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IMMUNO my version > Hypersensitivity > Flashcards

Hypersensitivity Flashcards

1
Q

What is an antigen?

A

An antigen is a molecule which can be recognised by an antibody or the adaptive immune system

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2
Q

What is meant by hypersensitivity?

A

Refers to the undesirable reactions produced by the immune system, including autoimmunity and allergies

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3
Q

give some examples of allergens that can cause type 1 reactions

A

foods (e.g. peanuts), plants (e.g. timothy grass, birch trees), animal dander (e.g. cats, dogs), drugs (e.g. penicillin, sulphonamides) and insect products (e.g. bee venom, house dust mites).

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4
Q

What is the name of Type 1 hypersensitivity?

A

Immediate hypersensitivity / anaphylactic hypersensitivity

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5
Q

What is type 1 hypersensitivity triggered by?

A

The re-exposure to a specific antigen which is referred to as an allergen

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6
Q

What type of antibodies are type 1 hypersensitivity reactions mediated by?

A

IgE antibodies

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7
Q

Which cytokines promote the B cell to class switch into an IgE producing cell?

A

IL-4 and IL-13

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8
Q

Which cells does IgE bind to?

A

Mast cells and basophils

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9
Q

What receptor do IgE use to bind to the mast cells?

A

Fc epsilon receptor 1

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10
Q

what happens if an allergen encounters cell bound IgE?

A

Rapid cross linking and degranulation of the mast cell

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11
Q

What is released when the mast cell degranulates?

A

Histamine, a host of cytokines that can recruit other cells and promote further Th2 differentiation, and highly active smooth muscle contracting molecules such as leukotrienes and prostaglandins.

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12
Q

what are leukotrienes?

A

highly active smooth muscle contracting molecules

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13
Q

What affect does histamine have?

A

it is a vasodilator

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14
Q

how can you diagnose allergies?

A

using a skin prick test (wheal and flare)

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15
Q

which reactions create the wheal and flare reaction?

A

Type 1, seen in the skin prick test

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16
Q

What is a multivalent antigen?

A

Antigen that has multiple sites at which an antibody can attach or antigen can be produced

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17
Q

What factors influence the initial sensitisation of the immune response to allergens?

A

Genetics, age, the environment

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18
Q

How do allergies happen immunologically?

A

First, the body must be sensitised to the allergen.
When the allergen initially enters the body, it results in generation of Th2 cells and Tfh cytokines IL-4 and 13.

When these act on B cells the cells switch to producing allergen (antigen) specific IgE.

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19
Q

when do non-allergic people produce IgE?

A

only against potent venoms or parasitic infections

20
Q

What is the name of Type 2 hypersensitivity?

A

antibody mediated cytotoxic hypersensitivity

21
Q

what are the 3 phases in type 1 hypersensitivity reactions?

A
  1. early Phase
  2. Later Phase
  3. Late Phase
22
Q

when does the early phase occur?

A

few mins following exposure to allergen

23
Q

when does the later phase occur?

A

within a few hours of exposure to allergen caused by the recruitment of early inflammatory cells such as neutrophils.

24
Q

when does the late phase occur?

A

3-4 days after exposure where high frequencies of eosinophils are recruited and Th2 cells are present.

25
Q

What does type 2 hypersensitivity involve?

A

The destruction of cells by IgG or IgM antibodies that are bound to antigens present on the surface of cells - normally healthy cells

26
Q

What are examples of type 2 hypersensitivity reactions?

A
  1. Graves disease - antibodies bind to thyrotrophin receptor resulting in the over production of thyroid hormones
  2. Haemolytic disease of newborns - maternal antibodies can cross the placenta and destroy fetal red blood cells
  3. Immune thrombocytopenia - antibodies develop gainst platelets
27
Q

What are the three mechanisms by which Type 2 hypersensitivity reactions can occur?

A
  1. Anti-receptor activity - blocking or activating its function
  2. Antibody dependant cell mediated cytotoxicity
  3. Classical activation of the complement cascade
28
Q

how does the Classical activation of the complement cascade lead to cell death?

A

antibodies on the surface of cells is recognised by the complement components, ultimately leading to the formation of the membrane attack complex (MAC) in the surface of the cell, and cell death due to loss of osmotic integrity.

29
Q

what are the effects does type 2 hypersensitivity lead to?

A
  • tissue injury including local or systemic inflammation,
  • cell depletion leading to a loss of function or imbalance in organ function.
30
Q

What happens in type 3 hypersensitivity?

A

When immune complexes are not cleared. The immune complexes end up being deposited in the blood vessel walls and tissues, promoting inflammation and tissue damage

31
Q

what are the symptoms of type 3 hypersensitivity?

A

fever, rashes, joint pain or protein in the urine:

32
Q

What happens in systemic lupus erythematosus (SLE)?

A

Patients develop IgGs against DNA or proteins present in nucleus of cells (nucleoproteins) which form persistent immune-complex deposits and a variety of pathologies

33
Q

which kind of diseases typically causes type 3 hypersensitivity?

A

autoimmune conditions

34
Q

What is an immune complex?

A

non-cell bound antigen-antibody complexes

35
Q

Using snake venom as an example, explain how serum sickness arises?

A

When a patient is biten by a snake, the venom of the snake enters into the blood stream
Patient is given anti-venom, which the patient produces antibodies against
Therefore during the second bite, immune complexes may be formed

36
Q

how does type 4 hypersensitivity arise?

A
  • Sensitisation phase occurs where antigen is presented to naive T cells by antigen presenting dendritic cells, resulting in generation of antigen specific memory T cells- takes several weeks
  • On subsequent exposure these memory T cells respond promoting inflammation at site of exposure
37
Q

what is the other name for type 4 hypersensitivity reactions?

A

(delayed) T-cell mediated hypersensitivity

38
Q

why is there a delay between exposure and response in type 4 reactions? how long is this lag?

A

because the memory T cell response (which requires recruitment and expansion) is slightly slower than antibody mediated memory
peak responses are seen 2-3 days following re-exposure

39
Q

How does antibody dependent cell-mediated Cytotoxicity work?

A

When a NK cell binds to the immune complex by recognising the Fc tail
Releases perforin which allows for the entry of granzymes and granulysin - results in cell death in an apoptotic way

40
Q

What are the primary cells involved in Type 4 Hypersensitivity reactions?

A

T cells

41
Q

Name the cytokines released when in contact with poison ivy?

A

IFN- gamma

42
Q

Explain how contact dermatitis occurs?

A
  • skin is exposed to poison ivy
  • here a small molecule urushiol acts as a hapten (and binds to proteins in skin), driving T helper 1 response
  • On re-exposure these memory cells produce cytokines such as IFN-gamma which promote the pro-inflammatory activation of macrophages resulting in swelling and oedema
43
Q

what are the intracellular pathogens that can cause type 4?

A

measles virus and Mycobacterium tuberculosis

44
Q

The test for what infection is conducted via the means of a type 4 hypersensitivity reaction?

A

tuberculosis - positive test = raised bump due to oedema / tissue swelling initiated by pro-inflammatory cytokines

45
Q

Are type 4 reactions only limited to Th1 cells?

A

No, any T memory cell can cause type 4 reactions

46
Q

Can one disease initiate multiple different types of hypersensitivity reactions?

A

Yes! in many diseases more than one type of hypersensitivity reaction may be contributing to pathology at the same times.

IMMUNO my version (14 decks)

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