 heavy chains of antibodies be?
Class A, D, E, G or M
2 light chains of antibodies can be what classes?
Kappa and lambda
These are the classes of the light chains constant region.
What does each chain of an anti body have?
What do heavy chains have that light chains don’t?
All chains have several Ig domain repeats
All chains have variable , joining and conserved (constant) regions
Heavy chains also have diversity regions
What antibody class are produced on first antigen encounter? What are these for?
IgM
For complement activation
These are natural ABs in the lining of the abdominal cavity(peritoneum)
Remember IgM= complEMent activation
What are class IgD antibodies for?
B cell receptors
On surface of B cells
What are igA Antibodies for?
These target airborne antigens
Present at epithelial / mucosal surfaces (as this is where airborne antigens target)
Remember A for airborne
Generally found in lungs (we inhale airborne ABs)
What are IgE antibodies for?
For targeting parasites and immediate hypersensitivity (allergeeeee reactions= E)
Why are IgG antibodies so important?
Most abundant AB type in the circulation For secondary immune responses Microbes coated in IgG - opsonisation and complement activation AB dependent cell mediated cytotoxicity IgG provide Foetus with humoral immunity
What shapes do each of the different classes of antibodies have? Ie monomer, dimer….
Monomers= IgE IgG Dimers = IgA Pentamers= IgM
What does high avidity of an AB mean?
They can bind a large number of AG’s as they may be pentameric and have several binding sites, but usually bind with weak affinity.
Eg IgMs pentomer
How many different ABs can be made through gene rearrangement in order to recognise specific antigens?
10^7
What can the 5 constant regions of the heavy chains in ABs be?
IgA, D, M, G E. depends what class antibody you want to make.
What do the enzymes recombinases do in antibody production?
Bring together the single V, J and D (depending on if it’s light chain) alleles to make the required AB, then add on the constant region at a later stage.
They SPLICE DNA
Joining the constant region at the later mRNA stage in AB production, what does this allow?
Class switching at the later stages
The constant region of the heavy chain determines whether it’s Ig A D M E or G
What happens to make 2 required regions sit next to each other in antibody production?
The DNA/ alleles in between in spliced out by recombinase enzymes.
What are hypervariable regions also known as?
CDRs- complementary determining regions.
What are complemtary determining regions?
3 regions within variable gene segments with highly variable amino acid sequences.
CDR 1,2,3
Combining CDRs from heavy and light chains increases the diversity of ABs allowing them to bind to diff AGs
Also known as hypervariable regions and are particularly susceptible to mutations
What happens if a CDR undergoes a mutation?
Changes the affinity of an antibody for an antigen
What are hypervariable regions particularly susceptible to?
Mutations
Where does an antigen bind to an antibody?
At the ends of the Y shape.
Antigen binds in the groove between where heavy and light chains connect.
Variable regions of genes lie here, make antibody specific.
The rest of antibody usually have same structure as all others, apart from the Fc region.
Hypervariable regions also in the groove susceptible to mutations.
What makes an antibody specific, regarding its structure?
The variable gene region in the binding groove.
Also hypervariable regions in the groove that easily mutate.
Also nucleotides at junctions between V D and J regions can change increasing diversity further.
What are heavy and light chains bound togetherby?
Disulfidebonds
Where are the hypervariable regions located?
They protrude into the antigen binding groove.
What would mutations in gene sequences anywhere around the variable region of an antibody cause?
Change the shape of the antigen binding groove.
Causes the antibody to have a different affinity for the antigen.
CDR mutations (hypervariable regions) can result in this.
Why do antibodies remain specific to a certain antigen for the rest of its life?
Because B cells undergo irreversible gene recombination to make it specific to a particular antigen, it can’t change after this recombination as its irreversible.
As a B cell matures, what class does it change from the starting IgM class to?
IgD class
What triggers Ig class switching?
Activation of a B cell
Do IgG and IgE antibodies have low or high avidity?
Low
They are monomers
Only have 2 antigen binding sites
But will have HIGH affinity
What is a somatic hyper mutation in an antibody?
A mutation in the hyper variable region of the binding groove/ in the amino acids that lie there.
How many ABs do plasma B cells usually hold?
Around 2000.
What happens to B cells AB avidity to antigens as they mature?
As they mature, the B cell switches classes (from IgM)
The avidity decreases
Their affinity to antigens increases with more mature B cells.
Less mature= igM = 10 binding sites, pentameric, High avidity.
At first, before the B cells matured, what constant regions of the antibody are present?
All constant regions present at first coding for each class (C- A,G,M,D,E) Remember AB starts as IgM Then when class switching occurs, unwanted constant regions are spliced out.
In antibody production, splicing of RNA occurs until ____ is produced. What then needs to happen?
RNA spliced until mRNA (mature RNA) produced.
Then translation of this mRNA into a protein making the antibody occurs.
igG antibodies are most abundant. Where Are these usually found?
In the circulation.
What is the Fc region of an antibody coded for by?
The constant region of the heavy chain codes for Fc region. Ig class therefore determines it.
What does Fc region stand for?
Fragment crystallisable region.
Where does the Fc region of IgG antibodies bind? What does this promote?
To Fc receptors on surfaces of neutrophils and macrophages.
Promotes phagocytosis
Both AB and AG are destroyed.
What does the Fc region of IgE antibodies binding to Fc receptors result in?
Eosinophil activation (WBCs responsible for killing parasites) and mast cell degranulation, resulting in histamine release. igEs associated with allergies.
What kind of domains do Fc regions contain?
CONSTANT domains
How do IgG and IgM trigger complement activation?
By binding C1q
What are antigens recognised by on T cells and B cells?
TCRs on T cells ( T cell receptors)
Antibodies on B cells
The small part of an antigen that an antibody/ T cell receptor recognises is the _____
Epitope
Antibodies have different specificifities for different epitopes
One antigen lots of different epitopes= (a polyclonal) as lots of diff ABs respond
You can get a mixture of antibodies recognising different parts of one big antigen. These parts are ____ and this is a ____ response.
Epitopes
Polyclonal response
The part of an antibody that recognises a single epitope is the ____
Paratope
Do therapeutic antibodies tend to be polyclonal or monoclonal?
Monoclonal
Act against one particular epitope of an antigen
Activation of a single B cell= monoclonal response
An antibodies specificity for an antigen never changes. Ie the antigen it targets will always be the same. However, what can change?
The antibodies AFFINITY for the antigen can change,
due to the hyper variable regions in the binding groove.
Most effector responses are carried out by the Fc region of an antibody. this is because…….
This region binds the Fc receptors on target cells such as neutrophils and macrophages.
What can antibodies target? Bacteria , viruses, both?
Both bacteria and virus antigens!
Who were vaccinations discovered by and when?
By EDWARD JENNER
IN 1976
What are adjuvants?
Activate the immune system
Included in vaccinations
Enhance the recipients immune response to a given non pathogenic antigen.
Help lots of antibodies to be produced.
What kinds of things can you attach to an antibody to target an antigen?
Liposomes
Toxins
Radionuclides
Cytokines
Herceptin, does the antibody target and bind to receptor or ligand to stop ligand binding?
Receptor
Infliximab, does the antibody target and bind to receptor or ligand to stop ligand binding?
Ligand
What does ADEPT stand for?
Antibody directed enzyme prodrug therapy.
What does the anti-TNF antibody do?
Mops up excess TNF
Antibody binds to the LIGAND TNF
Stops receptor binding and TNF activating inflammatory responses.
Used in conditions where you want to reduce inflammation eg, arthritis
Example drug: INFLIXIMAB
Remember TNF is proinflammatory
What does the anti HER2 receptor antibody do? What’s this drug called?
This antibody binds to the HER2 recptor blocking ligand binding.
Stops receptor activation- stops cell growth and proliferation.
Drug = herceptin.
Used to treat BREAST CANCER
What cells is MHC protein present on?
Every cell apart from RBC’s
How is a B cell told that enough antibodies have been produced and deactivated?
Signal downregulated by when the Fc region of antibody binds back onto the Fc receptor of the B cell telling it to stop producing antibodies.
How is the signal of an antigen binding to a B cell enhanced?
Hint; what 2 things present on the B cell surface enhance this…
The B cell receptor (antibody on surface)
Together with a COMPLEMENT BINDING CORECEPTOR on surface
What inhibits signalling on surface of the B cell?
Fc receptor
Binding to Fc region of an antibody
How do T cells provide a costimulatory signal to tell B cells to produce antibodies?
They upregulate CD40 ligand
This engages with CD40 on B cell. Tells it to make antibodies.
Also T cell produces IL-4 and IL-5 which tell a B cell to make antibodies.
What receptors (ABs) do B cells express once matured but before class switching?
IgM and IgD receptors
Remember; class switching and somatic hypermutations improve antibody affinity and function
What are the only cells that can activate T helper cells?
Antigen presenting cells of class II MHC
What can T helper cells further be divided into?
Th1 and Th2
Big cytokine producers
What do Th1 cells stimulate?
Activate macrophages and cytotoxic T cells
Secrete cytokines such as IFNy (tells macrophages to kill a microbe)
What do Th2 cells do?
Provide costimulatory help to B cells
Secrete the cytokines IL-4 and IL-5
What cytokine promotes Th1 production but inhibits Th2?
IL-12
What cytokine promotes Th2 production but inhibits Th1?
IL-4
What is inhibition of development of Th1 or Th2 cells by cytokine IL-4 and IL-12 known as?
Reciprocal inhibition
What activates cytotoxic T cells ?
Antigen presenting cells of class I MHC
Usually present viral fragments
Can also be stimulated by T helper Th1 cells
What do T regulatory cells express? CD___ and CD___
CD4 and CD25
CD 25 also known as (IL-2Receptor.
What anti-inflammatory cytokines do T regulatory cells secrete?
IL-10, TGFbeta
Do T cell receptors undergo somatic hyper mutations?
No
They stay the same
With same low affinity for antigens
Do T cell receptors have high affinity or low affinity for antigens?
Low affinity
That’s why T cells have to be presents antigens by antigen presenting cells.
What are T cell receptors associated with on T cell surfaces?
CD3 signalling chains
What cells recognise class I MHCs?
CD8 cytotoxic T cells
Presented on virally infected cells
What cells recognise MHC class II?
CD4 T helper cells
Th1 and Th2
What aspects of antigens are T cells able to recognise ?
Only able to recognise small fragments of antigens that’s been broken up by APCs and presented to T cell on MHC complex (tray)
In contrast to B cells that can recognise epitopes of whole antigens that haven’t been broken up.
We react to antigens in different ways from individual to individual.
This is because we inherit ___ different genes coding for different ___ classes.
12 different genes
MHC classes
What 2 chains are MHC class I peptides made of? What about MHC class II?
Class I alpha 1 and alpha 2 chains
Class II alpha 1 and beta 1 chains
Which has a smaller antigen binding groove, class I or class II MHC?
Class I has a smaller class II has a larger
When an APC presents an antigen to a T cell, what does the TCR interact with?
Both the MHC protein and the antigenic peptide fragments.
It interacts with the MHC protein because this tells the t cell not to destroy the self cell.
How do T cells decide whether to be cytotoxic T cells or T helper cells?
In the thymus T cells mature and encounter a range of self antigens
Once they engage with an MHC it helps to determine what they will become
What is positive selection?
When undergoing Thymic selection and T cells are deciding whether they want to be T helpers or cytotoxic, if the T cell doesn’t encounter and bind and MHC the cell will be signalled to die as it has not recognised a self antigen.
What is Negative selection?
When T cells are undergoing Thymic selection, and a Tcell binds too strongly to self antigen and becomes activated, these T cells are signalled to die as they must be SELF REACTIVE T cells!!
What is peripheral tolerance?
TCR binding to an MHC bound to an antigen is not enough alone to activate T cell. You need costimulatory molecules to produce a second signal. This is the basis of why T cells don’t become activated in inappropriate situations.
What 2 molecules make up signal 2, the ACTIVATION signal?
CD 28 on T cell surface.
B7-2 on APC surface.
These bind forming signal 2
These are the main costimulatory molecules.
What 2 molecules make up the INHIBITORY SIGNAL of T cells , dampening the immune response?
CTLA-4 and B7-1
These switch off activation of T cell
Produced by T cell
What do naive T cells (mature T cells that haven’t yet encountered an ANTIGEN ) posses? CD__
CD28
Is type I diabetes mediated by destruction of pancreatic B cells by ANTIBODIES OR T CELLS?!!!
T CELLS!! NOT ANTIBODIES.
What’s HLA - B27 associated with?
Increased risk of ankylosing spondylitis
Chronic arthritis.
Majority of ppl with B-27 are healthy
