Clinical Immunology (16-27) Flashcards
How can NK cells subsets be identified?
identified by expression levels of CD56
- CD56 bright are cytokine producing
- CD56 dim are cytotoxic
- a third subset lacking CD56 has recently been discovered
How do NK cells deal with infection?
- killing via perforin/granzyme system
–> important for antiviral and antitumour response - produce cytokines such as IFN-gamma to modulate immune responses
How are NK cells activated?
- NK cells are constantly exposed to activation and inhibition signals
- binding to self MHC inhibits them from being activated
- When self MHC is missing, NK cells usually enter an activated state and release immune mediators or cytotoxic granules to kill their target
Is missing self MHC alone enough to induce activation?
no, as all blood cells would be lysed
lacking MHC does not activate an NK cell, it simply reduces the activation threshold needed to activate them
other stress molecules such as cytokines activate NK cell
When would cells be missing MHC class I?
- certain viruses can downregulate MHC class I to prevent antigen presentation
- tumour cells reach equilibrium where their formation rate is the same as their rate of removal by the immune system
- once tumour cells downregulate MHC class I, it allows the tumour to escape the immune response and become malignant
How do NK cells synergise w the T cell response?
NK cells are able to target infected cells that the T cell would not be able to recognise
NK cells can be activated much easier than CD8 T cells
- do not require antigen presentation in order to activate
How do NK cells mediate antibody dependent cellular toxicity?
The Fc receptor, FC-gamma-RIII (CD16) on NK cells recognise antibodies bound to target antigen
crosslinking causes NK cell to release intracellular stores of perforin and granzymes
perforin punctures holes in cell membrane allowing granzyme to enter target cells and induce apoptosis
What are primary immunodeficiencies (PID)?
genetic immune deficiencies
disorders in which part of the immune system is either eliminated or functioning abnormally
leads to increased heightened susceptibility to infection by particular classes of pathogens
different to AID (AIDS), which is a result of external infection or disease treatment
What are some genetic characteristics of PIDs?
most single gene PIDs are recessive
ie one good gene compensates for a faulty one, more common if parent are genetically related
majority of PIDs are X-linked recessive
- where generally only males show symptoms eg IPEX, X-linked SCID
- X inactivation would preferentially inactivate chromosome with the mutation in the sense that cells that carry the good chromosome are allowed to progress
often complete loss not compatible with life, so mutation may produce gene product w partial function-hypomorphic
How can susceptibility to certain types of pathogens give a clue to type of PID?
CD4 T cells enhance innate immune responses and types of opportunist infections can gve a clue to type of PID since different types specialise against different ones
eg increased susceptibility to extracellular bacteria may mean a deficiency in Th17
What opportunistic infections correlate with what immune cell deficiencies?
- intracellular bacteria
- macrophage or T cell defect - extracellular encapsulated bacteria
- defect in antibody, complement, phagocytes or Th17 - fungal
- T cell dysfunction - recurrent herpes viruses
- NK and CTL deficiency
- viral susceptibility might lead to cancer
When to think of PID as a diagnosis?
- recurrent infections
- opportunistic pathogens
- normally mild infection becomes life threatening
- persistent high WBC counts
- persistent low WBC counts
If PID is suspected, as an immunologist what would be the next steps?
- haemoglobin levels
- total and differential WBC count
- platelet count
- analysis of lymphocyte subsets for numbers of T, B, and NK cells
- microbiology on organisms isolated
- check antibodies made to commonly used vaccinations
- request tests for severe combined immunodeficiency (SCID)
–> infants w SCID have undetectable or v low levels of T cell receptor excision circles
–> if VDJ recombination does not happen = not T cells as this is required for maturation
How can B cell function be evaluated in an individual in vitro?
induced antibody production in response to pokeweed mitogen
How can T cell function be evaluated in an individual in vitro?
proliferation in response to phytohemagglutinin or to tetanus toxoid
How can phagocyte function be evaluated in an individual in vitro?
phagocytosis of colourless nitroblue tetrazolium will turn phagocyte blue due to release of ROS
if this does not occur then their is a deficiency in the ability of the phagocyte to kill pathogens
used to test for chronic granulomatous disease
What are the treatment options for those with PIDs?
- treat symptoms
PIDs need antimicrobial therapy to clear and prevent infection - replace what is missing
a) antibody replacement therapy
eg Intravenous Immunoglobulin (IVIG)
IgG antibodies to many different pathogens administered evert 3-4 weeks
after that IgG could be given subcutaneously by self administration
b) complement similarly replace using donor material
What are long term treatments for PID?
a) replace
stem cell therapy and/or gene therapy
b) activate
phagocytes can be activated w injections of IFN-gamma
c) stimulate proliferation
if neutrophils not produced in normal numbers, granulocyte colony-stimulating factor (G-CSF) raises levels of white cells including granulocytes
What is the most common type of SCID and how can it be cured?
a mutation in the common gamma chain (CD132) on T cells prevents IL-2 signalling, inhibiting T cell proliferation
activation of B cells does not happen as there are not T cells to induce isotype switching
–> can only produce IgM
–> looking at levels of antibodies is important
can be cured w a bone marrow transplant
results are less satisfactory if the patient has active infections at the time
In what situation is gene therapy used to treat PIDs?
allowed only if
- no bone marrow match is available OR the patient is too ill to have transplant
AND
- patient has life-threatening infection unresponsive to conventional treatment, including steroid
What is agammaglobulinaemia?
a type of PID that results in no Igs
due to Bruton tyrosine kinase (BTK) mutation
–> crucial role in B cell development
stop codon found by gene sequencing due to deletion of 4 bps
–> frame shift
–> no mature B lymphocytes
associated w failure of Ig heavy gene rearrangement
What is the role of BTK in B cell maturation?
signalling insufficient without BTK to induce differentiation into mature peripheral B cells
- BTK overexpression in B cells get uncontrolled Ab production and systemic lupus erythmatosus (SLE)-like disease
–> effective BTK inhibitor is ibrutinib
What is chronic granulomatous disease (CDG)
phagocytes require NADPH oxidase (PHOX) to digest bacteria they have taken up
–> respiratory burst is critical for killing bacteria
defects in any one of four essential subunits of PHOX can cause CDG of varying severity
formation of granulomas due to phagocytes not being able to kill pathogens they have taken up
How can CDG be treated?
- continuous antibiotic therapy to help prevent antibacterial infections
–> infections usually require additional antibiotics - corticosteroid drugs for treating granulomatous complications
- IFN gamma
- bone marrow transplants have proven to be successful in some cases
If you have a case study where listeria is present what area of the immune system should you suspect?
complement
What is Type I hypersensitivity?
IgE- mediated
immediate
How are IgE’s produced and how do they induce an immune response?
Th2 cells produce IL-4 which induces B cell class switching to IgE
v low level in serum
bound to Fc-epsilon-1 receptors on mast cells
- antigen crosslinking induces degranulation
–> v few IgE molecules needed
- usually antibodies can only bind receptor if it has antigen bound, IgE is an exception
What are the two different types of granules in a mast cell?
- preformed granules
immediate release - synthesised after activation
delayed release
What molecules are contained in a mast cell?
Cytokines
- IL-3 signals eosinophils to arrive at site and IL-5 promotes degranulation, releasing major basic protein
- IL-4 activates Th2 cells, and more IgE production
- proteolytic enzymes activate components of complement
- histamine promotes smooth muscle contraction in the gut
What is the result of intravenous entry of allergen?
IgE mast cells receive systemic delivery of antigen resulting in widespread release of histamine which acts on blood vessels to increase permeability
- leads to hives at low doses (>mg)
- in higher amounts, can lead to anaphylactic shock (mg-g)
What is the result of subcutaneous entry of allergen?
causes wheal and flare reaction in skin
wheal: local inflammation
flare: redness around wheal due to vasodilation
What is the result of entry of allergen through inhalation?
nhalation causing exposure in upper respiratory tract leads to increased mucous production and nasal irritation
asthma in the lower respiratory tract causes contraction of bronchial smooth muscle
where the allergen gets into the airway is dependent on the size of it as well as the concentration
What is the result of entry of allergen through ingestion?
ingestion causes contraction of intestinal smooth muscle, causing vomiting
flow of fluid into the gut causes diarrhoea
- anaphylaxis
What is anaphylactic shock?
induced by food: 5-120 minutes
skin eg insect bite: 5-30 minutes
serious allergic reactions such as narrowing of airways, vomiting, sudden blood pressure drop
needs urgent treatment
What are the risk genes?
- genes associated with increasing Th2 or Th17 responses
- FceR polymorphisms
- reduced skin barrier function
it is the RISK of allergy that is inherited, not the specific allergy
How can allergens be determined?
testing can be done by a skin prick test, where potential allergens are put underneath the skin
How can allergy be treated?
- avoidance
- antihistamines
–> blocks specific histamine receptors - beta2-andrenergic agonists
–> preventing smooth bronchial muscle contraction in asthma - epinephrine (adrenaline)
stimulates both alpha and beta adrenergic receptors, decreases vascular permeability, so increases blood pressure, and reverses airway obstruction
–> epipen
What are two strategies for allergen immunotherapy and desensitasation?
- inducing Treg production by increasing dose of antigen through subcutaneous injection
- secrete IL-10
- reduces Th2 activity
- reduces IL-4
- reduces IgE secretion
- specific IgG secretion increases - allergenic dose of allergen delivered orally as mouth contains few mast cells
- no allergy symptoms
- induce Tregs
- secrete IL-10
- reduces Th2 activity
- reduces IL-4
- reduces IgE secretion
- specific IgG secretion increases
- eventually leads to reduced allergy symptoms, even when exposed to allergen eg pollen in nose
What is Type II hypersensitivity?
other antibody types binding to cell surface antigens
often RBCs
–> immune-mediated haemolysis by activation of complement and/or antibodies opsonize cell
eg penicillin allergy
–> binds to RBC surface, if antibodies react to penicillin they will bind and induce macrophage uptake
What is Type III hypersensitivity?
Immune complex (IC) mediated
–> lattices of antigen and antibody
consequence of IgG binding antigen to form an immune complex
eg farmers lung, antibodies against mould spores cause inflammation in the lungs
What is Type IV hypersensitivity?
a delayed response, mediated by T cells
–> cellular hypersensitivity
eg T1 diabetes: T cells destroying beta cells in pancreas which produce insulin
What is Type V hypersensitivity?
antibody mediated that are specific for cell surface receptors like type II
–> the difference is the response is stimulatory instead of destructive
eg Grave’s disease
What is Graves’ disease?
Type V hypersensitivity
overactive production of thyroxin
–> antibodies stimulate TSH receptor without presence of hormone, which leads to production of thyroid hormones, but the negative feedback loop does not work as autoantibodies are still being made
–> heat intolerance
–> anxiety
–> bulging eyes
Why was there a delay in tumour immunotherapy?
due to genetic origins, the immune system was thought not to be involved
What was the experiment that first showed that cancer is an immunological disease as well as a genetic one?
both immunodeficient and immunocompetent mice where injected with carcinogens
after 200 days, it was seen that there was a higher percentage of immunodeficient mice with tumours compared to immunocompetent
How can tumour immunoediting result in malignant tumours?
- cancer cells downregulate MHC-I
- changing antigens to avoid T cell response
- upregulating non-specific antigen onto MHC to avoid immune response
- can recruit immune cells such as Tregs and M2 macrophages that secrete TGF-beta and IL-10 to dampen immune response
–> macrophage can promote angiogenesis
How can monoclonal antibodies be used to target the tumour directly?
block growth factor receptors
eg trastuzumab, binds to HER2
–> improves median survival in breast cancer patients
–> This blockade inhibits HER2-mediated signaling cascades that promote cell proliferation, survival, and angiogenesis
eg rituximba binds CD20, blocking B cell activation
–> treats rheumatoid arthritis and B cell lymphoma
deplete tumour cells expressing tumour associated antignens
eg CD38
How can monoclonal antibodies be used to target the tumour immune response?
block checkpoint inhibitors
eg CTLA-4
BiTEs used to enhance T cell function
