21. Hypersensitivity Reactions - Type IV

Question 1

How long does it take for symptoms of a type IV hypersensitivity reaction to appear after exposure to the antigen?

Answer 1

Delayed response

- peak response 24-72 hours after exposure to Ag

Question 2

In terms of immune mechanism, how is type IV hypersensitivity different from types I, II, and III?

Answer 2

Type IV is a cell-mediated hypersensitivity, involves T cells and macrophage, NOT Antibodies

Question 3

What type of hypersensitivity is induced by exposure to Mycobacterium tuberculosis?

Answer 3

Intracellular pathogen causes Type IV Hypersensitivity reaction

Question 4

What type of hypersensitivity is induced by exposure to poison ivy?

Answer 4

Contact antigen causes Type IV hypersensitivity reaction

Question 5

What does a positive reaction of induration and swelling on a PPD skin test mean clinically?

Answer 5

1. Current infection

2. Past infection (due to memory response of T cells)

Question 6

What type of test is the anergy panel?

Answer 6

A skin test used to determine if a person has functional cell-mediated immunity

Question 7

What does a negative anergy panel mean clinically?

Answer 7

1. A deficiency in cell-mediated immunity (e.g. AIDS, malignancy)
2. Lack of exposure to antigen; response to additional antigens should be tested