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Immunity and infection > Disorders of the immune system > Flashcards

Disorders of the immune system Flashcards

1
Q

What is a hypersensitivity reaction?

A

An exaggerated or inappropriate immune response that results in tissue damage

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2
Q

How many types of hypersensitivity reactions are there?

A

4 types: I, II, III, IV

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3
Q

What is type I hypersensitivity?

A

When allergic response is provoked by re-exposure to an antigen (allergen)

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4
Q

What are the two stages of a type I hypersensitivity reaction?

A

1) Sensitisation phase

2) Effector phase

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5
Q

What is the sensitisation phase?

A

B cells recognise pollen antigens and bind to them and internalise them
The B cells present antigens to Th2 cells
Th2 cells secrete IL-4
IL-4 causes B cells to switch class and become IgE producing cells
IgE circulates around body and comes into contact with mast cells
Fc portion of IgE binds to mast cells and now mast cells can recognise the pollen
Mast cells are now sensitised

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6
Q

What is the effector phase?

A

This is one second exposure of allergen
Mast cells bind to antigens
Leads to immediate phase reaction involving release of vasodilator amines such as histamine
Mast cells generate cytokines
Encourages Thelper cells to produce cytokines
Allergic reaction is prolonged
Muscle spasm, oedema, inflammation, leukocyte recruitment

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7
Q

Example of IgE mediated allergic disease (type I)

A

Asthma

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8
Q

What is a type II hypersensitivity reaction?

A

Antibodies bind to host cell antigens on cell surfaces
mediated by antibody-antigen interaction.
Antibodies are IgG or IgM

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9
Q

Examples of type II hypersensitivity reactions

A

Myasthenia gravis
Rhesus isoimmunisation
Grave’s disease

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10
Q

What happens in myasthenia gravis?

A

Body produces antibodies against nicotinic Act receptors = receptors get blocked
Motor neurones can no longer cause the muscle to contract or there is weak muscle contraction

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11
Q

What happens in rhesus isoimmunisation?

A

RhD is an antigen carried on RBCs
If mother RhD- gets pregnant with RhD+, mother can produce IgM against the antigen
IgM is too big to cross placenta, so baby not harmed
If mother gets pregnant again with RhD+ baby, memory B cells are stimulated and IgG is produced which can cross placenta and cause lysis of foetal blood

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12
Q

What happens in Grave’s disease?

A

Autoimmune thyroid disease
Characterised by low TSH and TRH, high thyroid hormones (hyperthyroidism)
-In grave’s disease, body produces autoantibodies to TSH receptor on thyroid gland
-Stimulates the receptor = release of thyroid hormones + hypertrophy of thyroid gland
-Negative feedback = low TSH and TRH

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13
Q

What is type III hypersensitivity reaction?

A

When antibodies target soluble circulating antigens

Can target self (e.g. lupus) or foreign (e.g. impetigo)

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14
Q

What happens in lupus?

A

Patients make autoantibodies against several self molecules (e.g. DNA)
As a result attack own cells
Can recruit complement to attack own cells
Leads to injury and inflammation
Immune complexes deposited in kidney glomerulus = glomerulonephritis

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15
Q

What can be seen in patients with lupus?

A
  • Abnormal B cell activation
  • B cells more sensitive to stimulatory cytokines
  • B cells can polyclonal activate
  • Changes in cytokine levels
  • Changes in T cell functions, decline in Th1 response
  • Phagocytic cells do not function properly
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16
Q

Type IV hypersensitivity reaction

A
  • Aka delayed (takes a few days to develop) hypersensitivity

- T cell mediated but dendritic cells, macrophages and cytokines also contribute to disease process

17
Q

What is the Mantoux test?

A
  • This is an example of type IV hypersensitivity reaction
  • Patient is injected with extract of mycobacterial antigen under skin
  • Macrophages present antigens with MHC class II to CD4+ cells
  • Specific Th cells get activated and release cytokines that activate macrophage and cause release of cytokines
  • Results in firm red swelling of skin
18
Q

What type hypersensitivity reaction is Type 1 diabetes an example of?

A
  • Type IV
  • Beta cells act as auto antigen
  • APCs engulf these and present peptides complexed with MHC II
  • These stimulate CD4+ T cells = release cytokines= activate cytotoxic T lymphocytes
  • Damage beta cells and insulin cannot be produced
19
Q

What type hypersensitivity reaction is Coeliac disease a result of?

A
  • Type IV
  • Patients have IGA antibodies against components of gluten (gliadin) and host cell proteins (reticulin, endomysial)
  • Antibodies released for intestine and there is inflammation, resulting in damage to intestinal mucosa = villous atrophy and malabsorption
20
Q

Why are ulcerative colitis and Crohn’s disease thought to be type IV hypersensitivity reactions?

A
  • There is change in proportion of T and B cells
  • Large number of B cells in intestinal mucosa produce autoantibodies
  • There is also complement deposition in the intestinal mucosal
  • Ulcerative colitis is Th2 mediated and Crohn’s Th1 mediated
21
Q

Why is psoriasis thought to be a type IV hypersensitivity reaction?

A
  • High number of CD4+ cells seen in skin

- Immunosuppressant treatments are effective

22
Q

What is autoimmunity?

A

Autoimmunity is an acquired immune reaction to self antigens

Autoimmune disease occurs when autoimmunity leads to tissue damage

23
Q

What are the causes of autoimmunity?

A
  • Age and gender
  • Genetics
  • Infection
  • Specific auto antigens
  • Drugs
  • Immunodeficiency
24
Q

Primary immunodeficiency

A

Due to problems with complements, phagocytes, humeral immunity or cellular immunity

25
Q

What is severe combined immunodeficiency syndrome

A

Lack of development of bone marrow stem cells into B and T cells

26
Q

What is hyper IgM syndrome

A

B cell produces lots of IgM but little or no IgG

27
Q

What is common variable immunodeficiency

A

Having an IgG or IgA deficiency which is generally a result of inability of B cells to mature into plasma cells

28
Q

Lack of thymus or hypo plastic thymus

A

DiGeorge syndrome is incomplete development of the thymus

29
Q

Secondary immunodeficiency?

A

This is a due of result of external forces

30
Q

Examples of secondary immunodeficiency

A
  • HIV: CD4+ count drops leading to AIDs
  • Malnurition
  • Tumours: some cancer cells release immunosuppressive factors (treated using cytotoxic drugs and radiation)

Immunity and infection (4 decks)

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