Hypersensitivity L4

Question 1

Which type(s) of hypersensitivity are antibody mediated and immediate?

Answer 1

Types 1-3.

Question 2

Which type(s) of hypersensitivity are cell mediated and delayed?

Answer 2

Type 4.

Question 3

Describe Type 1 Hypersensitivity.

Answer 3

On 1st exposure:

• Allergen induces IgE secretion
• IgE binds mast cell FcR

On subsequent exposure:

• Allergen cross-links IgE
• Mast cell degranulates releasing mediators
• Mediators give rise to inflammation

Question 4

Describe IgE production.

Answer 4

• Presentation of antigen to T cells drives a Th2 response. Th2 cells help B cells switch to IgE production.

Question 5

What do IL-4 and IL-13 promote?

Answer 5

IgE production.

Question 6

What does IL-5 increase?

Answer 6

Eosinophil production.

Question 7

List the preformed, immediately released Type 1 hypersensitivity mediators.

Answer 7

• Histamine - Heparin

- TNF-alpha

Question 8

List the newly synthesised, long term release Type 1 hypersensitivity mediators.

Answer 8

• Leukotrienes
• Cytokines
• Chemokines

Question 9

What are the action of mediators in Type 1 hypersensitivity?

Answer 9

• chemotactic
• increase vasodilation and vascular permeability
• bronchial smooth muscle contraction
• increased mucus secretion

Question 10

IL5 from Th2 cells increases production of ______ by bone marrow.

Answer 10

Eosinophils.

Question 11

What attracts eosinophils to the site of inflammation?

Answer 11

Eotaxin (a chemokine).

Question 12

List some type 1 hypersensitivity cause examples.

Answer 12

• Hayfever
• Extrinsic asthma
• Atopic dermatitis
• Food allergy

Question 13

Describe Type 2 Hypersensitivity.

Answer 13

• Antibody (IgG or IgM) produced to antigen on a body cell or tissue
• Cell damage results from interaction of antibody with complement and effector cells

Question 14

Describe the mechanisms of damage in type 2 hypersensitivity.

Answer 14

Complement-mediated lysis
- Antibody activates complement to generate the membrane attack complex

Antibody dependent cell-mediated cytotoxicity (ADCC)
- Extra-cellular killing by cells with Fc receptors (FcR)

Phagocytosis or “frustrated phagocytosis”
- If cell is too large to be phagocytosed release of lysosomal contents can cause tissue damage

Question 15

List some type 2 hypersensitivity cause examples.

Answer 15

• Transfusion reactions
• Haemolytic disease of the newborn
• Autoimmune haemolytic anaemia
• Hyperacute graft rejection

Question 16

Describe Type 3 hypersensitivity.

Answer 16

• Immune complex-mediated
• IgG antibodies complex to antigens
• Complexes deposited in susceptible sites, causing inflammation

Question 17

List some type 3 hypersensitivity cause examples.

Answer 17

• Farmer’s lung
• Erythema nodusum leprosum
• Systemic lupus erythematosus

Question 18

Describe Type 4 hypersensitivity.

Answer 18

• Delayed type hypersensitivity (DTH)
• Not due to antibodies
• T cell-mediated

Question 19

Describe the exposure to antigen in contact dermatisis (Type 4).

Answer 19

First exposure to antigen:

• Ag binds to antigen presenting cells (e.g. skin Langerhans cells)
• APCs move to lymph nodes where T cells are activated

Reexposure to antigen:

• Ag binds again to APCs in skin
• Circulating effector T cells become activated and secrete cytokines leading to inflammation

Question 20

List some type 4 hypersensitivity cause examples.

Answer 20

• Mantoux reaction
• Contact sensitivity
• Granulomata in TB, leprosy

Question 21

Describe Type 5 hypersensitivity.

Answer 21

• Stimulation of cells by antibodies