Week 4- Hypersensitivity

Question 1

What are antibody classes know as? How do they differ?

Answer 1

Isotypes, they have different binding capacities and engage with the immune system in different ways

Question 2

How are T cells activated?

Answer 2

By encountering a specific antigen

Question 3

What do effector CD4+ T cells do?

Answer 3

Activate B cells, macrophages

Question 4

What do effector CD8+ T cells do?

Answer 4

Kill infected target cells and activate B cells

Question 5

What is type I hypersensitivity?

Answer 5

Allergic reaction where antibodies are produced against common multivalents (antigens that have multiple sites for antibody attachment)

Question 6

What antibodies mediate type I hypersensitivity?

Answer 6

IgE

Question 7

Describe the pathway of a type I hypersensitivity reaction

Answer 7

1. B cell helper follicular CD4 T cells and type 2 helper CD4 T cells produce type 2 cytokines IL3 and IL4
2. These encourage B cells to produce antigen specific IgE
3. IgE binds to mast cells and basophils via Fc epsilon receptor
4. Cross linking and degranulation of basophils/mast cells results in the release of histamine
5. Results in Th2 differentiation

Question 8

What are the 3 phases of type I hypersensitivity reactions and what are their time frames?

Answer 8

1. Early phase- mast cells produce small molecules (few mins)
2. Later phase- Recruitment of neutrophils (few hrs)
3. Third phase- recruitment of eosinophils and Th2 cells (3/4 days)

Question 9

What happens in type II hypersensitivity reactions?

Answer 9

Destruction of cells by IgG or IgM antibodies binding to antigens on the cell surface

Question 10

What are some examples of type II hypersensitivity reactions?

Answer 10

Haemolytic disease
Graves’ disease
Mismatched blood transfusion

Question 11

What are the 3 methods by which antibodies can cause disease? Describe them

Answer 11

1. Anti receptor activity
2. Antibody dependent cell mediated cytotoxicity- when antibody antigen complexes cause lysis
3. Activation of a complement cascade- antibody is recognized by complement components which leads to the formation of a membrane attack complex (MAC) causing cell death due to lack of integrity

Question 12

What is type III hypersensitivity?

Answer 12

When antibody antigen complexes aren’t removed and deposited in blood vessels, causing inflammation and tissue damage

Question 13

What is type III hypersensitivity in the blood vessels called?

Answer 13

Vascularitis

Question 14

What is type III hypersensitivity in the kidneys called?

Answer 14

Glomerulonephritis

Question 15

What is type III hypersensitivity in the joints called?

Answer 15

Arthritis

Question 16

What occurs in systemic lupus erythematosus and where in the body?

Answer 16

Anywhere in the body, type III hypersensitivity reactions occur. Increases apoptosis leading to neutrophil dysregulation

Question 17

What happens in serum sickness? What type of hypersensitivity is it associated with?

Answer 17

Type III, when people are bitten by snakes they form antibodies against the venom, so when they are bitten the second time there is immediate and rapid inflammation

Question 18

What is type IV hypersensitivity?

Answer 18

It is T cell mediated, where memory T cells are produced against an antigen over several weeks and 2nd exposure drives response (takes 2/3 days)

Question 19

What is the most common example of type IV hypersensitivity?

Answer 19

Contact dermatitis (an antigen in poison ivy)