A-IV Allergies

Question 1

Hypersensitivity reactions

Answer 1

Exaggerated immune response that causes deleterious effects and damage

Question 2

Type I hypersensitivity

Answer 2

Mediated by IgE and the activation of mast cells, resulting in an immediate reaction.

Question 3

Type IV hypersensitivity

Answer 3

T-cell mediated, also known as delayed type hypersensitivity (DTH), involving activated T-cells and macrophages.

Question 4

Allergy

Answer 4

A disease caused by an excessive response to a foreign antigen, involving Type I and IV hypersensitivity.

Question 5

Autoimmune disease

Answer 5

A disease caused by a failure of self-tolerance, involving Type II and III hypersensitivity.

Question 6

IgE

Answer 6

An antibody produced in response to allergens. Four constant domains (Fc), no hinge, very potent

Question 7

FcεRI

Answer 7

The Fc receptor for IgE, found on mast cells in tissues and basophils in blood

Question 8

Allergens

Answer 8

Examples include proteins in pollen, house dust mites, animal dander, and foods. They are often characterized by low molecular weight and high solubility.

Question 9

Mast cells

Answer 9

Immune cells that carry allergen-specific IgE on their surface via FcεRI. Upon allergen binding, they release granules containing histamine. They are located near blood vessels, nerves, and beneath the epithelium.

Question 10

Histamine

Answer 10

A mediator released from mast cell granules that causes smooth muscle contractions and increased vascular permeability.

Question 11

Anaphylaxis

Answer 11

A severe allergic reaction characterized by restriction of the airway due to mast cell-derived mediators, leading to cardiovascular collapse and potentially death.

Question 12

Asthma (in allergy)

Answer 12

An allergic condition involving muscle tightening, lining swelling, and excess mucus in the airways.

Question 13

Delayed type hypersensitivity (DTH)

Answer 13

An allergic reaction mediated by activated T-cells, leading to a feedback loop with macrophages. Examples of allergens include insect venom and poison ivy.

Question 14

Allergen desensitization / Immunotherapy

Answer 14

A treatment for allergic disease involving injecting patients with escalating doses of antigen to change the immune response from IgE to IgG and induce Tregs.

Question 15

Qhat characterizes a Type I hypersensitivity reaction?

Answer 15

Type I hypersensitivity is induced by antibodies, specifically IgE, which leads to the activation of mast cells and an immediate reaction with symptoms appearing within minutes.

Question 16

What is the main characteristic of a Type IV hypersensitivity reaction?

Answer 16

Type IV hypersensitivity is T-cell mediated and is also known as delayed type hypersensitivity (DTH), involving the activation of T-cells and a feedback loop with macrophages.

Question 17

What is the role of IgE in allergic reactions?

Answer 17

IgE is produced in response to allergens. It binds to the Fc receptor for IgE (FcεRI) which is found on mast cells in tissues and basophils in blood. When IgE on mast cells connects to an allergen, it triggers the release of granules containing histamine.

Question 18

Can you provide some examples of allergens?

Answer 18

Examples of allergens include proteins in pollen, house dust mites, animal dander, and foods.

Question 19

What are some key characteristics of allergens?

Answer 19

Allergens are often characterized by low molecular weight and high solubility in body fluids. They can also be enzymes. Importantly, they are generally not polysaccharides unless connected to proteins, in which case they can have a hapten-carrier effect. They also do not stimulate innate immune responses directly but may drive towards the Th2 pathway and IL-4 production, stimulating mast cells. They do not have PAMPs.

Question 20

What are the primary actions of histamine released during an allergic reaction?

Answer 20

Histamine release leads to smooth muscle contractions and increased vascular permeability.

Question 21

Describe the process of mast cell activation in an allergic reaction.

Answer 21

Mast cells carry allergen-specific IgE on their surface, bound to FcεRI. When this IgE connects to an allergen, the mast cell is activated, and granules containing histamine are released.

Question 22

What are some of the mediators stored in mast cell granules?

Answer 22

Mast cell granules contain histamine, heparin and/or chondroitin sulfate, and proteases.

Question 23

What are some of the cytokines produced and released by mast cells after activation?

Answer 23

Mast cells synthesize and release cytokines such as IL-4, IL-13, and IL-33, which promote Th2 differentiation and IgE production; IL-5, which promotes eosinophil production and activation; and TNF-alpha, which contributes to inflammation.

Question 24

What are the roles of leukotrienes and prostaglandins in allergic reactions?

Answer 24

Leukotrienes (like LTC4) cause bronchoconstriction, while prostaglandins (like PGD2) act as vasodilators and bronchoconstrictors.

Question 25

How do connective tissue mast cells and mucosal mast cells differ in terms of location and contents?

Answer 25

Connective tissue mast cells are found in vascularized connective tissue and skin and their granules contain tryptase, chymase, cathepsin G-like protease, and carboxypeptidase. Mucosal mast cells are located in the intestinal mucosa and lung and their granules mainly contain tryptase.

Question 26

What triggers basophil activation in allergic reactions?

Answer 26

Basophil activation is triggered by antigen binding to IgE bound to FcεRI on the cell surface.

Question 27

What is the role of Th2 cells in allergy?

Answer 27

Th2 cells produce IL-4, which activates B-cells to secrete IgE; IL-5, which promotes the activation and recruitment of eosinophils; and IL-13, which activates the epithelium.

Question 28

What is celiac disease?

Answer 28

Celiac disease is described as an immune response to α-gliadin, found in wheat, oat, etc. It involves CD4+ cells, plasma cells, and macrophages infiltrating the upper small intestine, leading to the destruction of villi. It is also noted that both autoimmune and allergic reactions are involved, with the presence of IgA autoantibodies to transglutaminase being a diagnostic marker.

Question 29

How are mast cells produced?

Answer 29

From progenitor cells in bone marrow, then they migrate directly tissue as immature cell and differentiate in the tissue

Question 30

How is the Th2 activated?

Answer 30

Mast cells release IL-4, IL-13, TNF-alpha, which causes Th2 differentiation (and also inflammation)

Question 31

How does the compliment system trigger mast cells in connective tissue?

Answer 31

C5aR1 (receptor) that can be activated by C5a. Also has C3aR

Question 32

Which mast cells have TLRs?

Answer 32

Mucosal mast cells

Question 33

Describe different pathways of mast cell activation

Answer 33

DC present allergen for Naive T-cell -> differentiation to Th2 cell -> IL-4 cause B cells to isotype switch to IgE -> Binds to FcεRI -> binding of antigen to FcεRI cause granule release -> IL-9 activates mast cells to release granule

Question 34

What is a non-atopic reaction?

Answer 34

When mast cells are activated independently of IgE, such as with chemokines, complement.

Question 35

What are some causes of allergy?

Answer 35

Genetic susceptibility (atopic), too clean environment (non-atopic)

Question 36

True or False: Type I hypersensitivity reactions are mediated by IgG antibodies.

Answer 36

False; they are mediated by IgE antibodies

Question 37

True or False: Allergies are diseases caused by an excessive immune response to foreign antigens and involve Type I and Type IV hypersensitivity.

Answer 37

True

Question 38

True or False: Autoimmune diseases are caused by an excessive response to foreign antigens.

Answer 38

False; its a response to self antigens

Question 39

True or False: IgE is an antibody produced by the body in response to allergens

Answer 39

True

Question 40

True or False: The Fc receptor for IgE (FcεRI) is found on the surface of T-cells.

Answer 40

False; it is found on the surface of mast cells and basophils, as well as eosinophils

Question 41

True or False: Allergens are typically large polysaccharide molecules with low solubility in body fluids.

Answer 41

False

Question 42

True or False: Mast cells have FcεRI receptors on their surface that bind IgE, and when this IgE binds to an allergen, the mast cell releases granules containing histamine.

Answer 42

True

Question 43

True or False: Anaphylaxis is a severe allergic reaction that can involve the restriction of the airway.

Answer 43

True

Question 44

True or False: Individuals with atopic conditions typically have low IgE responses to allergens compared to normal individuals.

Answer 44

False

Question 45

True or False: Delayed type hypersensitivity (DTH), or Type IV hypersensitivity, is primarily mediated by antibodies.

Answer 45

False; they are mediated by T-cells and macrophages

Question 45

True or False: Allergen desensitization or immunotherapy aims to change the immune response to an allergen from a IgG response to an IgE response.

Answer 45

False; its the other way around

Question 46

True or False: Histamine, released from mast cells, causes smooth muscle contractions and increased vascular permeability

Answer 46

True

Question 47

True or False: Mucosal mast cells are predominantly found in vascularized connective tissue and skin.

Answer 47

False; it is mainly found in lungs and intestinal mucosa

Question 48

True or False: Basophils do not express FcεRI receptors on their surface.

Answer 48

False

Question 49

True or False: The cytokine IL-4 promotes the differentiation of Th1 cells.

Answer 49

False; they promote the differentiation of Th2 cells

Question 50

Atopic allergic reaction

Answer 50

Driven by IgE, activates mast cells, basophils and eosinophils with FcεR

Question 51

Non-atopic allergic reaction

Answer 51

Mast cells activated independently of IgE, by IgG, cytokines or complement