Flashcards in Hypersensitivty Deck (37)
what is hypersensitivity?
exaggerated inappropriate adaptive immune response
what is sometimes a result of hypersensitvity?
inflammatory reactions and tissue damage result
when does hypersensitivity manifest?
not manifest on 1st contact with Ag usually appears on subsequent contact
how many types of hypersensitivity are there?
4 -Type I, II, III and IV
what types are antibody mediated?
Types I,II, III
what type is mediated by T cells and macrophages?
what immunoglobulin is involved in Type I hypersensitivity?
what is type I hypersensitivity ?
IgE response to innocuous environmental antigens i.e pollen, house-dust mites, latex, some drugs(local anaesthetics)
what does IgE bind to?
IgE binds to FcRI on mast cells
what occurs at the second encounter in type I?
Second encounter with allergen triggers release
of inflammatory mediators and produces acute inflammatory reaction within minutes with symptoms such as athasma and rhinitis
what inflammatory mediators are released in type I ?
Release of histamine, prostaglandins,
leukotrienes and other mediators of allergic response
what are 4 treatments for mild type I hypersensitivity?
2. Sodium chrooglycate
what is an example of a severe type I reaction?
what are symptoms of anaphylactic shock?
wheeze, swelling of face
nausea, dizziness, fainting,
low blood pressure
how is anaphylactic shock treated?
with adrenaline immediately
What is type II hypersensitivity ?
Antibody-dependent cytotoxic hypersensitivity
how long after exposure does type II hypersensitivity occur?
occurs in 12-18 hours of exposure to antigen
when does type II hypersensitivity occur?
when IgG or IgM binds to either a self-antigen or a foreign antigen on cells
what is a result of type II?
Phagocytosis, killer cell activity or complement-
mediated lysis (Damage is restricted to particular cells/tissues bearing the antigen)
Name example of type II reactions.
1. Blood transfusion reactions when ABO incompatible blood is transferred (fever, nausea,vomiting)
2. Haemolytic disease of the newborn
Describe the type II reaction of haemolytic disease of the newborn.
- Results from incompatibility of Rhesus D blood antigens to RhD-negative mother
- RhD-positive RBC from 1st foetus sensitise mother usually at birth
-If subsequent foetus is RhD-positive, anti-Rh IgG produced by mother crosses the placenta and attacks foetus
- RhD-negative mothers infused with anti-RhD IgG
immediately after delivery - eliminates all RhD-positive RBC before immune response occurs
what caused a reduction in child mortality from haemolytic disease?
when does type III hypersensitivity occur?
18-24 hours after exposure
what is an example of type III?
extrinsic allergic alveoli's
what is type III hypersensitivity mediated by?
persistence and deposition of
antibody-antigen immune complexes
What are immune complexes influenced by?
1. Route of Ag exposure eg poor clearance in lung
2. Dose of Ag
3. Size of IC (larger IC fall out of circulation)
4. Binding of Ag directly to tissues
what happens when the immune complexes are deposited?
cause severe inflammation
when does type IV hypersensitivity occur?
48-72 hours post Ag exposure
what are the 3 types of type IV hypersensitivity?
-contact- 48-72 hours
-tuberculin - 48-72 hours
- granulomatous - 21-28 days