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Flashcards in Autoimmune hypersensitivity Deck (14):

Type I / IgE mediated hypersensitivity

Allergic or anaphylactic
IgE antibodies typically bind to Rcepsilon receptors on mast cells and basophils.
Mast cells typically found in mucosal surfaces and skin. If you meet the allergen it binds to IgE on the mast cells, cross links them and this signals the mast cells to degranulate which effectively means release a bunch of pharmacoactive substances from the granules in its cytoplasm
The related molecules in the granules:
- Some attract neutrophils etc to the site of release
- Some are activators that effect vasodilatation and activate compliment platelets
Other effects: complement, platelets, spasmogens, smooth muscle contraction, mucus secretion.


Type II / IgG mediated

When you are making antibodies against some of our tissue associated antigens
ADCC cells have receptors for Fc portion of Ig molecules and lyse target cells when cross linked
This can activate complement
which can damage tissue, and deposits C3b which can form aside for neutrophil attachment


Type III / IgG immune complex mediated

example = chronic infection, antigens diminish over time as innate and adaptive immune systems deal with the infection , but if infection persists you may have antigen present for longer, and this antigen may be present when we are starting to make appreciable antibodies to this antigen, you can get immune complex induced vasculitis and nephritis, complexes that form will be large lattice like structures rather than smaller complexes
Large immune complexes:
- stick to capillaries and lodge in small vessels
- many Fc regions that neutrophils can attach to which can lead to removal of the antigens and pathological consequences e.g. occlusion of micro thrombus formation, complement formation can lead to membrane attack by neutrophils


Type IV / TH cell mediated

DTH (delayed type) involves CD4 T cells
e.g. Tb and the mantoux test is checking for specific CD4


Rhinitis common causes

House dust mite
Animal dander


Insect sting common causes?

Proteins in venom
Anaphylaxis common


Food allergies common causes

Wheat protein
Milk proteins


small molecules - common causes

penicillin, codeine, morphine


respiratory tract - common sites and types of allergies

allergic rhinitis (hay fever)
Sinusitis (inflamed nasal sinuses)
asthma (with allergic component)


Presentation of allergy on the skin

Urticaria (weals)
Angioedema (deeper skin involvement)


Gut presentation of allergy

diarrhoea, abdo cramps, vom


Multiple organs presentation of allergy

Anaphylaxis (medical emergency)


Allergy treatment

Avoidance - often difficult e.g. hay fever
Antihistamines - common for mild forms e.g. hay fever
Corticosteroids - essential for chronic conditions e.g. asthma
Sodium cromoglycate - stabilises mast cells
Sympathomimetics - epinephrine (adrenaline) in anaphylaxis
Desensitisation - gradually reducing dosses of allergen to induce high affinity IgG antibodies (complete with IgE for allergen)


Haemolytic disease of the newborn
- an example of type II hypersensitivity

RhD- mum becomes prog with RhD+ babe
the pregnancy is fine, but when the baby is born there is some mixing with the baby's red cells of the mothers circulation, mother starts to make antibodies to the RhD molecules, initially IgM then IgG the latter is transported across the placenta.
First babe born fine, but has sensitised the mother to produce anti Rh antibodies, if she subsequently becomes positive with an Rh feteus, anti RhD antibodies will be transported across the placenta and lead to complement mediated lysis of babes red cell and haemolytic disease
This was initially treated by intrauterine transfusions, but nowadays is treated by stopping development of antibodies in the first place, because immediately after the birth of the first babe you inject the mother passively with anti-RhD antibodies, to neutralise and remove any of the babes red cells that might have gotten into her circulation. so that if she becomes prog again there wont be antibody to hurt babe but if has another RhD plus kid will need another injection