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Flashcards in 29. Hypersensitivity types Deck (35):
1

Hypersensivity reaction types

1. Anaphylactic and atopic (type I)
2.Cytotoxic ( antibody mediated, type II)
3. Immune complex (type III)
4. Deleayed ( cell mediated , type IV)

2

Anaphylactic and atopic (type I ) hypersensvity reaction - mechanism

Antigen induce the formation of IgE through Th2 and IL-4 ---> Reexposure --> Freee antigen cross- links IgE on presenting mast cells and basophils , triggering immediate re release of vasoaactive amines that act at postcapillary venules ( eg. Histamine). Rapidly reaction because of preforemed antibody --> delayed production of arachidonic acid metabolites (e.g Leukotrienes) --> neutrophils and eosinophils

3

Anaphylactic and atopic (type I) hyperreaction - main vasoactive amine and where it acts

Histamine --> post capillary venules

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anaphylactic and atopic (type I) hypersensivity reaction - test

skin test for specific IgE

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Type I hypersesnsivity -reaxtion - delayed respond -cell

Neutrophils and eosinophils

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Basophil contains

1. heparin ( densly basophilic granules)
2. histamine (densly basophilic granules)
3. synthesis and release leukotriene

7

Mast cell releases

1. Histamine
2. Tryptase
3. eosinophil chemotactic factor
4. Heparin

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Eosinophil produce

1. Histaminase
2. Major basic protein ( a helminthotoxic)

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Cytotoxic (antibody mediated ) Hypersensivity reaction- mechanism

IgM, IgG bind to fixed antigen on " enemy " cell --> complement activation --> membrane attack complex (MAC) --> a. opsonization and phagocytosis b. complement and Fc-mediated inflammation c. antibody - mediated cellular dysfunction

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Cytotoxic (antibody mediated ) Hypersensivity reaction- disease tends to be specific on

tissue or site where antigen is found

11

Direct Coombs test - definition and example

detects antibodies that have adhered to patient RBCs eg test an Rh+ infant of an Rh- mother

12

Indirect Coombs

detects serum antibodies that can adhere to othweR BCs eg test in Rh- woman for Rh+ antibodies

13

Cytotoxic (antibody mediated ) Hypersensivity reaction- types of antibodies

IgM
IgG

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Immune Complex Hypersensivity reaction- mechanism

Antigen - antibody (IgG) complexes --> activate complement --> attracts neutrophils which release lysosomal enzymes

15

Type II reaction associated with

1. Vasculityis
2. Systemic manifestation

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Serum sickness mechanism

Antibodies formation to foreign proteins (take 5 days) --> immune compexes formation and deposition in membranes --> fix the complement --> tissue damage

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MC serum sickness is caused by

drugs (not serum) acting as haptens

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Haptens are

Small molecules that elicit an immune response only when attached to a large carrier ( eg. protein ) which may be one that also does not elicit an immune response by itself

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Serum sickness - antibodies formation takes ... (time

5 days

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Serum sickenss - sx

1. Fever
2. Urticaria
3Arthralgia
4. Proteinuria
5. Lymphadenopathy
6. Splenomegaly
7. Eosinophilia
OCCURS 5-10 days After antigen exposure

21

Arthurs reaction mechanism

local subacute antibody - mediated hypersensivity reaction --> intradermal (or subcutaneous) injections into a pre-sensitized (has circulating IgG individual leads to immune complex formation in the skin --> activation of complement --> PMN infiltration and platelet clumbing

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Arthus reaction - time

3-6 h

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Arthus reaction - sx

edema and necrosis

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Arthus reaction vs serum sickness according to time and whic is mc

Arthus reaction --> 3-6 H MC
Serum sickness --> 5days

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Arthus reaction - diagnosis

immunofluorescent staining

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Arthus reaction - example

tetanus immunization if they are are given at same site with too short interval between immunization (min interval usually 5 years)

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Delayed (cell mediated ) Hypersensivity reaction (IV) - mechanism

sensitized T cells encounter antigen and then release cytokene (leads to macrophages activation ) DOES NOT INVOLVE ANTIBODIES (I, II, III)

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Hypersensivity rection type II is cell mediated so it is not transferable by

serum

29

HSR IV - test

1. patch test
2. PPD

30

• What are the 4 Ts associated with type IV hypersensitivity reactions? How is it tested for?

T-lymphocyte mediation, Transplant rejection, TB skin tests, and Touching (contact dermatitis); with patch test, PPD (for TB)

31

How does the mnemonic ACID help you remember important features of the four types of hypersensitivity reactions?


Type I = Anaphylactic and Atopic, type II = Cytotoxic, type III = Immune complex, type IV = Delayed

32

A man has fever, joint pain, enlarged lymph nodes, hives, and proteinuria. He started a new drug 7 days ago. What type of reaction is this?

Serum sickness (type III hypersensitivity reaction

33

Which type of hypersensitivity reaction does the Coombs test look for? Describe the difference between a direct and indirect Coombs test.

Type II; direct = detects antibodies that are already stuck to RBCs, indirect = detects antibodies that can stick to RBCs

34

• A mother is Rh- and her infant may be Rh+. Whom do you test with the indirect Coombs test? Whom do you test with the direct Coombs test?

Test the Rh- mother for Rh+ antibodies with the indirect Coombs; test the Rh+ infant for antibodies adhered to RBCs with the direct Coombs

35

A patient suffers from a type II hypersensitivity reaction. The complement system is activated. How does it destroy the patient's cells?

Antibody and complement lead to formation of the membrane attack complex (MAC) (type II is cy-2-toxic)