Hypersensitivity Disorder

Question 1

Describe type I hypersensitivity reaction.

Answer 1

IgE mediated from mast cells. contribute to anaphylactic reaction

Question 2

Describe type II hypersensitivity.

Answer 2

Mediated by Ab that bind tissue Ag and activate complement to degrade specific tissue. Causing tissue injury/disease.

Question 3

Describe Type III hypersensitivity.

Answer 3

Form from Ab-Ag complex that form in the blood, and settle in the vascular lining. Causing vasculitis

Question 4

Describe a Type IV hypersensitivity reaction.

Answer 4

T cell mediated from inflammation by cytokines.

Ultimately from Th17, Th1 cells or killing CTL

Question 5

What is the mechanism of a type I allergic reaction?

Answer 5

1. Mast cells cross-link to IgE bound on Ag.
2. Mast cells release pre-formed cytokines, vasoactive amines
3. Also attract neutrophils/eosinophils

Question 6

Where do mast cells bind to their high affinity IgE molecules?

Answer 6

Fc(epsilon)RI

Question 7

What occurs in the immediate phase reaction of type I reactions?

Answer 7

Vascular and smooth muscles react within minutes.

1. Generally vasodilation, bronchoconstriction, edema, congestion

Question 8

What occurs in the laste phase of type I allergic reactions?

Answer 8

Inflammation caused by eosinophils, neutrophils and T cells

Question 9

What is the role of leukotrienes?

Answer 9

Prolonged smooth muscle contraction (bronchi) increase vascular permeability

Question 10

What is the role of proteases in type I allergic reaction?

Answer 10

Tissue damage

Question 11

What is the role of vasoactive amines in a type I allergic reaction?

Answer 11

Cause vasodilation, smooth muscle contraction (bronchi)

Question 12

What is the role of cytokine secretion during type I allergic reaction?

Answer 12

Cause inflammation and leukocyte recruitment for late phase response

Question 13

What are the effector mechanisms of type II allergic reaction?

Answer 13

1. Abs opsonize which activate complement and phagocytosis via CR1/FcR affinity for C3b
2. C3a/C5a recruit leukocytes
3. Ab can stimulate/inhibit a glands receptor

Question 14

What disease can be caused by Ab binding during a type II allergic reaction?

Answer 14

Ab bind with TSHreceptor, causing hyperthyroidism (Grave’s disease)

Question 15

What binding can be inhibited in a type II allergic reaction by the antibody?

Answer 15

Inhibition of Ach binding to receptor causing myasthenia gravis

Question 16

How does a type III reaction occur?

Answer 16

Endothelial Fc receptors bind the antitoxin-toxoid complex. This leads to accumulation/agglutination, which activates classical complement cascade and doing so causes vasculitis.

Question 17

What can the Arthur’s reaction be compared to?

Answer 17

Type III allergic reaction. Exactly similar to the toxin-toxoid mechanism

Question 18

What human diseases are caused by type III allergic reaction?

Answer 18

1. SLE
2. Polyarteritis nodosa
3. Post-streptococcal glomerulonephritis
4. Serum sickness
5. Arthus reaction

Question 19

What are triggers for Type IV reaction?

Answer 19

Autoimmune, with persisten environmental or microbial Ags

Question 20

What causes tissue injury in Type IV that sets it apart from Type I, II, III?

Answer 20

Uses cell mediated. No Ig families.

- activates Th1, Th17, CTL cells to induce tissue injury

Question 21

What are the common forms of type IV reactions?

Answer 21

1. MS
2. Rheumatoid arthritis
3. DM type 1
4. Crohn’s disease
5. Contact sensitivity (similar to type I, longer incubation time)
6. Chronic infections (TB)

Question 22

What are contained in granulomas?

Answer 22

1. Activated macrophages
2. PMN
3. T cells

Question 23

What is a hypersensitivity response?

Answer 23

Immune response causing tissue injury