Which statement best describes the biopsy finding commonly seen in acute renal allograft rejection?

• A. Biopsy shows normal histology.
• B. Biopsy shows a lack of inflammatory cells.
• C. Biopsy shows non-specific changes that do not clarify rejection.
• D. Biopsy in acute rejection often shows interstitial lymphocytic infiltrates with tubulitis.

Answer: (D)

Acute renal allograft rejection is driven by a T-cell–mediated attack on the transplanted kidney. The biopsy most clearly reflects this with an interstitial lymphocytic infiltrate accompanied by tubulitis, where lymphocytes invade the tubular epithelium. This pattern shows active cellular rejection and helps distinguish it from normal tissue, absence of inflammatory cells, or non-specific injury patterns. While other features like endothelial involvement can appear, the combination of interstitial lymphocytes and tubulitis is the classic finding for acute rejection.