Step 1: Understanding the Concept:
The question asks which hypersensitivity type is called cell-mediated and delayed.
Step 2: Key Concept or Approach:
Types I, II, and III hypersensitivity are all driven mainly by antibodies and act fast, within minutes to a couple of days. Only one type is driven by T cells instead of antibodies and takes longer to appear.
Step 3: Detailed Explanation:
Type I is IgE-driven and appears within minutes, as in allergic reactions.
Type II is antibody-driven cell destruction, as in hemolytic anemia.
Type III involves antigen-antibody complexes depositing in tissue, as in serum sickness.
Type IV does not use antibodies at all, instead sensitized T lymphocytes and macrophages recognize the antigen and mount a response that takes one to three days to build, giving it both the "cell-mediated" and "delayed" labels, as seen in the tuberculin test and contact dermatitis.
Step 4: Final Answer:
Type IV hypersensitivity is the cell-mediated, delayed type.