Autoimmune hypersensitivity Flashcards
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
cytotoxic
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
Pollens
Animal dander
Insect sting common causes?
Proteins in venom
Anaphylaxis common
Food allergies common causes
Wheat protein
Milk proteins
Peanuts
Strawberries
small molecules - common causes
penicillin, codeine, morphine
respiratory tract - common sites and types of allergies
allergic rhinitis (hay fever)
Sinusitis (inflamed nasal sinuses)
Conjunctivitis
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
