Hypersensitivity reactions I Flashcards

1
Q

what is a hypersensitivity reaction

A

Exaggerated or inappropriate immune response to an antigen/immunogen, causing tissue damage (involves both innate and adaptive immune responses)

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2
Q

2 examples of a Type I (Immediate) hypersensitivity reaction, involving Ig E antibody

A

Hay fever
Allergic asthma
hives
food allergies

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3
Q

what antibodies do Type II (Cytotoxic) reactions involved e.g transfusion reactions

A

IgG, IgM antibodies

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4
Q

what is type III hypersensivity reaction, involving IgG, IgM antibodies known as

A

complex mediated

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5
Q

an example of Type IV (Delayed) reaction, involving T lymphocytes and macrophages

A

Contact dermatitis (eczema)

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6
Q

When does a type I hypersensitivity reaction occur

A

immediately after contact with an immunogen/allergen

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7
Q

what antibody is produced in a type I hypersensitivity reaction by plasma cells

A

IgE

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8
Q

what response do parasites cause

A

they trigger an TH2 response where B cells produce parasite-specific IgE and so an inflammatory response so parasites get ejected from human host

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9
Q

what does IgE bind to on the surface of mast cells and basophils to release inflammation mediators (asthma, hay fever)

A

Fc receptors

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10
Q

allergen

A

an immunogen which causes an allergy eg
* pollen
* animal dander
* house dust mite faeces
* food allergens : nuts; shellfish, eggs
* bee and wasp venom

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11
Q

Allergenicity

A

the ability of an antigen to induce the abnormal immune response (Th2 mediated)

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12
Q

Atopy

A

the genetic predisposition to produce IgE

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13
Q

what are normal serum IgE levels

A

0.1-0.4

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14
Q

how many types of IgE receptors are there which differ in IgE affinity

A

2

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15
Q

whats the low affinity IgE receptor known as

A

CD23

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16
Q

what cells is the high affinity IGE receptor (FceRI) expressed on

A

mast cells and basophils (also some eosinophils, platelets and monocytes)

17
Q

how many polypeptide chains does High affinity receptor IgE FceRI have

A

4 polypeptide chains:
▪ alpha, beta and 2 identical gamma chains
OR
alpha, and 2 gamma chains (on monocytes and platelets)

18
Q

what are Mice lacking FceRI alpha chain resistant to

A

anaphylaxis (reaction)

19
Q

what is the Key cell in the orchestration of the inflammatory response

20
Q

where is mast cell found

A

skin, connective tissues, and mucosal epithelial tissue of respiratory, digestive and genitourinary tract.

21
Q

what receptors do mast cells express on their surface

A

high-affinity IgE receptors

22
Q

what do cytoplasmic granules in mast cells contain which are repsonsible for many signs of allergic reactions

A

preformed mediators (Histamine, Heparin, Chymase, Tryptase)

Membrane-derived mediators (Leukotrienes; prostaglandins)

23
Q

what initiates mast cell degranulation

A

IgE cross linkage, anaphylatoxins (C3a, C5a) and drugs

24
Q

what protein gets activated when there’s IgE receptor cross-linkage, leading to phosphorylation reactions and generation of second
messengers

A

Activates protein tyrosine kinase (Lyn)

25
what mineral is involved when there is IgE cross-linkage and how
calcium theres an uptake of extracellular calcium and a release of intracellular calcium stores
26
what acid is formed when phospholipase A2 enzyme is activated in IgE receptor cross linkage
arachidonic acid (inflammation)
27
type I hypersensitivity reaction sequence of events (6)
1. allergen absorbed through the mucosa 2. APC presents the processed allergen 3. B cells produce specific IgE (t cells help) 4. allergen-specific IgE binds to mast cells via Fc receptors 5. Re-exposure (allergen cross-links surface-bound IgE) 6. Mast cell degranulates
28
3 consequences of a type I hypersensitivity reaction
anaphylatic shock food allergies hay fever allergic asthma
29
whats anaphylactic shock usually caused by
systemic release of mast cell mediators
30
where do airborne allergens triggers mast cell degranulation in hay fever
the nasal mucosa
31
what happens in allergic asthma un the lower respiratory tract
◼ Bronchial hyperreactivity ◼ Inflammatory infiltrate into the mucosa and submucosa ◼ Epithelial layer denudation/damage ◼ Goblet cell hyperplasia and excessive mucus secretion ◼ oedema (excess water fluid) ◼ bronchoconstriction