Type IV Hypersensitivity

Question 1

Type IV hypersensitivity is also known as ___________ hypersensitivity.

Answer 1

Delayed

Question 2

What does a Type IV hypersensitivity respond to?

Answer 2

Injected antigens or uncleared antigens

Question 3

What are the steps of a Type IV hypersensitivity response (4)?

Answer 3

1. Antigen injected into dermis, picked up by langerhan cells, transported to lymph node
2. Langherhan cells, in LN, interacte with memory Th1 cells
3. Memory cells migrate to dermis and secrete cytokines; IFNgamma is most important
4. These cytokines and chemokines draw in macrophages and create inflammatory rxns

Question 4

Type IV hypersensitivity can be transferred by transferring what?

Answer 4

Cells

Question 5

What is a TB test and how do you determine a positive?

Answer 5

1. Skin fold thickness is measured between avian and bovine tuberculosis
2. If the response to M bovis is significantly greater than M avium, the animal is considered to be a reactor, meaning it is or has been infected with M. bovis

Question 6

How can false negatives and false positive be seen with the TB test?

Answer 6

1. False negatives- if the infection is in the early stages or if alterations in immune function are seen (recent post-partum, advanced disease, or very old animals)
2. False positives- if the animal is infected with other types of mycobacteria

Question 7

What are other protocols to increase the sensitivity of the test (3)?

Answer 7

1. Short thermal
2. Stormont
3. Stimulate lymphocytes in vitro with mycobacterial antigen

Question 8

What are the pathological consequences of Type IV hypersensitivity?

Answer 8

a. Tubercle formation
b. Allergic contact dermatitis
c. Mucocutaneous disorders- epidermal loss disorders

Question 9

9. Tubercle formation can be caused by what three things?

Answer 9

1. Granuloma/ granulomatous inflammation
2. Persistant infectious agents- tuberculosis, brucellosis, certain fungal infections
3. Foreign material

Question 10

Toxic epidermal necrolysis and variants are associated with the administration of what?

Answer 10

Drug administration such as trimethoprim sulfa, beta-lactam antibiotics (penicillin, cephalexin)

Question 11

What are the three typical disorders associated with epidermal necrolysis?

Answer 11

1. Erythema multiforme- patchy skin loss

2. Stevens Johnson- 30% skin loss

Question 12

What are the range of clinical signs associated with toxic epidermal necrolysis and variants?

Answer 12

a. Blistering, skin sloughing
b. Fluid loss and electrolyte imbalances
c. Secondary infections