Which type of allograft rejection is characterized by vascular and parenchymal injury with lymphocyte infiltrates?

• A. Hyperacute rejection
• B. Acute cellular rejection
• C. Acute humoral rejection
• D. Chronic rejection

Answer: (B)

Vessel and parenchymal injury accompanied by lymphocyte infiltrates is the pattern seen in acute cellular rejection. Here, recipient T cells recognize donor MHC antigens on graft cells, become activated, and attack both the graft’s blood vessels and its parenchymal tissue. The resulting damage is driven by a dense infiltrate of lymphocytes, often with endothelial injury in the graft vasculature and accompanying parenchymal cell damage. This distinguishes it from hyperacute rejection, which is antibody-mediated and occurs very early with rapid thrombosis and neutrophilic injury; from acute humoral rejection, which involves antibodies and complement (often with C4d deposition) and a different inflammatory profile; and from chronic rejection, which develops over a longer period with fibrosis and vascular smooth muscle proliferation.