Hypersensitivity

Question 1

Type I

Answer 1

allergic reaction that occurs minutes to hours after contact with allergen.

Question 2

what is type I mediated by, which are produced in repsonse to allergen

Answer 2

IgE

Question 3

What do IgE bind to on surface of mast cells and basophils

Answer 3

FceRI (high affinity receptors)

Question 4

5 effector mechanisms underlying type I

Answer 4

1. histamine release
2. leukotriene release
3. cytokine release (IL-4/5/13) - recruit th2 cells which make more cytokines and promote more IgE production
4. eosinophil activation - recruited by IL-5. secrete toxic granules
5. mucus production

Question 5

3 type I symptoms

Answer 5

sneezing
itching
hives
anaphylaxis

Question 6

Type II

Answer 6

immune-mediated reaction (antibody-dependent cytotoxicity) - kills cells and damages tissues

Question 7

2 effector mechanisms underlying type II

Answer 7

1. complement activation - forms membrane attack complex to lyse the target cell
2. ADCC - abs recruit nk cells and macrophages to kill target cell
3. opsonisation and phagocytosis - antibody-coated target cell recognised and engulfed by phagocytic cells (macrophages and neutrophils)

Question 8

2 diseases caused by type II

Answer 8

HDN
Haemolytic anaemia

Question 9

2 treatments for type II

Answer 9

blood transfusions
immunosuppressive therapy

Question 10

type III

Answer 10

immune-mediated reaction - excess immune complexes in circulation

Question 11

what do immune complexes activate in type iii, leading to tissue damage and inflammation

Answer 11

complement system

Question 12

3 effector mechanisms underlying type III

Answer 12

1. complement activation - activated by ICs, forms membrane attack complex
2. neutrophil activation - release enzymes and ROS - damages tissues
3. platelet activation and aggregation - damages tissues
4. inflammatory cytokine release (IL1 and TNFa) - tissue damage and inflammation

Question 13

2 type iii diseases

Answer 13

systemic lupus
rheumatoid arthiritis

Question 14

what is type 4 hypersensitivity known as

Answer 14

delayed-type hypersensitivity

Question 15

when does type 4 occur

Answer 15

When there’s a cell-mediated immune response against a foreign antigen + tissue damage

Question 16

3 effector mechanisms underlying type 4

Answer 16

1. T cell activation - proliferation and differentiation into cytotoxic T cells and t helper cells
2. Cytotoxic T cell-mediated destruction - destroy cells that display foreign antigen = tissue damage
3. t helper cell-mediated inflammation - t helper cells secrete cytokines (ifn-g, il-17) - activate macrophages and promote inflammation
4. macrophage activation - activated by cytokines from T cells. Phagocytosis of foreign antigens and produce cytokines and ROS

Question 17

some mechanisms both th2 immune responses and allergy share

Answer 17

1. IgE production - th2 cells stimulate b cells
2. eosinophils recruitment - cytokines produced by th2 cells recruit (il5)
3. mucus production - th2 cells produce il13 - stimulates mucous production
4. mast cell activation - activated by il4 produced by th2 cells. mast cells degranulate and release inflammatory mediators.
5. basophils and dendritic cells recruitment - il-9 and il-3 produced by th2

Question 18

what do IgE bind to on surface of mast cells and basophils, leading to their activation and degranulation and cytokines release

Answer 18

FceRI receptors

Question 19

how do mast cells play important role in IS

Answer 19

releasing histamine and cytokines - recruit other immune cells and clear pathogens

Produce growth factors and cytokines for tissue repair

Question 20

what do eosinophils release once activated

Answer 20

release cytotoxic granules, cytokines and chemokine

Question 21

what are main steps in IgE-mediated allergic responses

Answer 21

1. sensitisation - allergen exposure and produce IgE specific to the antigen
2. re-exposure - allergen binds to IgE on mast cells and basophils upon re-exposure
3. cross-linking - allergen binds to IgE and IgE receptors cross-link and activates cells
4. degranulation - granules released by mast cells and eosinophils - allergic reaction symptoms
5. late phase response - several hours after allergen exposure - recruitment of other immune cells which release cytokines and chemokines that can cause tissue damage

Question 22

what is the main trigger of IgE-mediated allergic responses that leads to mast cell activation and degranulation (allergy symptoms)

Answer 22

cross-linking of IgE receptors on the surface of mast cells and basophils by allergens

Question 23

what is atopy the genetic predisposition of

Answer 23

to develop allergic diseases like hay fever, asthma and eczema (IgE production - trigger histamine release)

Question 24

when does HDN occur

Answer 24

when incompatibilty between blood types of a mother and baby . (woman with Rh-neg is carrying baby with Rh-pos)

Question 25

What develop in the mothers bloodstream in HDN which crosses placenta and attacks fetus RBCs

Answer 25

Rh antibodies

Question 26

what is intrinsic allergic alveoli's

Answer 26

allergic lung disease due to inhalation of allergens like dust