Disorders of immune system

Question 1

Give 5 examples of things that could cause a type 1 hypersensitivity reaction

Answer 1

• Pollen
• Animal hair
• house dust mite
• moulds
• insect bites
• food - peanuts
• latex
• medicine - penicillin

Question 2

What is the process of a pollen allergy?

Answer 2

• First exposure - B cells recognise the Ag, internalise it and present to Th2 cells, which secrete IL-4, starting class-switching - B cells make IgE
• IgE produced from previous allergen exposure diffuses through body
• IgE binds to mast cells by its Fc region into mast cell Fc receptors

Second exposure to pollen

• Pollen enters and binds to the Ig, if pollen cross-links the IgE on the mast cell, it will release Histamine
• Mast cells generate other cytokines, encouraging Th cells to also produce cytokines - prolongs allergic reaction

Question 3

What causes a type II reaction?

Answer 3

Ag and Ab interaction of IgM

Question 4

Gives some examples of type II reactions

Answer 4

• Myasthenia gravis
• Rhesus isoimmunisation
• HDN
• Graves

Question 5

What happens in myasthenia gravis?

Answer 5

• In healthy individuals, nerve impulses trigger release of Ach from nerve endings, binds to AchR on muscle cells triggering contraction
• In MG, autoantibodies to AchR are produced. These block the AchR at the postsynaptic NMJ, diminishing muscle contraction
• Causes muscle atrophy

Question 6

What happens in Rhesus isoimmunisation?

Answer 6

• RhD Ag is carried on RBCs
• If RhD-ve mother has baby with RhD+ve father, mother will become sensitised to RhD and make Abs
• In the second pregnancy, if the foetus is Rh+ve, small amounts of RBCs crossing placenta stimulate memory cells
• This causes production of more anti-RhD Abs, which cross the placenta and cause HDN

Question 7

What happens in Grave’s disease?

Answer 7

• Autoantibodies are made that act on TSHR on thyroid

- Causes lots of TH to be made

Question 8

What happens in myasthenia gravis?

Answer 8

• In healthy individuals, nerve impulses trigger release of Ach from nerve endings, binds to AchR on muscle cells triggering contraction
• In MG, autoantibodies to AchR are produced. These block the AchR at the postsynaptic NMJ, diminishing muscle contraction
• Causes muscle atrophy

Question 9

What causes a type II reaction?

Answer 9

Ag and Ab interaction of IgM

Question 10

What is a type IV reaction?

Answer 10

• Delayed hypersensitivity
• T-cell mediated but DCs, macrophages and cytokines contribute to process
• e.g. Mantoux test, Type 1, coeliac, IBD, Crohns, psoriasis

Question 11

What happens in myasthenia gravis?

Answer 11

• In healthy individuals, nerve impulses trigger release of Ach from nerve endings, binds to AchR on muscle cells triggering contraction
• In MG, autoantibodies to AchR are produced. These block the AchR at the postsynaptic NMJ, diminishing muscle contraction
• Causes muscle atrophy

Question 12

Define a type III reaction

Answer 12

• Type III target is soluble circulating Ag
• Ag can be own tissue or foreign material
• e.g. SLE

Question 13

What happens in SLE?

Answer 13

• Aetiology unknown, but familial pattern
• Make autoantibody directed against self molecules including DNA and nuclear ribonucleoproteins
• Forms immune complexes - get trapped in kidney and cause glomerulonephritis
• The Abs can fix complement - tissue injury
• Abnormal activation of B cells - more sensitive to stimulatory cytokines
• Reduced Th1 response
• probs with phagocytes mean that they cant clear immune complexes

Question 14

What is a type IV reaction?

Answer 14

• Delayed hypersensitivity
• T-cell mediated but DCs, macrophages and cytokines contribute to process
• e.g. Mantoux test, Type 1, coeliac, IBD, Crohns, psoriasis

Question 15

What is the mantoux test?

Answer 15

• TB vaccine test
• Inject pt with extract of mycobacterial Ag in skin
• Macrophages present ag to activate Th cells - release cytokines to activate macrophages, which release cytokines
• Red swelling of skin

Question 16

What components can lead to immundeficiency?

Answer 16

• complement - C1q inhibitor deficiency -> hereditary angioedema (continuous complement activation)
• C3 deficiency -> infection
• Phagocytes - Chediak-Higashi (failure of phagolysosome formation and lysosome degranulation)
• B cell deficiencies - SCID (lack of development of stem cells into B or T cells)
• Hyper IgM (increased IgM but little or no IgG)
• Common variable immunodeficiency (IgG/A deficiency - B cells unable to mature into plasma cells)
• T cell deficiencies
• Lack of thymus -> DiGeorge

Question 17

What happens in coeliac?

Answer 17

• Small intestine disease
• HLA type imortant
• Patients have IgA anti-gliadin, antiendomysium and antireticulin Abs
• T cells present in intestine
• Causes villous atrophy
• Leads to malbsorption

Question 18

What causes psoriasis?

Answer 18

• Chronic skin disease - red plaque with silvery scales
• Genetic and environmental factors
• lots of CD4+ cells in skin
• Immunosuppressive treatment is effective

Question 19

What factors contribute to development of autoimmune disease?

Answer 19

• Age and gender (autoantibodies more common in elderly, SLE and Grave more common in women)
• Drugs
• Immunodeficiency

Question 20

What components can lead to immundeficiency?

Answer 20

• complement - C1q inhibitor deficiency -> hereditary angioedema (continuous complement activation)
• C3 deficiency -> infection
• Phagocytes - Chediak-Higashi (failure of phagolysosome formation and lysosome degranulation)
• B cell deficiencies - SCID (lack of developmnt of stem cells into B or T cells)

Question 21

What can cause secondary immunodeficiency?

Answer 21

• HIV infection - AIDS
• Malnutrition
• Tumours - cancerous cells can release immunosuppressive factors
• Cytotoxic drugs/ radiation