Step 1: Understanding the Question:
We need to identify which hypersensitivity type is driven by cells rather than antibodies, and which shows up after a delay rather than immediately.
Step 2: Key Concept:
Hypersensitivity reactions are grouped into four types, and the deciding factor for this question is whether antibodies or T-cells drive the reaction, and how fast it appears after exposure.
Step 3: Detailed Explanation:
Types I, II, and III are all triggered by antibodies, IgE in Type I, direct cell-bound IgG or IgM in Type II, and immune complexes in Type III, and all of them act within minutes to hours.
Type IV works differently, since it is driven by sensitized T-cells that must first recognize the antigen and recruit other immune cells before a visible reaction develops.
This process takes 24 to 72 hours to appear, giving Type IV its name of delayed-type hypersensitivity, seen in reactions like the tuberculin skin test and contact dermatitis from poison ivy.
Step 4: Final Answer:
Type IV hypersensitivity is the cell-mediated, delayed type.