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IMMUNO > 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

What is the name of Type 1 hypersensitivity?

A

Immediate hypersensitivity / anaphylactic hypersensitivity

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4
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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5
Q

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

A

IgE antibodies

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6
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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7
Q

Which cells does IgE bind to?

A

Mast cells and basophils

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8
Q

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

A

Fc epsilon receptor 1

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9
Q

what happens if an allergen encounters cell bound IgE?

A

Rapid cross linking and degranulation of the mast cell

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10
Q

What is released when the mast cell degranulates?

A

Histamine

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11
Q

What affect does histamine have?

A

Promotes further Th2 differentiation and highly active smooth muscle contracting molecules like leukotrienes

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12
Q

What is the name of Type 2 hypersensitivity?

A

antibody mediated cytotoxic hypersensitivity

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13
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

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14
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
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15
Q

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

A
  1. Anti-receptor activity
  2. Antibody dependant cell mediated cytotoxicity
  3. Classical activation of the complement cascade - formation of membrane attack complexes which results in a destruction of the cells osmotic integrity and
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16
Q

What happens in type 3 hypersensitivity?

A

When immune complexes are not cleared - leads to an inflammatory response and the attraction of leukocytes

17
Q

What is an immune complex?

A

A soluble antigen bound to antibody

18
Q

What is the difference between complement activation in type 2 and type 3 hypersensitivty?

A

Type 2 results in small amounts of proteins generated, large amounts in type 3

19
Q

What affect do C3 and C4 have in type 3 hypersensitivity?

A

They act as chemokines by attracting neutrophils to the side

20
Q

What do neutrophils do when they arrive at the immune complex in type 3 hypersensitivity?

A

They degranulate and result in tissue necrosis and vasculitis

21
Q

Describe serum sickness?

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

22
Q

Why is the degranulation of neutrophils so toxic to cells?

A

They degranulate and release oxygen radicals

23
Q

What is a membrane attack complex?

A

When fragments of the complement system come together, they form a MAC which attaches to the cell surface membrane and this creates a channel that allows fluid to pass in and out the cell

24
Q

What is a membrane attack complex?

A

When fragments of the complement system come together, they form a MAC which attaches to the cell surface membrane and this creates a channel that allows fluid to pass in and out the cell which disturbs the osmotic integrity of the cell = lysis

25
Q

How does antibody independent 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

26
Q

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

A

T cells

27
Q

Using poison ivy as an exmaple describe how type 4 hypersensitivity reactions occur?

A
  1. Skin touches poison ivy
  2. Antigens through epidermis and picked up by dendritic cells - they become antigen presenting
  3. Taken to lymph nodes, antigen presented to T cells, using MHC II
  4. T cell binds to MHC on DC using TCR and CD4 as well as CD28 which binds to B on DC
  5. DC releases cytokines which trigger the T helper cell to differentiate into Th1 effector
  6. Releases IFN-gamma which activates macrophages that release pro-inflammatory cytokines
28
Q

What do active macrophages release?

A

Pro-inflammatory cytokines like TNF, IL-1 and IL-6

29
Q

What cytokine does the DC release which allow the naive T cell to differentiate?

A

CD12

30
Q

Which Interleukin has an autocrine effect?

A

IL-2

31
Q

What does IL-2 do?

A

Has an autocrine effect, allows for t cell proliferation

32
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

33
Q

In which auto-immune disease do patients develop IgGs against DNA or proteins present in the nucleus (nucleoproteins) forming persistent immune complex deposits and a variety of pathologies?

A

Systemic lupus erythematosus

34
Q

What symptoms can immune complexes not being efficiently cleared lead to?

A

Symptoms such as fever, rashes, joint pain or protein in the urine

35
Q

Why do immune complexes not initiate complement cascade?

A

The classical pathway activation results in formation of membrane attack complex which occurs in cell wall

Whereas immune complexes are free-floating

36
Q

What needs to occur before T cells can initiate type IV?

A

Sensitisation phase where antigen is presented to naive T cells by antigen presenting dendritic cells → results in the generation of antigen specific memory T cells

IMMUNO (14 decks)

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