Final answer:
Poison Ivy, TB Test, and Graft rejections are examples of Type IV hypersensitivity, which is a T cell-mediated immune response leading to inflammation and tissue damage.
Step-by-step explanation:
Poison Ivy, TB Test, and Graft rejections are examples of Type IV hypersensitivity, also known as delayed hypersensitivity. Unlike types I, II, and III hypersensitivities, which are mediated by B cells and antibodies, Type IV hypersensitivity is exclusively a T cell-mediated phenomenon.
In this reaction, upon second exposure to an antigen, memory T cells become activated, releasing inflammatory cytokines that stimulate macrophages and cytotoxic T cells, leading to tissue damage. Common examples include contact dermatitis from substances like poison ivy, and the reaction observed in TB skin tests.