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Dermatology > Hypersensitivity reactions > Flashcards

Hypersensitivity reactions Flashcards

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Dermatology Board Prep flashcards
1
Q

Define hypersensitivity

A

exaggerated or inappropriate immune response against a foreign of self antigen

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2
Q

What are the 4 types of hypersensitivity reactions?

A

type 1 = allergic
type 2 = cytotoxic
type 3 = immune complex
type 4 = delayed

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3
Q

What diseases are associated with type 1 hypersensitivity?

A

allergic rhinitis
asthma
atopic dermatitis
anaphylaxis

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4
Q

What diseases are associated with type 2 hypersensitivity?

A

AIHA
myasthenia gravis
Goodpasture’s disease
graft rejection

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5
Q

What diseases are associated with type 3 hypersensitivity?

A

serum sickness
Lupus nephritis
Arthus reaction

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6
Q

What diseases are associated with type 4 hypersensitivity?

A

contact dermatitis
tuberculosis

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7
Q

Mediators of type 1 hypersensitivity reactions

A

antigen/IgE cross-linking on mast cells and basophils

Th2 cells
histamine

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8
Q

Mediators of type 2 hypersensitivity reactions

A

tissue-bound IgG/IgM activates complement or effector cells

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9
Q

Mediators of type 3 hypersensitivity reactions

A

formation of antigen-IgG immune complexes

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10
Q

Mediators of type 4 hypersensitivity reactions

A

memory T cells (not by antibodies like others)

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11
Q

What are the key phases of type 1 hypersensitivity reaction?

A

sensitisation = IgE produced in response to allergen, IgE binds FcR on mast cells/basophils, occurs on first exposure (would not notice this reaction)

activation = re-exposure to allergen, allergen cross-links IgE causing immediate degranulation

causes tissue damage:
- vascular permeability
- mucus secretion
- immune cell infiltration

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12
Q

Define asthma

A

immediate bronchospasm due to mast cell-released spasmogens

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13
Q

What are the potentially fatal consequences of anaphylaxis?

A

laryngeal oedema
bronchial constriction
peripheral oedema

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14
Q

Signs and symptoms of anaphylaxis

A

swelling of conjunctiva
runny nose
swelling of lips, tongue and/or throat
fast/slow HR
low BP
gives, itchiness, flushing
pelvic pain
loss of bladder control
crampy abdominal pain
diarrhoea, vomiting
SOB
wheeze/stridor
hoarseness
cough
lightheadedness
loss of consciousness
confusion
headache
anxiety

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15
Q

Tests for type 1 hypersensitivity

A

skin prick test
blood test (serum IgE levels)
test diet or food challenge (patient placed on diet free from most allergens, foods added over time)

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16
Q

Type 1 hypersensitivity treatments

A

allergen avoidance
desensitisation (repeated injection of small but increasing doses of purified allergen over several months –> modification of Th2 response to increase IgG)
Drugs:
- antihistamines
- corticosteroids
- leukotriene receptor antagonists
- sodium cromoglicate (blocks Ca influx into mast cells)
- salbutamol
- monoclonal IgE (Omalizumab)
- adrenaline

17
Q

What is the hygiene hypothesis?

A

limiting early life infection impeded natural immune system development and causes predisposition to allergic disease

18
Q

Describe type 2 hypersensitivity reactions

A

directed against cell surface or extracellular matrix antigens
most common type 2 reactions involve RBCs
activation via IgG or IgM

19
Q

How is an antigenic target lyses in type 2 hypersensitivity reactions?

A

ADCC (antibody dependent cellular cytotoxicity)
- Ig binding via FcR of NK cells, neutrophils or macrophages (effector cells)
- release of cytotoxic enzymes

Direct complement lysis
- classical pathway

20
Q

What happens as ABO-incompatible donor cells enter the blood stream?

A

they are lysed
intravascular haemolysis via complement-mediated lysis
leads to renal failure and death
prevent by cross-matching patient serum with donor RBC
blood typing by haemagglutination

21
Q

What causes haemolytic disease of the newborn (rhesus disease)?

A

rhesus antigens expressed on RBC surface
problems occur in pregnancy after sensitisation (not first baby)

RhD +ve fetus in RhD -ve mother
postpartum sensitisation = anti-RhD antibodies produced
subsequent pregnancy = haemolysis, anti-RhD antibodies attack RhD antigens of fetus causing lysis of RBCs

22
Q

How can drugs induce haemolytic anaemia?

A

drug/metabolite binds to surface protein on RBC
antibody binds to drug and activates complement
complement causes haemolysis

23
Q

What causes autoimmunity?

A

IgG directed against self-antigens on tissues

24
Q

Describe type 3 hypersensitivity reactions

A

similar to type 2 but antibodies directed against soluble antigens leading to formation of immune complexes

damage caused by deposition and build up of complexes in tissues or walls of small blood vessels

25
Q

Which conditions can cause granulomatous type 4 hypersensitivity?

A

TB
Leprosy
Leishmaniasis
Schistosomiasis

26
Q

What is the most clinically-important form of type 4 hypersensitivity?

A

granulomatous type 4 hypersensitivity
- develops after 21-28 days
- antigen persistence causing chronic T cell and macrophage activation leading to granuloma formation

Dermatology (23 decks)

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