5 hypersensitivity and allergies

Question 1

What is immunopathology?

Answer 1

The study of immune system dysfunctions that can cause tissue damage when inappropriately activated.

Question 2

How can the immune system be a “two-edged sword”?

Answer 2

It defends against infection but can also harm the host if improperly activated.

Question 3

What determines the outcome of an immune response?

Answer 3

The type of immune response initiated (e.g., CD4 TH1, TH2, TH17, CD8).

Question 4

What regulates immune responses?

Answer 4

Regulatory T cells (Tregs), which suppress inappropriate activation.

Question 5

What is hypersensitivity?

Answer 5

An inappropriate immune response leading to tissue damage or symptoms.

Question 6

What are the four types of hypersensitivity?

Answer 6

Type I: IgE-mediated (immediate),
Type II: Antibody-mediated (IgG/IgM),
Type III: Immune complex-mediated,
Type IV: T cell-mediated (delayed).

Question 7

What is Type I hypersensitivity?

Answer 7

An immediate allergic reaction caused by allergen-specific IgE binding to mast cells.

Question 8

What immune cell type drives Type I hypersensitivity?

Answer 8

CD4 TH2 cells.

Question 9

What cytokines are involved in Type I hypersensitivity?

Answer 9

IL-4, IL-5, and IL-13.

Question 10

How does an allergen trigger Type I hypersensitivity?

Answer 10

Allergen cross-links IgE on mast cells, causing degranulation.

Question 11

What are pre-formed mediators released in Type I hypersensitivity?

Answer 11

Histamine, heparin, TNF-α.

Question 12

What are newly synthesized mediators in Type I hypersensitivity?

Answer 12

Leukotrienes, cytokines, and chemokines.

Question 13

What are common Type I allergens?

Answer 13

Pollen, house dust mites, food allergens, bee venom.

Question 14

What is anaphylaxis?

Answer 14

A severe systemic allergic reaction with widespread mast cell degranulation.

Question 15

What is the genetic component of Type I hypersensitivity?

Answer 15

Children of allergic parents are more likely to develop allergies; linked to genes like IL-4, IL-33, and FcεRI.

Question 16

What is Type II hypersensitivity?

Answer 16

Antibody (IgG/IgM)-mediated destruction of cells or tissues.

Question 17

What immune mechanisms cause tissue damage in Type II hypersensitivity?

Answer 17

Antibody-dependent cell-mediated cytotoxicity (ADCC), complement activation, frustrated phagocytosis.

Question 18

What are examples of Type II hypersensitivity?

Answer 18

Transfusion reactions, haemolytic disease of the newborn, hyperacute graft rejection.

Question 19

What is haemolytic disease of the newborn (HDN)?

Answer 19

A condition where maternal IgG anti-Rh antibodies attack fetal RBCs.

Question 20

How can HDN be prevented?

Answer 20

By administering anti-RhD antibodies (RhoGAM) to the mother during pregnancy.

Question 21

What is Type III hypersensitivity?

Answer 21

Immune complex (IC)-mediated tissue damage due to failure to clear antigen-antibody complexes.

Question 22

What determines immune complex size and clearance?

Answer 22

The ratio of antigen to antibody.

Question 23

What immune cells are involved in Type III hypersensitivity?

Answer 23

Neutrophils, mast cells, macrophages.

Question 24

What happens when immune complexes deposit in tissues?

Answer 24

Complement activation, neutrophil chemotaxis, inflammation, and tissue damage.

Question 25

Where do immune complexes commonly deposit?

Answer 25

Kidney (glomerulonephritis), skin (rash), joints (arthritis).

Question 26

What is the Arthus reaction?

Answer 26

A local Type III hypersensitivity reaction following subcutaneous antigen exposure

Question 27

What are some diseases caused by Type III hypersensitivity?

Answer 27

Serum sickness, systemic lupus erythematosus, rheumatoid arthritis

Question 28

What is Type IV hypersensitivity?

Answer 28

A delayed T cell-mediated immune response.

Question 29

What cells mediate Type IV hypersensitivity?

Answer 29

CD4 TH1, TH17, and CD8 cytotoxic T cells.

Question 30

What is allergic contact dermatitis?

Answer 30

A Type IV reaction where small chemicals (haptens) modify self-proteins, triggering a T cell response.

Question 31

How do haptens induce a T cell-mediated response?

Answer 31

They bind self-proteins, forming new antigens that activate CD4 T cells.

Question 32

What cytokines are involved in Type IV hypersensitivity?

Answer 32

IFN-γ, TNF-α, IL-3, GM-CSF.

Question 33

What are some examples of Type IV hypersensitivity?

Answer 33

Tuberculin reaction, poison ivy rash, chronic graft rejection.

Question 34

Why is Type IV hypersensitivity delayed?

Answer 34

T cell activation and cytokine-mediated inflammation take time to develop.

Question 35

What is the "hygiene hypothesis"?

Answer 35

Reduced early-life exposure to pathogens leads to an imbalance in immune responses, increasing allergy risk.

Question 36

How prevalent are allergies?

Answer 36

Affect 20-30% of the population.

Question 37

What is the skin prick test?

Answer 37

A diagnostic test for allergies where allergens are introduced into the skin, and a wheal-and-flare reaction is measured.

Question 38

What are the phases of asthma?

Answer 38

Early phase: bronchoconstriction, mucus production. Late phase: cytokine production, inflammation, chronic airway obstruction.

Question 39

What causes food allergies?

Answer 39

Allergen-specific IgE cross-linking on mast cells in the GI tract.

Question 40

What are common symptoms of food allergies?

Answer 40

Oral irritation, nausea, vomiting, anaphylaxis.

Question 41

What is anaphylactic shock?

Answer 41

A life-threatening allergic reaction involving widespread histamine release, leading to cardiovascular collapse.

Question 42

How is anaphylaxis treated?

Answer 42

Epinephrine injection, antihistamines, corticosteroids.

Question 43

What are common treatments for allergies?

Answer 43

Antihistamines, corticosteroids, bronchodilators, epinephrine.

Question 44

What is desensitization therapy?

Answer 44

Gradual exposure to increasing doses of an allergen to reduce IgE-mediated responses.

Question 45

How does desensitization therapy work immunologically?

Answer 45

It shifts the immune response from IgE to IgG4 and induces regulatory T cells.

Question 46

What is Omalizumab (Xolair)?

Answer 46

An anti-IgE monoclonal antibody that blocks IgE binding to mast cells

Question 47

What are some new immunotherapy approaches for allergies?

Answer 47

Blocking cytokines involved in TH2 responses, enhancing Treg function.

Question 48

Why do some allergies persist into adulthood?

Answer 48

Failure to develop tolerance, ongoing IgE production.

Question 49

How does the environment influence allergy development?

Answer 49

Pollution, dietary changes, and reduced microbial exposure can increase allergy risk.

Question 50

What role do eosinophils play in allergic responses?

Answer 50

They release toxic granules that contribute to tissue damage in chronic allergic inflammation.§

Question 51

What are the pre-formed mediators released from mast cells in Type I hypersensitivity?

Answer 51

Histamine, proteases (tryptase, chymase), and heparin.

Question 52

What are newly synthesised mediators produced after mast cell activation?

Answer 52

Prostaglandins (e.g., PGD2), leukotrienes (e.g., LTC4, LTD4, LTE4), and platelet-activating factor (PAF).

Question 53

What effects do histamine have on the body?

Answer 53

Increases vascular permeability, causes vasodilation, and stimulates smooth muscle contraction.

Question 54

What are the roles of prostaglandins and leukotrienes in Type I hypersensitivity?

Answer 54

Prostaglandins (e.g., PGD2) cause vasodilation and bronchoconstriction. Leukotrienes (e.g., LTC4, LTD4, LTE4) enhance smooth muscle contraction and increase vascular permeability.

Question 55

Which immune cells are recruited during the late-phase reaction in Type I hypersensitivity?

Answer 55

Eosinophils, basophils, and TH2 cells.

Question 56

What do eosinophils release in allergic reactions?

Answer 56

Major basic protein (MBP), eosinophil peroxidase (EPO), and leukotrienes.

Question 57

How does omalizumab work as a treatment for IgE-mediated allergies?

Answer 57

It is an anti-IgE monoclonal antibody that prevents IgE from binding to FcεR on mast cells.