Final answer:
A. Hypersensitivity reaction. Delayed hypersensitivity is a type IV hypersensitivity reaction involving lymphocytes and mononuclear phagocytes. It reaches its peak intensity 24 to 48 hours after initiation and is a cell-mediated immune response.
Step-by-step explanation:
Delayed hypersensitivity, also known as type IV hypersensitivity, is the tissue reaction involving lymphocytes and mononuclear phagocytes in response to a soluble protein antigen. This reaction reaches its peak intensity 24 to 48 hours after initiation. The immune response in delayed hypersensitivity is cell-mediated and involves sensitized T cells secreting cytokines that recruit macrophages and phagocytes to the site of antigen exposure.