Immediate hypersensitivity

Question 1

why do some individuals preferentially make IgE antibodies>

Answer 1

• reason is unclear
• genetic component
• mode of administration of antigen (skin or mucous mem favor IgE)
• APC preferentially actiave TH2 cells resulting in the production of IL4 and IL3
• failure of control of TH2 cells

Question 2

activation of TH2 cells in IgE production

Answer 2

• APC presents and B7 binds to CD28
• IL2 is produced and interacts with IL2 receptor
• TH2 proliferates making more TH2
• TH2 cells release IL3 and 4 which interact with B cells causing release of IgE

Question 3

what does an IgE do

Answer 3

• binds to mast cells via the Fc receptor
• when antigen binds, it causes the mast cell to degranulate
• acute release of granules cause allergic rhinitis (hay fever)

Question 4

early phase mediators released by mast cells and basophils

Answer 4

• histamine
• protease
• leukotriennes
• prostaglandins
• platelet activating factor
• chemotactic factors for neutrophils and eosinophils

Question 5

late phase mediators released in the laste phase of the acute allergic response

Answer 5

• these are cytokines released from mast cells, TH2, macrophages, and eosinophils
• this phase can be controlled by corticosteroids that inhibit cytokine production

Question 6

examples of IgE mediated allergic reaction

Answer 6

• hay fever, allergic rhinitis
• bronchial asthma - bronchial constriction
• acute drug reactions
• food allergy
• insect stings
• acute urticaria (hives)

Question 7

diagnosis of acute allergic diseases

Answer 7

• skin prick tests (intradermal), positive will flare in 5-10 mins
• measure specific IgE antibodies to an antigen, this is often the RAST test

Question 8

treatment of type 1 allergic reactions

Answer 8

• epi used to treat acute anaphylactic reactions
• remove the antigen
• treat symptomatically with antihistamines, anti-leukotrienes, corticosteroids
• omalizumab (monoclonal antibody that inhibits IgE binding to mast cells)
• hyposensitization therapy (shots)

Question 9

hyposensitization (desensitization)

• what do you do
• what happens
• why does it happen

Answer 9

• consists of multiple exposures to increasing concentrations of the antigen.
• results in an increase of IgG antibodies
• if untreated, the body eracts with low IgG and high IgE
• after a while the IgG will pass the IgE and the IgE will go down
• could activate the Th1 cells or activate TREG cells to inhibit Th2 cells

Question 10

what other mechanisms can degranulate mast cells other than IgE?

Answer 10

• C5a and C3a (anaphylatoxins)
• heat
• cold
• pressure
• exercise
• CNA effects via the vagus nerve
• direct effect of drugs on mast cells