A patient receives a skin graft from a sibling who is HLA-haploidentical. The graft is rejected at 12 days. Which immunological mechanism is primarily responsible?
- A Antibody-dependent cellular cytotoxicity by NK cells
- B Complement activation via classical pathway
- C Direct allorecognition by host CD8+ cytotoxic T cells ✓
- D Type I hypersensitivity triggered by graft proteins
Correct answer: C. Direct allorecognition by host CD8+ cytotoxic T cells
Explanation
Acute cellular rejection occurring at 7–21 days is primarily mediated by direct allorecognition — host T cells recognize intact donor MHC-peptide complexes on graft cells as foreign. CD8+ cytotoxic T lymphocytes destroy graft cells expressing non-self MHC class I. Direct recognition is quantitatively more potent than indirect recognition in the early post-transplant period. ADCC and complement are more relevant in hyperacute antibody-mediated rejection. Type I hypersensitivity involves IgE and mast cells and is not a transplant rejection mechanism.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.