Mild acute rejection is characterized by a generally mild and localized inflammatory infiltrate, which tends to be concentrated around small venules in the lamina propria. The mucosa is intact, but the crypt epithelium displays evidence of injury: mucin depletion, cytoplasmic basophilia, decreased cell height, nuclear enlargement and hyperchromasia, and inflammatory infiltration. The crypt epithelial apoptosis is increased, usually with more than 6 apoptotic bodies/10 crypts. If sampled by the biopsy specimen, preexisting lymphoid aggregates (Peyer's patches) demonstrate an intense accumulation of activated lymphocytes. The villi are variably shortened and the architecture may be slightly distorted due to expansion of lamina propria by inflammatory infiltration