In HLA typing for renal transplantation, a patient receives a kidney that is matched for HLA-A, B but mismatched for one HLA-DR locus. Within 6 months, the graft is lost to an irreversible cellular rejection episode. The T cell population primarily responsible for recognizing the mismatched HLA-DR on donor antigen-presenting cells by DIRECT allorecognition is:
- A CD8+ cytotoxic T cells
- B CD4+ helper T cells ✓
- C NK cells via KIR receptors
- D Regulatory T cells (Tregs)
Explanation
In direct allorecognition, recipient T cells recognize intact donor MHC-peptide complexes on donor APCs. CD4+ T cells recognize donor MHC class II (HLA-DR) molecules directly, which is the primary pathway in acute cellular rejection. This CD4+ T cell activation drives differentiation of cytotoxic CD8+ T cells and promotes antibody-mediated rejection through B cell help. HLA-DR mismatch is particularly immunogenic and is the strongest predictor of rejection among HLA mismatches. NK cells use KIR receptors for missing self recognition, not direct allorecognition.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.