Hypersensitivity Flashcards
(28 cards)
give some common sources of allergens
- inhaled
- injected
inhaled materials
- plant pollens
- mold spores
- dander of domesticated animals
- faces of v small animals e.g. house dust mites
injected materials
- insect venoms
- vaccines
- drugs
give some common sources of allergens
- ingested
- contacted
ingested
- food e.g. peanuts
- orally administered drugs
contacted
- plant leaves e.g. poison ivy
- metals e.g. nickel
what are the 1st 2 types of hypersensitivity reactions?
type 1
- binding of antigen to IgE on mast cells
- release of inflammatory mediators
type 2
- small molecules that modify cell-surface components perceived as foreign by immune system
what are the type 3 and 4 hypersensitivity reactions?
type 3
- small soluble immune complexes
- small soluble molecules + IgG deposited in the walls of small blood vessels or alveoli of the lungs
type 4
- products of antigen-specific effector T-cells CD4 Th1 cells
Type 1:
what is the immune reactant?
what is the antigen?
what is the effector mechanism?
what are the examples of hypersensitivity reactions?
IgE
soluble antigen
mast-cell activation
allergic rhinitis
asthma
systemic anaphylaxis
Type 2:
what is the immune reactant?
what is the antigen?
what is the effector mechanism?
what are the examples of hypersensitivity reactions?
IgG
- cell- or matrix- associated antigen
OR 2. cell-surface receptor - complement, FcR+ cells
- antibody alters signalling
- some drug allergies e.g. penicillin
- chronic urticaria
type 3
what is the immune reactant?
what is the antigen?
what are the effector mechanisms?
what are the examples of hypersensitivity reactions?
IgG
soluble antigen
complement
phagocytes
serum sickness
arthus reaction
type 4
what are the immune reactants?
what are the antigens?
what are the effector mechanisms?
what are the examples of hypersensitivity reactions?
- Th1 cells
- Th2 cells
- CTL
1 + 2. soluble antigen
3. cell-associated antigen
- macrophage activation
- eosinophil activation
- cytotoxicity
1 + 3. contact dermatitis
2. chronic asthma or chronic allergic rhinitis
describe the process of type 1 hypersensitivity
- allergen binds and turns B cells into plasma cells that produce lots of IgE
- IgE binds to cells with IgE receptors on
= mast cells - mast cells filled with granules containing inflammatory mediators
- allergen cross-links with bound IgE on mast cell surface
- -> de-granulation of mast cell granules and release of inflammatory mediators
where are mast cells found?
mucosal and epithelial tissues
what is histamine?
what is its role?
toxic mediator in mast cell granules
toxic to parasites
increases vascular permeability
causes smooth muscle contraction
what are Leukotrienes C4 and D4?
what is their function?
what drug can inhibit them?
lipid mediators in mast cell granules
inflammation
smooth muscle contraction
increased vascular permeability
mucus secretion
aspirin
(anti-inflammatory)
where are histamine receptors?
H1 endothelial cells
smooth muscle cells
how do you prevent and treat allergic reactions?
prevent:
avoiding contact with the allergen
treatment: drugs - antihistamines, corticosteroids immunological - desensitisation
describe how desensitisation works
monoclonal antibody binds to IgE
describe how desensitisation works
monoclonal antibody binds to IgE
-> prevents IgE binding to receptor on mast cell
(works the same for Fc)
why do we have type 1 hypersensitivity?
how does it do this?
part of immune system specialised to fight worm infection
gastrointestinal tract:
increases peristalsis and muscle contractions
increased fluid secretion
-> expulsion via vomit or diarrhoea
airways:
decreases diameter
produces more mucous
-> expulsion via phlegm or coughing
blood vessels:
increased blood flow
increased permeability
-> increased lymph flow and carriage of antigen to lymph nodes
give an example of types of worms which can still effect people today
Guinea worm
- drinking water contaminated by larvae
Toxocara canis
- from dog faeces
what do Helminth infections stimulate?
CD4 Th2-like receptors
-> raised levels of IgE + increased no.s of eosinophils
also:
- down regulates Th1 immune responses
- protects against allergies
what is the Th1-Th2 balance?
what are their different roles?
the balance between different T helper cells
Th1
- activation of macrophages, cytotoxic T cells, NK cells
- elimination of cellular antigens (viruses, intracellular bacteria, tumour cells)
Th2
- stimulation of B cells
- boost in the synthesis of IgE, IgG1 and IgG3 antibodies
what happens if the Th1-Th2 balance is unbalanced?
more Th1
= immune response
-> can lead to autoimmunity
more Th2
= allergic response
how do helminth infections effect the Th1-Th2 balance?
induce strong Th2 responses
but also protect against allergy
what inhibitory responses can Helminth infections have?
blood circulation
pancreas
lungs
CNS
how do helminths suppress autoimmunity and allergy?
via type 2 or regulatory immune response
different immunomodulatory molecules (IMs) activate immune cells that promote responses
