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Flashcards in Immunity Deck (42)
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Describe how co-stimulation is used

When TCRs bind to their specific MHC (usually class 2), a signal is produced which causes CD28 (found on T cells) to bind to B7-2 (found on APCs)


This upregulates CTLA-4 and B7-1, which downregulates any further immune response


Explain Fc mediated effects

The Fc region is the bottom part of the antibody


Its effects will change dependent on what type of receptor/cell it binds to, as well as the type of immunuglobulin that is present (eg, A,D,G....)


Eg, when bound to a mast cell, degranulation occurs....releasing histamine

Whilst binding to a neutrophil will cause phagocytosis of the attatched microbe/pathogen


What are inactivated vaccines?

These are not alive and cannot replicate, so cannot form a disease state....even in the immunocompromised


Produced by culturing the virus/bacteria in a media, and then inactivation by heat/chemicals


This can be expensive, and people can have hypersensitivities to them


What are the 4 types of hypersensitivity reactions?

I - Immediate Hypersensitivity (allergy)


II - Autoantibodies


III - Deposition of immune complexes


IV - T cell mediated tissue injury


How are B cells and T cells activated?

The B cell presents the T cell with an antigen (which it has taken from a chopped up pathogen)


CD40, from the B cell, then binds to its receptor on the T cell, activating the T cell


T cell activation causes cytokines to be released, which bind to the original B cell --> causing them to proliferate


Why does our immune response struggle with tumours?

As they are mainly 'self' cells, and so are seen as weakly immunogenic


There are also few specific oncoproteins or self-antigens that are easy to target (normally hidden)


These are normally targeted by Cytotoxic T cells and NK cells


What are Somatic Hypermutations?

These are beneficial mutations that occur in amino acid chains, making antibodies more specific, and so better


Explain how blood grouping works

Everybody has a basic glycolipid antigen (O)


Some people have attatched carbohydrate groups (A or B)


These groups produce antibodies against the other types of blood (eg, A produces anti B antibodies)


How are Conjugate Polysaccharide vaccines made?

The surface polysaccharide from the pathogen is grown (via fermentation) and isolated


The carrier protein is also grown and purified seperately


Toxins are then removed from the polysaccharide, before being covalently bonded to the carrier protein


Purification and formulation then occurs


Describe Type 1 hypersensitivity reactions

Immediate Hypersensitivity


This is the stimulation of mast cells via the binding of FcR to IgE specifically


This causes increased vascular permeability, vasodialation, smooth muscle contraction and local inflammation


This occurs rapidly after antigen exposure


What are the first type of cells that respond to an infection?



Describe Type II hypersensitivties

Autoantibodies --> Occurs by 3 possible mechanisms


Activates complement and stimulate phagocytosis (eg, haemolytic anaemia)


Recruit neutrophiles, which can cause cell damage (eg, glomerular nephritis)


Can bind to receptors, which can stimulate or inhibit certain functions (eg, graves disease or myasthenia gravis)


What are live (attenuated) vaccines?

These are a weakend version of the real virus/bacteria


These must grow to a sufficient level inside the body to trigger the immune response


These are cheap and dont need adjuvants


But it can sometimes cause a disease to occur!!


How are live (attenuated) vaccines made?

The pathogen is passaged many times (eg, in chick embryo eggs) under stress conditions which causes the pathogen to have slower replication, and to lose its virulence factors


Purification and formulation then occurs


How can B cell activation be downregulated?

By the engagement of an Fc co-receptor


This occurs by antibodies returning to its parent B cell, binding to its Fc receptor


This switches off the B cell proliferation


What is the concept of vaccinology?

Being exposed to a pathogen that does not lead to a disease state


But memory cells still being produced


What are the 2 forms of T cells?

Helper T Cells (CD4+) - Recongnise fragments on class 2 MHC

Th1 - Activate macrophages and cytotoxic T cells (IFN/TNF)

Th2 - Provides co-stimulatory help to B cells, helping activating them (eg, IL-4/5/10)



Cytotoxic T Cells (CD8+) - Recognise fragments on class 1 MHC --> This kills the infected cells, and so is best for viral infections




What is a recombinant sub-unit vaccine?

Recombinantly (using other microbes) made vaccines that are made up of one antigenic part of the pathogen, such as proteins or surface polysaccharides




Explain how Antigen Recognition occurs?

T Cell recognise small fragments of antigens that are presented by APCs


Peptide fragments bind to the grooves of the MHC


The TCR binds to the MHC and peptide residues


CD4/8 (dependent on the class of MHC can also bind the MHC, preventing the death of the TCR


What is a vaccine adjuvant?


And what are the 4 reasons for having them?

They enhance the protection provided by vaccines by promoting rapid, long lasting and broad immunity


Stronger and longer immunity


Antigen-Sparing --> as less antigens are needed to form an immune response


Cross-reactive immunity --> induces a broader immune response


To overcome weakened immunity --> eg immunocompromised


What are the physical barriers of the innate immune system?

Epithelial cells


Can secrete defensins, which act as broad-spectrum antibiotics


The secretion of these is increased by the secretion/presence of cytokines


What are the 2 types of thymic selection?

Positive Selection - When the T cell doesnt recognise/bind to our test MHCs, so it signalled to die (via apoptosis)


Negative Selection - The T cell binds too strongly to the test MHC (activating it) and so is signalled to die (via apoptosis)


Explain the differences between the 2 classes of Major Histamine Complexes (MHC)?

Class 1 - These are recognised by CD8+ cells (cytotoxic T cells)

Present on all cells, so define what our 'self is' --> important for transplant patients



Class 2 - Recognised by CD4+ cells (helper T cells)


Only found on antigen presenting cells, like macrophages




When does Autoimmunity occur?

When there is a faliure/breakdown in mechanisms that are normally responsible for maintaining self tolerance


What are the 5 classes of antibody/immunoglobulin?

A --> Airborne


E --> Allergy

G --> General

M --> Immature



Describe Type III hypersensitivities

Deposition of immune complexes


This is the cross-linking of antibodies, which can cause several responses --> Can block blood vessels as they're so large


Normally causes complement activation and FcR -- neutrophil reponses


When systemic = Systemic Lupus Erythematosus (SLE)



What are Conjugate Polysaccharide vaccines?

Polysaccharides from the bacteria are attatched to a carrier protein (which are often toxoids)


This is because the polysaccharide itself will not illict a T-cell immune reponse


They have high efficacy and safety


What are the 5 different types of vaccine?

Live (attenuated)




Recombinant sub-unit




Conjugate polysaccharide-protein


Can T cell receptors undergo somatic hypermutation?



So their affinity remains at a constant low level


What are the 3 vital functions that a good immune system has?

It has quick recognition


Pathogens can be neutralised quickly


A good memory can be produced