A 14-year-old boy develops a pruritic vesicular rash on his face and hands 3 days after hiking in the woods. Which of the following are most likely to be involved in his illness? a. Antibody, complement C5-9
b. Circulating immune complexes; complement C5a, neutrophils
c. Cytotoxic T lymphocytes
d. IgE, mast cells, histamine, cytokines
e. Lymphocytes, cytokines, macrophages

The correct answer is: E) Lymphocytes, cytokines, macrophages.

Explanation:

Given the symptoms and how much time they took to appear, the 14-year-old boy seems to be having delayed-type hypersensitivity (also called Type 4 hypersensitivity), causing a reaction called Contact Dermatitis. Type 4 is the only type of hypersensitivity that does not require the intervening of an antibody to occur as it happens because of hapten-specific T cells that will generate inflammation and the tissue damage that is usually accompanied by it.

Delayed-type hypersensitivity is characterized for happening at least 48 hours after the contact with the antigen, and will involve activated T lymphocytes (specifically CD4+ Th1), which will secrete cytokines (most importantly Interferon Gamma and IL-2) thus attracting macrophages to the tissue to phagocyte the antigen and produce inflammation.