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Immunology > Hypersensitivity reactions I > Flashcards

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

A

mast cell

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
Q

what mineral is involved when there is IgE cross-linkage and how

A

calcium

theres an uptake of extracellular calcium and a release of intracellular calcium stores

26
Q

what acid is formed when phospholipase A2 enzyme is activated in IgE receptor cross linkage

A

arachidonic acid (inflammation)

27
Q

type I hypersensitivity reaction sequence of events (6)

A
  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
Q

3 consequences of a type I hypersensitivity reaction

A

anaphylatic shock

food allergies

hay fever

allergic asthma

29
Q

whats anaphylactic shock usually caused by

A

systemic release of mast cell mediators

30
Q

where do airborne allergens triggers mast cell degranulation in hay fever

A

the nasal mucosa

31
Q

what happens in allergic asthma un the lower respiratory tract

A

◼ 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

Immunology (13 decks)

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