A bone marrow transplant recipient develops graft-versus-host disease (GVHD) 30 days post-transplant. This reaction is best classified as which type of immunological response?
- A Type II hypersensitivity (antibody-mediated cytotoxicity)
- B Type III hypersensitivity (immune complex-mediated)
- C Type IV hypersensitivity (cell-mediated) by donor T cells ✓
- D Type I hypersensitivity (IgE-mediated)
Correct answer: C. Type IV hypersensitivity (cell-mediated) by donor T cells
Explanation
GVHD is mediated by donor T lymphocytes recognising host allogeneic MHC antigens as foreign and mounting a cell-mediated (Type IV) cytotoxic response against host tissues. The skin, gut, and liver are principal target organs. This is distinct from host-versus-graft rejection, which involves the recipient's immune system. Type I (IgE), Type II (cytotoxic antibody), and Type III (immune complex) mechanisms do not primarily account for GVHD.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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