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Microbiology and Immunology > Hypersensitivity reactions (asthma and allergy) > Flashcards

Hypersensitivity reactions (asthma and allergy) Flashcards

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1
Q

What are the 4 types of hypersensitivty?

A

Type 1 - immediate hypersensitivity
Type 2 - cytotoxic hypersensitivity
Type 3 - serum sickness and arthus reaction
Type 4 - delayed type hypersensitivty / contact dermatitis

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2
Q

What is hypersensitivty?

A

Innappropriate immune respponse to non-infectious antigens that results in tissue damage and disease

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3
Q

Give a few example of type 1 hypersensitivity?

A

Allergy
Astha
Anaphylaxis

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4
Q

What is the immune reactant and the antigen for type 1 hypersensitivity (allergy)?

A

IgE is the immune reactant

Allergen/soluble antigen with IgE binding epitopes is the antigen

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5
Q

What is the effector mechanism for type 1 hypersensitivity?

A

Mast cell activation due to IgE which cross link to activate mast cells which cause degranulation

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6
Q

How are mast cells activated?

A

They have specific IgE on surface and if antigen present and it binds, mast cells cross link to become activated

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7
Q

What happens once mast cells are activated?

A

Causes vasodilation and increased capillary permeability causing wheel and flare reaction

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8
Q

What is the wheel and flare individually?

A

Wheel - tissue swelling from inflammation and oedema

Flare - around the wheel caused by vasodilation

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9
Q

Give an example of wheel and flare reaction?

A

Mosquito bite and allergy tests (purpoefully induce response using allergen)

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10
Q

When does systematic anaphylaxis take place?

A

Some people when exposed to allergen , rapdi swelling of tissues on face may cause occlusion of resp tract

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11
Q

How id systematic anaphylaxis treated and why?

A

Immedaitely since occlusion to resp tract is deadly and must use adrenaline (epi-pen)

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12
Q

What are type 2 hypersensitivty reactions (cytotoxic hypersensitivity) caused by?

A

Altered components of human cells e.g. drugs attached to blood cells such as penicillin

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13
Q

What is the immune reactant and the antigen in cytotoxic hypersensitivity (type 2)?

A

IgG (anti-drug antibodies) are the immune reactant

Drug that has coated cell is the antigen

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14
Q

What is the effector mechanism for cytotoxic hypersensitivity?

A

Antibody bound cells are cleared by macrophages and complement

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15
Q

What is a side effect of hypersensitivity to penicillin?

A

Haemolytic anameia - red blood cells with penicillin attached to it are cleared

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16
Q

What else might IgG antibodies target in type 2 hypersensitivity apart from drugs?

A

Own cell surface receptors causing uncontrollable activation or block the receptor’s function

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17
Q

What is an example of IgG overstimulating a receptor (TYPE 2 HYPERSENSITIVITY)?

A

Grave’s disease

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18
Q

What is an example of IgG blocking a receptor (TYPE 2 HYPERSENSITIVITY)?

A

Myasethenia Gravis

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19
Q

How does IgG cause graves disease?

A

Antibody generated targets TSH receptor (thyroid stimulating hormone) causin excess stimulation of thyroid so excess thyroxine is produce without from normal feedback loop

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20
Q

How does IgG cause myasethenia gravis?

A

Antibody binds to neuromuscular junction and blocka neurone impulses so ACh c ant stimulate muscle leading to paralysis (drooping eyelid)

Antibody not only block ACh but can also destroy ACh leading to same thing

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21
Q

Which type of hypersensitivity results in haemolytic disease in newborn?

A

Type 2 hypersensitivity - death in uterus from haemolytic anameia

22
Q

Why does haemolytic anaemia happen inside the uterus to the foetus?

A

Mother rhesus negative blood group antigen which has positive. During birth as placenta separates from uterus, foetal blood cells can be exposed to mother who produces antibodies to it. If in next pregnancy, foeuts is rehsus positive, mothers antibodies attack destroy red blood cells = haemolytic anaemia

23
Q

What is the immune reactant and antigen of type 3 hypersensitivity 9serum sickness/arthurs reaction)?

A

IgG is the immune reactant and soluble antigen

24
Q

What is the effector mechanism of type 3 Hypersensitivty?

A

IgG and soluble antigen forms immune complexes which are cleared by phagocytes. Immune complexes also activate complement resulting in immune activation and inflammation

25
Q

Where does arthus reaction take place?

A

Localised e.g. after vaccination

26
Q

What are the steps causing arthus reaction?

A

Mast cells activated from immune complex. Mast cell release inflammatory mediators.

Inflammatory cells invade site and blood veseel permeability and blood flow is increased.

Platelts also accumulate leading to occlusion of small blood vessels causing heamorrhage leading to appearnance of purpura

27
Q

What is purpura?

A

Purple coloured spots on skin and mucus membrane

28
Q

What causes serum sickness?

A

Large intravenous doses of soluble antigen e.g. antivenom. Too many IgG antibodies produced so they form immune complexes with antigen.

29
Q

What happens in serum sickness after immune complexes are formed?

A

Immune complexes are deposited in tissues e.g. blood vessel walls and complement activation causes tissue damage resulting in inflammatory process

30
Q

What is farmer’s lung?

A

Inflammation in lung due to immune reaction in alveoli after mould inhaled into lungs eventually resulting in fibrosos and permanent damage after repeated episodes

Not just mould, can be sugar cane dust, cotton, hay etc…

31
Q

What is hypersensitivity peumonitis?

A

Farmer’s lung but with any particel inhaled e.g. protein from pigeons in pigeon breeder’s lung

32
Q

What is the histology of lung of someone with hypersensitivity peumonitis?

A

Intersititial pneuomonitis
Non ceasating granulomas - causes long term damage to lungs
Intersititial fibrosis

33
Q

What are the 3 differnet routes of delivery + examples of each causing type 3 hypersensitivity?

A

Inhaled e.g. farmer’s lung
Subcutaneous - arthus reaction
Intravenous high dose - Serum sickness

But all inflammation is localised

34
Q

Which cells cause delyaed type hypersensitviity (Type 5)?

A

Th1 e.g CD4, sometimes Th2

35
Q

What is the immune reatcant and the antigen in delayed type hypersensitivity?

A

Th1 and Th2 specific to antigen

Soluble antigen

36
Q

What are the effector mechanisms of Th1 and Th2 in delayed type hypersensitivity?

A

Th1 activated once contacted by antigen on macrophages (presenting antigne from second round) and produce interferons and cytokines - reaction

Th2 cells activated due to antigen on eosinophils and releases proteins, enzymes and cytokines in response

37
Q

Give an example of Th1 mediated and Th2 mediated delayed type hypersensitivity?

A

Tuberculin reaction by Th1

Allergic contact dermatitis e.g. nickel - by Th2

38
Q

What is a manoux test?

A

Inject ppd in, if previously exosed to TB, strong Th1 immune response will show via lesion size

39
Q

What are the steps in delayed hypersensitivity due to Th1 cells? (manoux test)

A

Antigen is injected into subcutaneous tissue which is process by local antigen presenting cells.

Th1 effector cell recongises the antigen and releases cytokines to act on vascular endothelium

Recruitment of phagocytes and plasma to site of antigne injection causes visible lesion

40
Q

How far does delayed type hypersensitivity dpread?

A

Localised - only to where antigen is

41
Q

What are the steps in Th2 mediated contact dermaitities?

A

Antigen enters skin, APC picks up and present which Th2 recognise from prev encounter and releases cytokines causing reaction seen as dermatitis e.g. poison ivy

42
Q

What is allergy?

A

Disease following a response by the immune system to an otherwise innocuous antigen

43
Q

How do diff allergies differ?

A

Site of allergy though all need IgE e.g. pollen diff from food allergy due to place

44
Q

What is IgE a defense against?

A

First line defense against paraisitic worms, now instead against innocuous antigens

45
Q

What does IgE bind to?

A

FceR1 receptor on mast cells or also eosinophils

46
Q

How is IgE produced?

A
47
Q

What causes allergen sensitisation?

A
48
Q

Name a few common allergens?

A
49
Q

How do some allergens lead to tolerance?

A

High dose exposure

50
Q

What types of molecules can be allergeneic?

A

Microbiology and Immunology (31 decks)

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