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IMED3001 > Body Defences: Hypersensitivity > Flashcards

Body Defences: Hypersensitivity Flashcards

1
Q

What are the types of hypersensitivity reactions?

A

Type I, II, III, IV

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2
Q

What is a hypersensitivity reaction?

A

Excessive or aberrant immune reactions that cause tissue injury and disease.

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3
Q

What causes hypersensitivity reactions?

A

Over reactivity to foreign antigens

Self reactivity

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4
Q

How are hypersensitivity reactions classified?

A

Type I: immediate

Type II: Anti-tissue antibodies

Type III: Immune complex

Type IV: T-cell mediated

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5
Q

What causes immediate hypersensity?

A

Pathological reaction caused by release of mediators from mast cells after reacting and binding to IgE.

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6
Q

What are IgE-mediated immediate hypersensitivity reactions called?

A

Allergies and atopy

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7
Q

What are the features of immediate hypersensitivity reactions?

A

Rapid reactions

Usually reactions to antigens that enter at epithelial surfaces (skin and mucosa of upper respiratory tract)

Involves allergens, allergen-specific IgE, and mast cells

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8
Q

What causes allergen-specific IgE production?

A

Activation of Th2 cells

Stimulated by IL-4 and IL-13 and inhibited by IFN-gamma

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9
Q

What affects the balance between stimulation and inhibition of Th2 response?

A

Route of administration of antigen

Chemical and physical characteristics of antigen.

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10
Q

What happens when allergens enter the body?

A

It is taken up and processed by APCs and Th2 cells are activated resulting in IgE response

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11
Q

How does IgE interact with mast cells?

A

It binds to mast cells via Fc(ε)

Cross-linking of 2 antibodies by antigen results in mast cell degranulation and release of mediators

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12
Q

What are contained within mast cell granules?

A

Histamine

Cytokines

Products of arachidonic acid such as leukotrienes

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13
Q

How can mast cell granules be released?

A

IgE dependent and independent reactions

Endogenous mediators such as tissue proteases and cationic proteins from eosinophils and neutrophils.

Chemicals such as toxins, venoms, and proteases

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14
Q

What are some inflammation mediating cytokines that are produced by mast cells?

A

Histamine

Tryptase

PAF/lipid nucleases

Nitric oxide

Endothelin

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15
Q

What chemicals are immediately released after signal for degranulation by mast cells?

A

Histamine

Eosinophil chemotactic factors

Heparin

Neutrophil chemotactic factors

Platelet activating factor

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16
Q

What chemicals are produced during degranulation and are released minutes later?

A

Leukotriens

Thromboxanes

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17
Q

What is produced hours after mast cell degranulation?

A

IL-3

IL-4

IL-5

IL-6

GM-CSF

This leads to immune responses hours after antigen exposure

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18
Q

How are cells involved in immediate hypersensitivity developed?

A

Initial antigen exposure -> Activation of Th2 and Tfh cells -> Tfh cells produce stimulatory cytokines (IL-4/IL-13) -> Production of allergen-specific IgE -> IgE binds high-affinity Fc receptors on mast cells -> subsequent re-exposure to allergen cross-links antibodies and activates mast cells -> Mast-cell mediators are secreted

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19
Q

What are possible consequences of mast cell degranulation?

A

Immediate and late stage responses

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20
Q

What does histamine do?

A

Dilates small blood vessels and increases vascular permeability.

Stimulates smooth muscle contraction (eg airways resulting in anaphylaxis)

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21
Q

What is a consequence of protease production?

A

May cause damage to local tissues

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22
Q

What is the product of release of arachidonic acid metabolites?

A

Vascular dilation

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23
Q

What is the consequence of leukotriene production?

A

Stimulate prolonged smooth muscle contraction.

24
Q

What do cytokines released by mast cells do?

A

They induce local inflammation in late stage reaction

25
Q

What is the overall result of mast cell degranulation?

A

Acute vascular and smooth muscle reactions and inflammation

26
Q

How is the morphology of tissue different in early and late phase responses?

A

immediate reaction -
vasodilation, congestion,
and edema.

The late-phase reaction -
inflammatory infiltrate rich
in eosinophils, neutrophils,
and T cells

27
Q

What causes increase mucus production and late phase chronic inflammation in Hay fever?

A

IL-13

28
Q

What does the gut do in response to histamine release?

A

Increased peristalsis resulting in vomiting and diarrhoea

29
Q

True or False: All cases of asthma are associated with IgE production.

A

False, some cases are but not all. All cases are caused by mast cell activation.

30
Q

What causes bronchial asthma?

A

Most often due to allergies.

Some are not associated with IgE (all are mast cell activation related)

May be triggered by cold or exercise

31
Q

What is anaphylaxis?

A

Most severe form of immediate hypersensitivity. Characterized by:

Oedema in many tissues (including larynx)

A fall in BP

Bronchoconstriction

32
Q

What causes anaphylaxis?

A

Widespread mast cell degranulation in response to systemic distribution of antigen and can be life threatening

33
Q

What are the most common triggers of anaphylaxis?

A

Bee stings

Penicillin-family antibiotics

Ingested nuts or shellfish

34
Q

How is immediate hypersensitivity treated?

A

Antihistamines

Bronchodilators

Adrenaline in anaphylaxis

Corticosteroids to inhibit inflammation

35
Q

What are the aims of immediate hypersensitivity therapy?

A

Inhibiting mast cell degranulation

Antagonizing effects of mast cell mediators

Reducing inflammation

36
Q

How is desensitization therapy administered?

A

Repeated small dose allergen administration

37
Q

How does desensitization work?

A

APCs activate regulatory T cells

Regulatory T cells release chemicals that suppress, change, or eliminate Th2 cells.

Reg T cells influence B- cells to produce antibodies that are not IgE and so they block IgE from binding.

IgE no longer triggers an immune response in these pathogens.

38
Q

How can anti-tissue antibodies cause damage to local tissues?

A

Inducing local inflammation. (leukocytes are recruited)

Inducing phagocytosis and destruction of cells (IgG1, and 3 bind to macrophage and neutrophil Fc receptors)

Interfering with normal cellular functions.

IgM can activate complement cascade

Leukocytes at sites of antibody deposition release ROS and lysosomal enzymes that damage tissue in area.

Antibodies can activate and inhibit receptor functions

39
Q

What condition is caused by antibody stimulating a receptor?

A

Graves disease (TSH receptor is stimulated)

40
Q

What condition is caused by inhibited receptor function?

A

Myasthenia gravis (AChR inhibited in neuromuscular junction by antibodies)

41
Q

What causes immune complex-mediated hypersensitivity?

A

Antibodies other than IgE form complexes that deposit in blood vessels and cause inflammation to surrounding tissues by attracting and activating leukocytes.

42
Q

Are immune complexes formed with non-self antigens only?

A

No immune complexes can be due to circulating antigens in the blood or microbial antigens (such as that in hepatitis)

43
Q

What kind of problems arise from immune complex formation?

A

Inflammation in blood vessels, joints, and organs.

IgG1, IgG3, and IgM can activate the classical complement pathway and can recruit leukocytes to induce cytokine release and inflammation.

44
Q

Examples of immune-complex mediated diseases:

A

Systemic lupus erythematosus

Polyarteritis nodosa

Poststreptococcal glomerulonephritis

Serum sickness

Arthus reaction

45
Q

How are anti-body mediated hypersensitivity conditions treated?

A

Drugs (Corticosteroids and immunosuppressants)

Plasmapheresis (reduce levels of circulating antibodies or immune complexes)

Intravenous IgG from health donors (unknown why this works but potentially due to competitive binding and eradication of problematic antibodies)

Depletion of B cells (using antiCD20 antibodies)

Antibodies that block CD40 or its ligand

Antibodies that block cytokines that promote B cell survival

46
Q

What is the aim of anti-body mediated hypersensitivity treatment?

A

Limit inflammation and damage

47
Q

What causes T-cell mediated hypersensitivity?

A

Autoimmunity (against cellular antigens with restricted tissue distribution)

Exaggerated or persistent responses to environmental antigens (Can be caused by contact sensitivity to drugs)

T cell responses to microbes (TB style granuloma formation making infection difficult to eradicate)

Excessive polyclonal T cell activation by microbial toxins due to superantigen actions (large amount of inflammatory cytokines resulting in condition similar to septic shock)

48
Q

What kind of cytokines are produced by Th1 and Th17?

A

Th1 (IFN-gamma) which activates macrophages

Th17 (recruits leukocytes including neutrophils)

49
Q

What causes tissue injury in T-cell mediated hypersensiticity?

A

Mainly due to activation of macrophages and neutrophils

50
Q

What causes delayed-type hypersensitivity?

A

T cell activation takes time and circulating T cells must be activated and then relocated to the peripheral tissue that is exposed to antigens.

51
Q

How does T-cell hypersensitivity cause damage to host?

A

CD4+ activation causes inflammation, macrophage activation, and neutrophil activation (Th1 and Th17 pathways)

CD8+ T cell activation specific for host cell antigens

CD8+ T cell cytokine production (not a major source of cytokines)

52
Q

What kind of disorders are T-cell mediated hypersensitivity disorders?

A

Organ-specific autoimmune disorders.

Disorders that are chronic and progressive and self-perpetuating

53
Q

What are chronic inflammatory diseases caused by immune reactions also called?

A

Immune-mediated inflammatory diseases

54
Q

What causes T-cell mediated hypersensitivity responses to self-tissues?

A

Damage to tissue results in release of altered self proteins which are “new” epitopes and so these proteins are responded to by activating immune system. Activating an immune response against these epitopes causes other self epitopes to become a trigger for immune response against many self antigens (due to similarity of damaged epitopes to self epitopes) creating autoimmune disease.

55
Q

What is epitope spreading?

A

Activating an immune response against damaged self epitopes causes other self epitopes to become a trigger for immune response

56
Q

How is T-cell mediated hypersensitivity treated?

A

Potent anti-inflammatory steroids

More targetted therapies based on fundamental mechanisms of disease. (eg TNF-alpha inhibitors in rheumatoid arthritis)

Newer agents developed to inhibit T cell responses

B-cell depletion with anti-CD20

IMED3001 (46 decks)

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