hypersensitivity

Question 1

what is the definition of hypersensitivity?

Answer 1

state of altered reactivity in which the body reacts with an exaggerated immune response to a foreign agent

Question 2

what type of reaction is allergy?

Answer 2

hypersensitivity

Question 3

what is an allergen?

Answer 3

an antigen that causes an allergic reaction

Question 4

what are some examples of oral allergies?

Answer 4

• gluten
• peanuts
• eggs
  etc.

Question 5

how many types of hypersensitivity are there (Gell and Coombs’s classification)?

Answer 5

4

Question 6

describe type 1 hypersensitivity

Answer 6

• IgE mediated
• mast cells/basophils
• eg atopy/anaphylaxis

Question 7

describe type 2 hypersensitvity

Answer 7

• cytotoxic responses
• NK cells/complement/T cells (CD8+ cytotoxic)
• eg haemolytic aneamia

Question 8

describe type 3 hypersensitivity

Answer 8

• immune complex responses
• complement/neutrophils
• eg serum sickness

Question 9

describe type 4 hypersensitivity

Answer 9

• cell mediated responses
• T cells/macrophages
• eg sarcoidosis/TB/Crohn’s disease

Question 10

what is the most common type of hyersensitivity?

Answer 10

type 1

Question 11

what is the most rapid type of hypersensitivity?

Answer 11

type 1

Question 12

what is atopy?

Answer 12

genetic predisposition for allergy

Question 13

what is anaphylaxis?

Answer 13

acute, serious allergic response

Question 14

what occurs when allergens bind to IgE antibodies?

Answer 14

• degranulation
• reaction

Question 15

what can allergens be?

Answer 15

proteins or haptens

Question 16

what is a hapten?

Answer 16

• any small molecule that can be recognised by a specific antibody but cannot elicit an immune response
• must be chemically linked to a protein molecule carrier to elicit an antibody/T cell response

Question 17

what occurs on first exposure?

Answer 17

IgE producing B cells activated

Question 18

class switching

Question 19

what is atopy?

Answer 19

the genetic tendency to develop allergic diseases to allergens

Question 20

what are examples of cutaneous atopy?

Answer 20

(localised)
- hay fever
- allergic eczema
- lower respiratory tract

Question 21

what is systemic anaphylaxis?

Answer 21

• anaphylactic shock throughout the body
• arises from mast cell degranulation
• anaphylatoxins can also be produced by a complement cascade (type 2 or 3)

Question 22

what are methods of allergy testing?

Answer 22

• skin prick test/patch test
• blood test
• food challenge (oral)

Question 23

describe anti-allergy drugs

Answer 23

• Avoid allergen
• Drugs
  Anti-histamines – compete with histamine for receptors
  Hydrocortisone – block histamine synthesis
  Cromoglycate – stabilises mast cells stops histamine release
  Epinephrine – best immediate treatment for anaphylactic shock reverses effects of granules (vasoconstriction, relaxes muscles)
• Immunological treatment
  Hypo- or de- sensitisation – repeat injections of allergen
  IgE to IgG production

Question 24

how to anti-histamines act?

Answer 24

compete with histamine for receptors
- histamine receptors have basal activity
- can be inverse agonists or antagonists

Question 25

describe the action of epinephrine

Answer 25

• stimulation of adrenoceptors (anaphylactic shock)
• increases peripheral vascular resistance
• improves blood pressure
• reverses peripheral vasodilation
• causes bronchodilation
• reduces inflammatory mediator release

Question 26

describe in detail type 2 hypersensitivity

Answer 26

• Involves activation of complement by IgG or IgM binding to an antigenic cell (cell surface auto-antigens or haptens/allergens)
• Cell is lysed by;
  Membrane attack complex formation (complement)
  Antibody dependent cell mediated cytotoxicity (natural killer cells or CD8+ T cells)
• Common example – transfusion reactions/autoimmune hemolytic anaemia

Question 27

what are examples of type 2 hypersensitivity?

Answer 27

• transfusion of mismatched blood type
• autoimmune hemolytic anaemia

Question 28

describe in detail type 3 hypersensitivity

Answer 28

• Involves reactions against soluble antigens circulating in serum.
• Antibody-antigen immune complexes are deposited in organs which leads to;
  Complement activation
  Neutrophil recruitment
  Inflammation-mediated damage
• Examples include;
  Arthus reaction
  Serum sickness
  Oralerythema multiforme(EM)

Question 29

what are examples of type 3 hypersensitivity?

Answer 29

• Arthus reaction (localized hypersensitivity reaction)
• Antibody-antigen complexes are localized e.g., blood vessel walls
• Can arise from injected particles (e.g., booster vaccinations) but also can arise from inhaled or ingested allergens (e.g., farmers lung and coeliac disease)

Question 30

what are examples of type 3 hypersensitivity?

Answer 30

• Serum sickness is a systemic form of Arthus reaction
  Antibody-antigen complexes circulate and lodge in many different tissues.
  Similar mechanism occurs as localized form.
• Oralerythema multiforme(EM)
  Characterized by crusty blistering of oral mucosa
  Caused by deposition ofimmune complexes(IgM-bound immune complexes) in the microvasculatureof the oral mucous membrane
  Can be acute inflammatory responses to viral infections e.g., HSV
  Can be caused by hypersensitivity to drugs e.g., Trimethoprim-sulfamethoxazole which is widely administered to treat urinary or lower respiratory tract infections.

Question 31

describe in detail type 4 hypersensitivity

Answer 31

• T cell-mediated hypersensitivity (no antibodies)
• Sometimes called delayed hypersensitivity as takes time to recruit T cells (adaptive immune response)
• Localized T cell reaction at site of antigen exposure (e.g., contact dermatitis)
• Involves both CD4+ T cells (inflammation induced damage via macrophages) and CD8+ T cells (direct damage of cells – cytotoxicity)

Question 32

what are examples of type 4 hypersensitivity?

Answer 32

• Contact dermatitis
• Tissue graft rejection
• Response to intracellular pathogens (e.g., TB) – characterized by the formation of granulomas in lung tissue.
• Oral diseases – Orofacial granulomatous (OFG)?

Question 33

what makes type 4 hypersensitivity different?

Answer 33

no antibodies