What type of reaction is this?

A boy scout returns home after a three-day adventure in the woods with a pruritic, linear, vesicular eruption. His mother brings him to the dermatologist and he is diagnosed with poison ivy dermatitis. What type of reaction is this?

Type I
Type II
Type III
Type IV
Type V

Correct answer
Type IV
correct answer: D

Type IV hypersensitivity reactions are T-cell mediated reactions, which are responsible for the contact dermatitis seen in poison ivy. Type I reactions are anaphylactic (e.g. seasonal allergies). Type II reactions are antibody-antigen mediated (e.g. Goodpasture’s nephritis). Type III reactions are immune complex mediated (e.g. rheumatoid arthritis). Type V reactions are antibody-stimulating (a subtype of Type II) (e.g. Graves disease).