A patient develops a red, itchy rash two days after wearing a bracelet containing nickel. The reaction is caused by a delayed-type hypersensitivity response. Which immune cell type is primarily responsible for initiating this reaction?

The reaction in type IV hypersensitivity typically peaks:

During a primary adaptive immune response, naive T helper (CD4+) cells recognize antigen presented by dendritic cells and begin proliferating. After roughly what period do these activated cells usually give rise to detectable memory CD4+ T cells?

Haptens are unique because:

During a tuberculosis screening program, a patient shows significant induration 48 hours after receiving a tuberculin skin test. The clinician explains that this result alone cannot confirm active tuberculosis. Why is additional testing necessary?