3.1.3 Cutaneous Allergic Reaction

Question 1

Tuberculin PPD skin test is an example of what type of hypersensitivity?

Answer 1

Type IV

Question 2

CD4 T cells are activated when they recognize antigens presented by?

Answer 2

MHC class II

Question 3

Pathology report referred to a sample as having a mononuclear cellular infiltrate and a diagnosis of allergic contact dermatitis was later established. What is the likely cells that were in the infiltrate?

Answer 3

T cells and macrophages constitute most of a mononuclear infiltrate in DTH lesions

Question 4

What test would be performed to assess the possibility of allergic contact dermatitis?

Answer 4

Patch test - applying patches impregnates with various allergens to the patient

Question 5

How long do you leave the patches on during a patch test?

Answer 5

72hrs

Question 6

Linear rash can be associated with?

Answer 6

A contact dermatitis due to the brushing motion against the allergen

Question 7

What is the basic overview of allergic contact dermatitis?

Answer 7

Metal or other hapten exposure leads to sensitization. The antigen is presented on MHC class I and II. CD4 and CD8 expansion. Upon re-exposure to hapten there is T cell recruitment and macrophage recruitment and activation. This leads to inflammatory mediator production.

Question 8

What is the basic process of sensitization?

Answer 8

First exposure leads to binding to skin proteins and formation of neoantigen. The Ag is then presented on MHC II and creation of CD4 and CD8 memory cells.

Question 9

After sensitization and upon second exposure what happens?

Answer 9

Memory T cells and activated macrophages lead to the production of chemokines and IFN-gamma. This can have two outcomes: CD4 T cells down reg inflammation via T reg cells or the production of inflammatory mediators-PGs, LTs, and proteases. This lead to complement anaphylatoxins and then mast cell mediators